I think that a place to share computer hardware experiences/issues migth be useful at a number crunching platform like this.
Please, feel free to share here experiences you consider interesting/useful for other colleagues.

Let's classify crunchers generally into two large groups.
One day something fails at hardware level in one of your rigs, and:
-1) You take it to computer shop/workshop to get it serviced by specialized personnel
-2) You open your rig and try to find and solve the problem by yourself

I classify myself into group number 2 (unless failing rig is under warranty)

I'll start by sharing a simple tip.
This will "sound" familiar to many of you:
For any reason, you stop for a while your usually 24/7 crunching rig.
You return, switch it on again, and a loud (awful) noise starts to sound.
You've got it: probably one (or more) fan(s) is (are) in the need to be replaced.

Sometimes it is clear which fan is failing, other times you have to stop fans one by one until noise stops (You have found it!), and other times fan heats and sound stops by itself after some minutes...
In that situation, I'm not happy until I catch failing fan and replace it.
A noisy fan has a loss in cooling performance, and some valuable component(s) may overheat.
And also it breaks something more invaluable: Quietness at Home:-)

Fans could be classified into three large groups, depending in how the rotor shaft is mounted:
-1) Sleeve bearing
-2) Ball bearing
-3) Magnetic/Flux bearing
They are classified in ascending lifespan... and cost.
I recommend not to try saving money in this component.
In the event to choose between type 1 (sleeve bearing) or 2 (ball bearing), I'd recommend type 2. Or better type 3 if available.
While type 1 fans are cheaper, type 2 and 3 usually feature greater reliability and longer lasting.

Sometimes, in fan references there is some clue indicating their type. If not directly indicated, reference may contain some "S" for sleeve, or "B" for ball bearing. It can be seen in this photo.


Replacing a fan is usually a simple task, requiring only a screwdriver, cable ties, and cutting pliers. It does worth the job.
For this operation, always shut down computer and disconnect it from power.
Once disconnected, press briefly computer's "Power" button to release any remaining voltages at PSU.
Also, touch some metallic part from chassis before touching any inside component. This will prevent damages due to electrostatic discharges.
Then, take note/photo of air flux direction in damaged fan, unscrew it and disconnect cable from its socket, replace by new fan taking care to keep original air flux direction, and connect it to fan socket.
Finally, take fan cables away from air path and arrange them conveniently by means of cable ties.

For hardware enthusiasts, I'll finish recommending this PappaLitto's thread:
https://www.gpugrid.net/forum_thread.php?id=5006

Another tip regarding fans topic, and their frequently associated heatsinks:

It is advisable to maintain them from time to time, to release stacked dust, fibers, and pet's hair.
Not doing this will cause a progressive worsening in heat dissipation, and thus a gradual tempereture rising in whole system.

For this task I have three different tools:
-1) A 20 mm width common painter brush
-2) A hair dye brush. My wife gave it to me, and I quickly found its utility...
-3) A mini vacuum-cleaner


For cleaning heatsink fins, and gaps in between, hair dye brush is the most useful tool I've ever used. I can recommend it.
Painter brush's bristles are not rigid enough to enter gaps between heatsink fins easily. Hair dye brush does it.
You will undestand what I say taking a look to this photo:


However, painter brush is a very convenient tool to clean fan blades, flexible and smooth enough to do the job properly:


If after cleaning the system you start to hear a loud (awful) noise... Oh, oh, please, refer to first post in this thread...

Regarding heat dissipation, laptops should be considered as an apart subgroup.

Normally laptops are manufactured prioritizing other guidelines than easy-to-maintain one.
Here is a picture of a common laptop hardware distribution:


For space reasons, laptop's heatsink usually is very compact, and it has to dissipate heat coming through heatpipe from CPU and GPU, with the help of forced air impulsed by system fan.
Working laptops get warm, becoming irresistible for any surrounding pet...
And here is what can be found if you manage to dismount the fan:


In this situation, heat is not efficiently dissipated, and the whole laptop may overheat.
GPU and CPU, usually the most power consuming components, become hot spots inside, and in worst case may fail due to overheating.

Some advice if crunching in laptops:
- Try to monitorize temperatures in some way, permanently or at least when laptop's fan becomes louder than usual.
- Set BOINC Manager preference for "Use at most 50 % of the CPUs".
- Please, never lye a working laptop over soft surfaces like blankets, towels, cushions... This will restrict air circulation and cause overheating.
- If there is luck enough for the laptop to survive manufacturer's warranty, consider cleaning heatsink from time to time. But I recognize that in most cases it is an arduous task!

I use XPOWER to blow the dust off my computers:
https://www.amazon.com/gp/product/B01BI4UQK0/ref=ppx_yo_dt_b_asin_title_o06_s00?ie=UTF8&psc=1
____________

Electric leaf blower for the win!

https://www.youtube.com/watch?v=l0ohF6zthOQ
____________
Team USA forum | Team USA page
Join us and #crunchforcures. We are now also folding:join team ID 236370!

Electric leaf blower for the win!

https://www.youtube.com/watch?v=l0ohF6zthOQ

I use XPOWER to blow the dust off my computers:

A point to consider when using"Blower" devices is Electro Static Discharge.
Ensure the device is NOT made of PVC/PET based plastics. Otherwise you risk the destruction of your electrical equipment through Electro-Static Discharge.
There are a number of ESD safe Blowers available, but tend to be more expensive due to the plastics used.
One example here: https://www.amazon.com/Canless-System-Hurricane-ESD-Safe-Replacement/dp/B00CJHGLFK

A point to consider when using"Blower" devices is Electro Static Discharge.
Ensure the device is NOT made of PVC/PET based plastics. Otherwise you risk the destruction of your electrical equipment through Electro-Static Discharge.

Another relatively common situation, mainly in veteran rigs (like mine ones):

You stop your usually 24/7 crunching rig for a preventive hardware maintenance, or it suddenly stops due to a power outage.
When you start the system again, it stops with a message indicating some data corruption - memory checksum failed.

What's happened?
When system is connected to the mains, PSU will permanently deliver a +5VSB voltage, even if system is switched off.
This voltage feeds the volatile memory chip storing BIOS setup, real-time clock, and system start related electronics.
When system is not connected to the mains, there is still a reduced part of the mainboard maintained by a battery, usually a 3V CR2032 button one.
This battery maintains energized the real-time clock and BIOS setup memory chip.
If battery becomes exhausted, real-time clock will stop, and memory data will probably get corrupted.
Solution to this problem is very easy: Replacing exhausted battery by a new one.

To do this I use the following tools:
-1) A flat head mini screwdriver
-2) A fine point CD marking pen


Disconnect system from power and briefly press Start button. This will discharge any voltage remaining at PSU.
Locate backup battery at mainboard and take note/photo of original +/- polarity in its socket.
Unpack new battery and annotate current month/year over it on its "+" side with CD marking pen. Doing this, You will prevent confusing old an new batteries, and it will serve as "maintenance logbook".
Press carefully with screwdriver the old battery's retention latch while maintaining your other hand's thumb over the battery. Battery sometimes may bounce, as bottom terminal acts as a spring.


When battery is lifted, grasp it and take away.
Set new battery on the socket respecting original polarity, and press it until retention latch clicks in place.


Reconnect power, start the system, enter BIOS setup, reconfigure parameters and date/time, and exit saving changes.

A true case more to share:

Yesterday I left a laptop normally processing a MilkyWay@home CPU task. OS: Ubuntu Linux.
Today, WU was finished but not reported by BOINC Manager.
Entering system configuration, I got a message about it was not installed any WLAN adapter.
But yes, it is installed! (Unless it has gone to a party overnight...)
Definitively it is installed, and I can prove it.



It is the one remarked in red in above image...
This is a typical case of bad electric contacts between a component and its socket.
Now my laptop is normally working again, the stalled task was reported, and a new one was downloaded and is in process.

What was the solution?
I extracted card from its socket, treated contacts, reinserted it, and it returned to work.
For this, I used a technical drawing's rubber for pencil and small brush.
I've gotten a pencil rubber not too soft, not too hard in a thecnical drawing shop.
This rubber has an ink side too, but it is not advisable to use it in delicate contacts, as them might became scratched.
Taking a careful look to following image you would be able to distinguish between narrower side of contacts (already treated) and broader side (not treated yet):
http://www.servicenginic.com/Boinc/GPUGrid/Forum/WLAN_02.JPG

Other typical problems caused by bad electrical contacts:

Symptom: Component not being recognized (as present case was)
Remedy: Extract component, clean contacts and reinsert.

Symptom: A GPU normally working fine starts to fail tasks intermitently with no apparent reason.
Remedy: Extract GPU and memory DIMMs, clean contacts and reinsert.

Symptom: There is no image at system start, or starting even stops with some combination of loud beeps.
Remedy: Extract GPU and memory DIMMs, clean contacts and reinsert.

Symptom: System intermitently stops with blue screens, or restarts with no apparent reason. It may be caused by some intermitent RAM memory corruption.
Remedy: Extract memory DIMMs, clean contacts and reinsert.

PLEASE, PAY ATTENTION

- All those components are electrostatic sensitive. Lay them over an antistatic surface. Those silver shining bags containing mainboards or graphics cards are suitable for this.
- Allways switch off computer, disconnect from mains, and ensure no residual voltages are present (I.E. some led is still lit in mainboard). Usually, you can prevent this by pressing computer's start button briefly once it is disconnected (I.E. all leds will immediately extinguish)
- Touch some metallic part of computer's case to discharge you from static charges before touching any inside component.

Fantastic, detail description of troubleshooting and repairing. I like the idea of the pencil rubber to clean the contacts.

- Allways switch off computer, disconnect from mains, and ensure no residual voltages are present

Touch some metallic part of computer's case to discharge you from static charges before touching any inside component.

The only thing different I would do (assuming building power and cabling integrity is in good order):
Turn off power at mains and leave power cord plugged in the wall. The earth connector on the power lead will allow for static discharge to be earthed to the building earth when you touch the case. Touching the case to discharge static electricity will not work as well without the plug in the wall.

I would recommend using an Anti-Static ESD grounding mat kit with a wrist strap and the proper grounding connection to the wall outlet.

These are much better and safer for your equipment and yourself. It will also protect your work surface from damage.

Here is a link to a fairly inexpensive one for the UK or EU. It doesn't have a full metal wrist strap however it would be adequate for most uses.

https://pcvalet.co.uk/Buy/Anti_Static-ESD-Grounding-Earth-Mat-Kit%2C-500-x-400mm-%2F-UK-or-EU

I would recommend using an Anti-Static ESD grounding mat kit with a wrist strap and the proper grounding connection to the wall outlet.

I have a portable ESD field service kit. The mat folds and fits into a pouch along with the other items. The kit also fits into my laptop bag.

It is similar to this one.
https://www.tequipment.net/Prostat/PPK-646/General-Accessories/

This one is a bit more expensive so you may need to shop around for a better price.

Choosing the right Power Supply Unit (PSU).
Or how a few minutes of thinking can save a lot of money and wasted energy.

Hypothetically: I am designing a self made computer, and I choose the most powerful PSU I can afford. Right?... Not necessarily!
I must choose the most efficient PSU I can afford, according to computer global charasteristics.
This will save money in my electric bill and heat emitted to environment. (Please, revert terms, if you prefer)

Let's imagine a practical example:
One system is consuming 800 effective Watts, but it is demanding 1000 Watts from AC power outlet.
This 20% of lacking is wasted power, and therefore this particular PSU is being 80% efficient.
Whatever we can do to increase this efficciency, is well done.

Two main considerations:
-1) Try to choose an 80% or better efficiency certified PSU. You'll soon amortize the extra inversion in your power bill.
-2) Try to accomodate the PSU maximum rated power to about double the one demanded by your particular system.

Explanation:

-1) Please, take a look to following table:

It is taken from Cooler Master PSUs manufacturer webpage.
Picture shows an increasing efficiency PSU classification.
The more efficient, the more fine tuned and quality must be electronics, larger copper sections, optimized Power Factor Correction (PFC) circuitry... and usually it means a more expensive final product.
But as already said, it is going to self-amortize with time.

-2) And taken from the same manufacturer webpage (*), a typical efficiency curve representation.

Typically, a PSU is peaking its maximum efficiency when it is delivering about half its maximum rated power.
It can be seen by watching the Efficiency-Load curve.
But yes, you have deduced right: Efficiency decays drastically at low loadings.
In few words: If I select a 1500 Watts PSU to feed a 150 Watts low power consumption system, in some way I'll be wasting my inversion!
At following link is featured an application form to calculate maximum power demanded by a system.
https://www.coolermaster.com/power-supply-calculator/
This is calculated for all components consuming their maximum power concurrently. This is not an usual situation (unless you are processing ACEMD3:-)
For example: For a calculated maximum power of 400 Watts, I would choose a 750 Watts PSU. This would make PSU working at its maximum efficiency, and even some margin would left for future hardware upgrades.

(*) https://www.coolermaster.com/catalog/power-supplies/v-series/v850-gold/#overview

A totally or partially defective PSU may cause a wide variety of problems at affected computer:
- System stopped and not responding at all to 'Power on' button
- System starting and switching off in few seconds in an endless loop
- System intermitently switching off or rebooting itself
- Applications failing intermitently, specially high power demanding ones
- System overheating if PSU fan fails
- Motherboard or peripheral components breakage in severe cases

PSU delivers several voltages to electrically feed computer's motherboard and peripherals.

Taken from the manual of a Gigabyte motherboard, voltages and signals coming from PSU are as follows:


Taken from an Aerocool modular PSU, Connectors functions and shapes are as follows:




Given a certain PSU, every voltage has its associated maximum rated current and power.
Taken from the same Aerocool PSU, a typical specifications label is as follows:


Replacing a PSU is more laborious than difficult.
The steps:
-1) Switch computer off, and disconnect PSU from power outlet.
-2) Wait some minutes for PSU capacitors to discharge, or force it by pressing briefly computer's 'Power on' button.
-3) Take note/photo of all the previous PSU connections: Motherboard, CPU, Hard disk(s), Optical unit(s), Graphics card(s), Peripherals, cooling devices...
-4) Disconnect all those connectors. For some of them it will be necessary to press some fixing latch while pulling up.
-5) Check all cables coming from PSU to be free. Cut carefully fixing ties if exist.
-6) Unscrew PSU fixing screws, normally four of them placed in the same PSU's face than AC power connector.
-7) Extract replaced PSU from its position, being careful for not to hit other computer components. For this, sometimes it will be necessary to extract other components as CPU cooler, optical unit, graphics card... if they block old PSU extraction and/or the insertion of the new PSU.
-8) Insert new PSU in place, and fix it with its screws. For this, see final tip (*)
-9) Reconnect all connectors previously listed in step (3). Be careful to double check full insertion for all connectors. Some of them must be pushed until fixing latch clicks in final position. Specially motherboard's 20+4 pins connector may be hard to insert. If possible, try to support at motherboard's back while pushing, for not to overstress it.
-10) Arrange all cables by means of cable ties to convert the original cable mess into a more air-flux-friendly combination.
-11) Test the system for a correct start up. For this first time, it is advisable to enter BIOS setup and check in Motherboard's System Monitor for all voltages being into specifications.
-12) Replace covers (if any), reinstall system at its usual placement, and that's all.

(*) Tip:
GND rail delivers return for the addition of all voltage rails currents.
PSU's GND rail is directly connected to its metallic chassis and to electrical protective earth terminal.
Also Motherboard's GND is connected to all fixing holes on it, and from them to computer's chassis.
The better electrical contact between PSU and computer's chassis, the less the voltage drop will be due to current circulation.
For example, a contact resistance as low as 0,01Ω causes a voltage drop of 0,4V at a circulating current of 40A.
40A is about the current demanded to +12V rail by two GTX 1080 Ti or RTX 2080 Ti cards.
If contact resistance is increased, also increases the chance to cause problems: overheating, burnt contacts, Intermitent computer errors, intermitent system rebooting...
Something as simple as selecting the best PSU's fixing screws, may help to decrease electrical resistance between PSU and computer chassis, and help a bit to conduct returning current.
The best ones are the stepped backhead screws shown at leftmost of following picture. Varnished (rightmost) screws are probably more beautiful, but varnish may worsen conductivity.

Great post!
Nice tip about the fixing screws, now I have to go and check all my fixing screws...

When replacing modular PSUs:
Keep in mind that the PSU end of the modular connectors are *NOT* standardized!
You have to carefully compare the PSU end pin-out of the old and the new PSU (especially when they came from different manufacturers), and if there's any difference between them then you must remove the old cables also (not just the PSU). It is advised to remove the old cables anyway, as their contact resistance grows over time due to corrosion.
The branding of the PSU and the actual manufacturer of the product is not the same thing. So you can buy the same brand and the PSU end pin-out still could be different.
A good source of info about PSUs:
https://www.jonnyguru.com/

When replacing modular PSUs:
Keep in mind that the PSU end of the modular connectors are *NOT* standardized!

A good source of info about PSUs:
https://www.jonnyguru.com/

There are specific tools to easier diagnose PSUs, as the one shown below.
PSU Tester
To on-bench diagnose, it is enough to connect the 24 pin connector, one 4 or 6 or 8 pin connector, and one SATA connector.
When switching PSU on, tester will automatically start it, and show the different voltages.
Also delay between +12V on and 'Power Good' signal is shown.
Abnormal voltages are those outside -5%...+5% for +12V, +5V, +3.3V and +5VSB.
The -12V is more tolerant, and is considered normal in the range -10%...+10%
Normal values for PG delay are in the range 200...500 ms

- If PSU Doesn't start when switching on and correctly connected, probably it is dead and in the need to be replaced.
- If any voltage is missing or outside tolerance, PSU needs to be replaced.

VERY IMPORTANT
If on-system PSU testing is made, it will be necessary to disconnect ALL PSU connectors from motherboard and peripherals. Please, double check this!
As soon as this kind of test will bring power to every connectors, damage to system may occur if any of them is left connected.

Althoug a faulty parameter indicates the need to replace the PSU, a passing PSU may be still defective.
The reason: This kind of tests are made at very low currents compared to a system running at maximum performance.
Running at higher currents may cause a parameter to fall ouside tolerance.
Also some problems are caused by failing components when heating.
And some intermitent problems might not be catched in such a brief test...

I have recently read about a special thermal "grease".
It is actually a special metal compound which is liquid at room temperature like mercury (but it's not made of mercury).
Its thermal conductivity is 6-10(!) times higher than of a usual thermal grease (73W/mK vs 8.5W/mK).
See the manufacturer's page for reference:
Thermal Grizzly Conductonaut
I haven't tried it earlier, as it has a serious negative side: this metal compound (like most of the metals) conducts electricity as well as heat.
So it must not get out of the chip's surface as it will result in a short circuit which breaks the GPU or the CPU (or the MB) for good.
It should not be applied to aluminum heatsinks.
But if you are experienced, have the time and patience to thoroughly clean the surface of the heatsink and the chip (or the IHS) with alcohol (I had to even use polish paper on one of my heatsinks), and carefully apply as less of this thermal compound as possible (to avoid the excess metal go where it shouldn't) then you can have a try with this product.
The result will worth the time and effort:
On my single GPU systems I experience
· 10-15°C (!) lower temperatures at the same fan speed.
· 30-50% (!) lower fan speed at the same temperatures.
The better the heatsink, the better the result.
You can choose how to balance between these by your fan curve.
The factory settings will result in slightly lower (3-5°C) temperatures at a much lower fan speed.
Of course, it can be used to achieve better overclocking as well.
Most of the Intel CPUs have normal thermal grease between the CPU chip and the IHS, so it must be replaced with this product to achieve better results. As this grease is under the IHS (the metal covering the chip to protect it), first you have to remove the IHS, which is glued to the PCB (the green area) which carries the chip. There are professional tools to do this without damaging the CPU. Hopefully I'll have mine next week, and I'll report the results then.

Been using it for about a year now Zoltan for some of my bigger machines with higher thread counts. Was recommended by one of my teammates and never thought about it again. Good information.
____________

See the manufacturer's page for reference:
Thermal Grizzly Conductonaut

Been using it for about a year now

Thermal conductivity specifications for Conductonaut are really impressive.
In the other hand, as you remark, it is contraindicated in live circuits due to its electrical conductivity.
Following image comes from a true thermal paste replacing operation in one of my graphics cards:

As seen in the image, GPU chip core usually is surrounded by capacitors (here remarked by red ellipses). That white compound between many of them is the reamining non-conductive factory thermal paste.
Those capacitors would be shortcircuited if in contact with an electrically-conductive compound...

Another bit of advice for applying Conductonaut:
It is better to apply it on the heatsink to a slightly larger area than the chip, because in this way the excess material will stick to the heatsink.
This compound won't make the copper (silicon, nickel) surface wet by itself, you have to carefully rub it on both surfaces. This way it can be made really thin. You have to start with a very small (pinhead sized) droplet, and rub it on the desired area. If it turns out to be insufficient, you can add a little more (it won't make a droplet if you add it directly to the existing layer, it will add to the thickness of the layer instead).

Now I understand the mechanics for this product.
I appreciate your masterclass very much.
It is always a good time to learn something more!

On my single GPU systems I experience
· 10-15°C (!) lower temperatures at the same fan speed.
· 30-50% (!) lower fan speed at the same temperatures.
The better the heatsink, the better the result.

I've ordered one 1g Conductonaut syringe, and I'm expecting to receive it in less than one month.
I'm curious to test it and report results.

Well, I've received my Conductonaut thermal compound kit this week, and I've already tested.
First of all, my special thanks to Retvari Zoltan, for bringing here this interesting topic.
I'm sharing my very first experiences with it, as I promised.

For this, I've selected this system.
Currently it has two graphics cards installed, one GTX 1660 Ti, running preferably GPUGrid among several other GPU projects, and one GTX 750 excluded from GPUGrid, for delivering video and running all other projects.
This is a BOINC Manager screenshot at the moment of starting preliminary tests.
In that situation, this is a Psensor screenshot for system state.
GTX 750 temperature was 53ºC while running a MilkyWay task, and GTX 1650 Ti temperature was 73ºC while running a GPUGrid task.
Then, I suspended activity in BOINC Manager, and GTX 1650 Ti temperature dropped 47ºC, from 73ºC to 26ºC, in about 8 minutes. Too big and fast temperature fall for me to feel comfortable.
I restarted activity again, and a subsequent temperature raise can be seen from 26ºC to 71ºC.
Such sudden temperature changes suppose a mechanical overstress to GPU due to cantractions and dilations. This might reduce its life expectancy!
So I chose GTX 1650 Ti to test Conductonaut.
This is the same card that was object for this other thread.

I started by dismounting cooler's fans and cleaning them.
Then, I dismounted GPU cooler by unscrewing its 4 spring-loaded mounting screws, and I cleaned it also.
Next step was cleaning thorougly GPU chip, as can be seen in "before" and "after" images.
I managed to carefully remove all thermal paste remains between capacitors by means of wooden toothpicks, and finally cleaned all chip surfaces with isopropanol-dampened cotton swabs.

Now, it's time for Conductonaut release...
Starting with a small drop at the center of cooler's copper core, then gradually spreading it until covering all copper surface.
I payed special attention for not to reach aluminium zones, as Conductonaut is expresely contraindicated for them.
For spreading, synthetic-tissue headed swabs are supplied in Conductonaut kit.
And they work for this purpose better than I expected.
Time now for silicon surface of GPU chip, following the same procedure.

Once surfaces were treated with thermal compound, graphics card was rebuilt in reverse order than dismounted.
Starting with GPU cooler, paying special attention for tight coincidence between Printed Circuit Board holes and cooler's ones.
The best way for me: laying cooler on the table with threaded mounting holes facing up, and then slowly lowering PCB while looking through its holes to a final perfect match.
Then, I remounted the 4 original spring-loaded screws by gradually tightening them, following a cross-pattern iterative sequence.
It is hard to photograph with a domestic camera, but if the proper amount of thermal fluid is used, GPU capacitors are safe apart from contacting it.

GTX 1650 Ti remounted in place, and... did it worth the job?
Comparing the new temperatures with the original ones while running a GPUGrid task, a reduction from 71ºC to 60ºC can be appreciated.
Definitively, it did worth the job.
And I've enjoyed the moments in between!-)

Let's make a small correction to my own previous post: Every times a "GTX 1650 Ti" graphics card is mentioned, it should be GTX 1660 Ti.
"GTX 1650 Ti" is a quimeric mix between GTX 1660 Ti and GTX 1650 models.
I have a couple of GTX 1650 cards also, but I have no such temperature problems due to their lower power consumtion (75 Watts) compared to GTX 1660 Ti (120 Watts)

I've received my CPU IHS remover kit. It's a Rockit-88 kit.
It makes the IHS removal to be the fun part of the whole process.
I've changed the original thermal paste to TGC so far in these CPUs:
i5-8500
i5-7500
i3-7300
i7-4790k
i5-750

I've also changed the thermal paste between the IHS and the cooler to TGC.
The i5-8500 and the i5-7500 runs 11°C lower than before.

It was very hard to clean the i7-4790k chip, the TGC didn't spread on its surface very well. I think I have to do it again.

The i5-750 is a 10 year old CPU, it runs at 78-79°C with the standard Intel (copper core) cooler, while all 4 cores are fully loaded, and the PC is in a micro ATX case (side panel is on). I'll change this cooler to a Noctua D9L, as larger coolers won't fit in this case.

Symptom: PSU's Main switch turned from Off to On, an sparking sound is heard, and overcurrent protection at electrical panel goes down (leaving 4 computers without power, by the way).
Cause: Short circuit in PSU's driver circuit component at HVDC to DC converting stage.
Solution: Replace defective PSU. (I've won in some way by exchanging the old 80+ efficiency PSU by a new modular 85+ one)
Guilty component: It can be seen at this forensics image, marked as IC2 at center of picture.
I like this kind of problems!: Clear diagnose and simple solution

Relative tip: Most PSUs have at AC rectifying stage an NTC (Negative Temperature Coefficient) resistor (thermistor) for limiting switch on current (it can be seen, out of focus at left of above image, lentil-shaped green component).
When this NTC is cold, its base resistance is in series with rectifying circuitry, thus limiting the otherwise high initial charging current for HV capacitor(s).
As the current circulates, the NTC is heating and decreasing its resistance to a near-zero value.
If PSU is switched off and then on in a rapid sequence, there is no time for this NTC to get cold, and its intended current limiting effect is decreased, thus causing a potentially nocive high current peak.
For this reason, it is advisable to wait at least (let's say) 10 seconds from switching off to switching on again the PSU, for this component has enough time to cold.

Relative tip: Most PSUs have at AC rectifying stage an NTC (Negative Temperature Coefficient) resistor (thermistor) for limiting switch on current ...
When this NTC is cold, its base resistance is in series with rectifying circuitry, thus limiting the otherwise high initial charging current for HV capacitor(s).
As the current circulates, the NTC is heating and decreasing its resistance to a near-zero value.
If the PSU is switched off and then on in a rapid sequence, there is no time for this NTC to get cold, and its intended current limiting effect is decreased, thus causing a potentially nocive high current peak.

For this reason, it is advisable to wait at least (let's say) 10 seconds from switching off to switching on again the PSU, for this component has enough time to cold.

An interesting article to deepen about thermistors.
There is an specific section about Inrush Current Limiting Thermistor
Moreover, in most of motherboards, temperatures indicated by hardware monitor are based on thermistor sensors.

An interesting article to deepen about thermistors.
There is an specific section about Inrush Current Limiting Thermistor
Moreover, in most of motherboards, temperatures indicated by hardware monitor are based on thermistor sensors.

If they operate at 80-90°C...

...then 10 seconds is probably enough for them to cool down to 50-60°C, so they will limit the inrush current (not that much if they start from room temperature though).

Reading this post, I thought... This can be a challenge for a hardware enthusiast!
When server is plenty of WUs, everything is wonderful for our hosts with minimal intervention.
But at scarcity periods, I've past many moments clicking "Update" at BOINC Manager for requesting job...
So I asked myself: Is there a way to better employ this time in other tasks?
I rescued some basic engineering concepts, and I spent a funny weekend while developing it.
Now, after testing it to work, I'm pleased to share with those of you interested to try.

I had an old souvenir mouse stored in a drawer. I dismounted it and took as starting point.
Then, I designed the electrical circuit, I gathered the necessary material, and I got to work.
This is the resulting circuit as seen from top.
And this is as seen from bottom.
It is made with a technic I used to employ when I studied, soldering point to point by means of wire-wrapping cable.
Now time to integrate at mouse circuitry and assembly.
And here is the final result.

Does it work as intended?
Yes, it does!
This combination sends an automatic request for tasks about every two minutes.
I've tested it on my fastest crunching-only host, for downloaded WUs (if any) to be returned on the day.

Finally:
As soon as I showed it to my son, he asked me: You know that there are software applications that do the same, don't you?
Yes, I do, but... This is the hardware enthusiast's corner!

Thanks for an enjoyable project tour.

There is much to be said and gained from cobbling a solution together, inelegant though it might be of bits and pieces scrabbled from the bit bucket of cast off parts. At least exercise of the old grey matter was performed.

The problem:
One 24/7 processing computer loosing intermitently its network connection, thus not being able to report processed tasks, nor asking for new work.
The cause:
Its Wireless network card not fully inserted into PCIE x1 socket, resulting in an intermitent bad electrical contact problem.
The solution:
After checking, it was a mere mechanical problem.
It was corrected by dismounting the card from its mounting frame, and bending the fixing tabs in the proper (CW) direction.
As a result, the whole card was tilted in the direction of fully insert into PCIE x1 socket.

In line with my last post:

A graphics card without extra power connector(s) is receiving all its power from the PCIE socket.
For example, this GTX 1650 rated TDP is 75 Watts, and it has no power connectors.
This requires a current of 6,25 Amperes from the +12 Volts supply. (12V x 6.25A = 75W)
For this reason, it is particularly important for this kind of cards the best possible electrical contact into PCIE socket.
Usually there is enough mechanical play at Graphics cards mounting frame to physically reseat its PCB to be deeply inserted into PCIE socket.
In my experience, this mechanical play can vary from about 0.5 to 1.5 milimeters (0.02 to 0.06 inches).
It is usually very easy, and it takes only a few minutes to reseat PCB this way.
Taking the same above mentioned graphics card as an example:
This is how its mounting frame looks like.
I'll loosen all frame's fixing nuts/screws.
Starting with the two hexagonal female-threaded nuts, marked as 1 and 2 in previous image, then finishing with all screws, here marked as 3 and 4.
Depending on the kind of card, there may be a lower or greater number of fixings, but usually they are easy to locate.
Once all fixings are loose, the mounting frame will show its mechanical play.
Holding PCB at its deeper position relative to mounting frame, all fixings are to be retightened now, starting again with the threaded nuts (here 1 - 2) and finishing with all screws (here 3 - 4).
The final result: Graphics card PCB has come down nearly 1 milimeter.
It can be appreciated when looking at Before and After images.

In a computer where its graphics card is intermitently being unrecognized, this could be a point to discard.

If keen on bricolage and informatics, how about mixing both?
I'm explaining a good example for this.

The only fan for this GTX 1650 graphics card started to fail, and I retired it momentarily from work to avoid it to become damaged due to overheating.
I asked myself: Should I claim for warranty, and wait perhaps a couple of weeks for the new card to arrive... and lose the fun for solving it by myself?
I doubt for about 10 seconds. This is self answered in this post.

I looked for something to help among my retired cards, and I found this Gigabyte GT640 GV-N640OC-2GI that I probably would not use any more.
I like Gigabyte cards because of their usually good design, constructive quality, and well dimensioned heatsinks and fans.

Comparing heatsink mounting spacings in both cards I found to be nearly identical. And Gigabyte heatsink's surface and fan were bigger than original PNY's ones (Ok!).
But comparing the components layout below heatsinks, some problems arised.
Gigabyte's heatsink was hitting several PNY's card components: One quartz crystal (Y1), one solid capacitor (C204), and one ferrite core choke (L15)
Here is when the bricolage part comes in play...
- Marquetry saw for metal cutting, to retire some problematic fins.
- Minidrill with ceramic milling piece, to make space into aluminum where needed.
And mechanical problems are solved.

Now it's time for applying [url=http://www.servicenginic.com/Boinc/GPUGrid/Forum/HE/GpuCoolerReplacement/06_Thermal paste.JPG]thermal paste[/url] and heatsink assembly.

One more adapt was needed, because fans connectors were not compatible. But a bit of soldering and heat shrink sleeve, and also it's solved.

After this, we can compare between Before and After .

Now this peculiar hybrid PNY-Gigabyte graphics card is working again!

A final question for users that may have experienced a similar situation: Is fan usually covered by card's warranty?
If so, is the whole card replaced by distributor, or the fan only?
Your experiences at this respect would be very appreciated.

Does this card run at a lower temperature than before?

One more adapt was needed, because fans connectors were not compatible.

A final question for users that may have experienced a similar situation: Is fan usually covered by card's warranty?

If so, is the whole card replaced by distributor, or the fan only?

Does this card run at a lower temperature than before?

The original card doesn't have a 3rd pin (tachometer), so the card can't sense if the fan is not rotating.

...they will replace it. But the replacement will be the same quality, so I usually replace the fans (or the complete heatsink assembly) for a better one.

As of current restrictions in many countries due to COVID-19 impact:
It becomes important to solve our hardware problems by ourselves.
Please, feel free to share here your problems in a Symptom - Cause - Solution scheme, or your favorite self-learnt tricks.
It may be of great help to other colleagues.
Thank you in advance!

- Symptom: A computer controlling an important process suddenly switched off by itself. Repeated attemps to switch it on again resulted in switching off after a few seconds past.

- Cause: Two Processor heatsink's fixings had broken, causing it to tilt and loss tight contact with processor surface. As a self-protecive measure, system is switching off to prevent processor damage due to overheating.

- Solution:

* Plan A:
First attempt consisted of repairing the broken fixings with fast curing cyanocrilate glue.
After two hours curing, time to renew processor's thermal paste and reassemble heatsink.
Result: After about three minutes waiting, fixing springs overcame glued parts and they got broken again.

* Plan B:
Studying carefully the heatsink mounting hardware, there was a passthrough hole at every corner in a very suitable placing to solve the problem by means of strategically arranged cable ties.
Result: Cable ties are strong enough to keep necessary tension. Problem solved, and everything is working again!

Particular conditions for this case:
This case comes from a true intervention in the PC controlling a laboratory diagnostic instrument for celiac and autoimmunity diseases.
I had to carry out this intervention dressed in all necessary PPEs (Personal Protective Equipments), thus not being fully free to go and come for spare parts.
Solving the problem meant that diagnostic results for many patients, otherwise lost, were successfully retrieved.
I took it as a NOW or NEVER situation, and happily it was NOW.

Finally: Let this be my modest tribute to all those worldwide medical staff and field service colleagues, currently working in hard conditions due to Coronavirus crisis.

Finally, my adventure with Conductonaut thermal compound ended in an unexpected way.

For background, please, refer to my previous post dated on January 26th 2020.
On past March 29th, while a regular round of temperature checks, I found that the concerned GTX 1660 Ti card's temperature was 83ºC. (!)
Yes, it was running an ACEMD3 WU, but when I first tested Conductonaut this temperature was 60ºC...
I dismounted the GPU's heatsink and found that the original liquid-metal Conductonaut's state was converted in a soft-solid metal state.
On this new state, I observed some cracks and irregularities, explaining a bad thermal coupling and subsequent abnormal temperature raising.
It was hard to retire the altered compound, first using a plastic spatula, and then a fine polishing cotton.
I can reccomend this kind of silver cleaner, made of a fine polishing-compound impregnated cotton.
At the end, heatsink's copper surface recovered its original appearance.

I decided to replace Conductonaut using my regular non-conductive thermal paste, Arctic MX-2.
Manufacturer promises an eight years durability for it.
Based on my own experience, I've tested to last at least 4 years, because I usually prefer to preventively replace it after about this period.
It is easy to apply, due to its self-spreading ability.

After this, GTX 1660 Ti returned to work, now the temperature being reduced from previous 83ºC to 77ºC.

In a 24/7 working rig, it is advisable to check temperatures in a regular way, to prevent overheating on different components.
For sure, it will increase the life expectancy for the whole system.

Thermalright TF8 Thermal Compound Paste is the best I've used. It has the highest thermal conductivity at 13.8 W/mK. The best thing about it is that when you remove the CPU cooler after months of use it's still gooey and hasn't solidified like most others. It's the most expensive, until competition comes along. One wants the thinnest continuous layer you can get so use as little as possible and use the spatula to spread it out. I expect it can last for years.

https://www.amazon.com/gp/product/B07K442WXV/ref=ppx_yo_dt_b_asin_title_o08_s00?ie=UTF8&psc=1

Finally, my adventure with Conductonaut thermal compound ended in an unexpected way.

For background, please, refer to my previous post dated on January 26th 2020.
On past March 29th, while a regular round of temperature checks, I found that the concerned GTX 1660 Ti card's temperature was 83ºC. (!)
Yes, it was running an ACEMD3 WU, but when I first tested Conductonaut this temperature was 60ºC...
I dismounted the GPU's heatsink and found that the original liquid-metal Conductonaut's state was converted in a soft-solid metal state.

This is very strange. I didn't experienced such change in the liquidity of the Conductonaut...

Derived from current COVID-19 regulations at Spain, requiring home confinement, a challenge arose:
Will I be able to build a new crunching rig from my stored spare/scrapped pieces?

I started by rescuing an ancient Pentium 4 system "stored" at top of a wardrobe.
I dismounted motherboard, PSU, peripherals, and I got that old minitower ATX chassis as starting point.

PSU: The old PSU had not proper connections for current mainboards.
I rescued two PSUs from my scrap drawer, one with failed electronics, and the other with failed fan...
I replaced defective fan by the working one, and the PSU problem was solved.

Motherboard, CPU, RAM: I had stored at spares drawer the ones leftover from my last hardware upgrade.
There was a new problem: Available chassis is an old model one, with PSU hanging directly above CPU location. But I found an original Intel low profile CPU heatsink, and problem was solved also.

From spares, I rescued my last remaining 120 GB SSD and a GIGABYTE GTX750 factory overclocked graphics card...
With all these and a bit of (free ;-) self-workmanship, the new rig is a fact without leaving home: Test passed!

New system Host ID: 540272

New system look:

One more detail: Due to the low power consumption (38 W TDP) graphics card and the reduced CPU heatsink, this is the only of my rigs with CPU running hotter (59 ºC) than GPU (53 ºC) at full load.

If we call severe to a problem that prevents a computer to start working.
If we call ridiculous to a trivial circumstance causing a severe problem.

This is one of the most severe-ridiculous problem I've ever found, and more than once.
It happened today in one of my rigs.
I'm documenting it this afternoon, and I'll publish the solution on tomorrow's afternoon.

- Symptom: Starting the system, it runs for some seconds, then it stops and nothing happens on following attempts to restart.
I opened this system, I made a quick contacts check, started again, and this time the start attempt succeeded (Fans turning, beep heard...) for a few seconds only.

- Cause: I started to think: PSU failure, CPU heatsink disengaged... and, If it was...? And it was it!

- Solution: ???

You have 24 hours to guess your favorite cause-solution.

A stuck power button can cause this: first it turns on the system, but if it stays in the "pressed" state it will turn off the system after 4-5 seconds (hard power off).

Bad PSU
Bad motherboard
Bad memory
____________

Bad PSU
Bad motherboard
Bad memory

- Symptom: Starting the system, it runs for some seconds, then it stops and nothing happens on following attempts to restart.
I opened it, I made a quick contacts check, started again, and this time the start attempt succeeded (Fans turning, beep heard...) for a few seconds only.

A stuck power button can cause this: first it turns on the system, but if it stays in the "pressed" state it will turn off the system after 4-5 seconds (hard power off).

finally I was able to finish up my newest GPUGRID system. It's one of my old SETI systems, but I needed to convert it from USB risers to ribbon risers (and motherboard swap) for the increased PCIe bandwidth requirements here.

CPU: Intel Xeon E5-2630Lv2 (6c/12t,2.6GHz)
MB: ASUS P9X79 E-WS
RAM: 32GB (4x8) DDR3L-1600MHz ECC UDIMM
GPUs: [7] EVGA RTX 2070
PSUs: 1200w PCP&C + 1200W HP server PSU






went with a 2U supermicro active CPU cooler so I had enough room for the ribbon risers on the 2 GPUs above it. replaced the 60mm fan on it with a Noctua one since even at 20% speed the stock fan was very noisy. the Noctua fan doesnt cool as well as the stock server fan that came with it, but it's enough for this 60W chip (temps in the 50's @65% load) and it's a lot quieter.
____________

🙌

I'm really impressed watching at your systems.
Thank you very much for your Masterclass.
That's what I would describe as high-level computer hardware engineering.
And your just newborn system is returning processed tasks like a charm...🙌
Congratulations!

finally I was able to finish up my newest GPUGRID system. It's one of my old SETI systems, but I needed to convert it from USB risers to ribbon risers (and motherboard swap) for the increased PCIe bandwidth requirements here.

CPU: Intel Xeon E5-2630Lv2 (6c/12t,2.6GHz)
MB: ASUS P9X79 E-WS
RAM: 32GB (4x8) DDR3L-1600MHz ECC UDIMM
GPUs: [7] EVGA RTX 2070
PSUs: 1200w PCP&C + 1200W HP server PSU






went with a 2U supermicro active CPU cooler so I had enough room for the ribbon risers on the 2 GPUs above it. replaced the 60mm fan on it with a Noctua one since even at 20% speed the stock fan was very noisy. the Noctua fan doesnt cool as well as the stock server fan that came with it, but it's enough for this 60W chip (temps in the 50's @65% load) and it's a lot quieter.

Impressive. Thanks for the photos and description.

Great Googly-Moogly! You rule, Retvari!
As Ray Wiley Hubbard says: "Some things here under Heaven are just cooler 'n Hell".

https://www.youtube.com/watch?v=o6C579hWdsI

Maybe name your creation something like Chico Grosso?

he was quoting my post but fixed the hyperlinks for the images. I forgot that this site breaks urls that already include http in the link in BBcode.
____________

On April 20th 2020 | 19:48:27 UTC Ian&Steve C. wrote:

finally I was able to finish up my newest GPUGRID system...

😳 Oops... sorry guys. I was so busy drooling over the rig that I forgot to read the header.
Anyway...
That has to be the best design yet for a crunching machine. You've changed my thinking about what my next opus should look like. Thank you for sharing your expertise with us.

😳 Oops... sorry guys. I was so busy drooling over the rig that I forgot to read the header.
Anyway...
That has to be the best design yet for a crunching machine. You've changed my thinking about what my next opus should look like. Thank you for sharing your expertise with us.

1. Be mindful of the specs of your system, in particular the link width and generation of your PCIe slots. Some slots might be x16 size and fit a GPU, but only have electrical connections for a x8 or x4 link. some older boards might have a mix of PCIe 3.0 slots and pcie 2.0 (half speed) slots. Some motherboards may disable certain slots when others are in use. Pay attention to where the lanes are coming from and where the bottlenecks are. One common thing I see people overlook are the lanes coming from the chipset. It may be able to supply many lanes, but the chipset itself then only has a PCIe 3.0 x4 link back to the CPU. Read your motherboard manual thoroughly and lookup the specs of your components to understand how resources are allocated for your board.

2. GPUGRID requires a lot of PCIe bandwidth, and that likely scales with GPU speed. I've measured up to 50% of a PCIe use on a PCIe 3.0 x8 link, or up to 25% of a PCIe 3.0 x16 link with my RTX 2070 and 2080 cards. If you have a fast GPU, I would not put it on anything slower than PCIe 3.0 x4 (not common anyway) or PCIe 2.0 x8. slower GPUs might get by on slower links.

3. Be mindful of how much power you are pulling from the motherboard. When using USB risers you do not have to worry about this since power is supplied from external connections. But a setup like mine is pulling some of the GPU power from the motherboard slots. My motherboard has a 6-pin VGA power connection to supply extra power to the motherboard PCIe slots. PCIe spec for a x16 slot is up to 75W each! but most GPUs won't pull that much (except 75W GPUs that do not have external power!). If you plug GPUs directly to the motherboard, or use ribbon risers like I have, I wouldn't recommend using more than 3, maybe 4 GPUs (pushing it) unless you are supplying extra power to the board somehow.

4. if on a PCIe 3.0 link, you'll want to get higher quality shielded risers. PCIe 3.0 is a lot more susceptible to interference and crosstalk in the data lines than PCIe 2.0 or 1.0. The shielded risers are a lot more expensive though. I bought what I consider to be "good enough" knockoffs and they work perfectly fine, but were still $25 each, and that's kind of the low end of the pricing for 20cm long risers. out of 14 of these brand risers that I've purchased, 2 were defective (bad PCIe signal quality causing low GPU utilization and GPU dropouts) and needed to be replaced, so test them!

I took all of these things into account to end up with what you see here :)

I have power limited all GPUs on this system to 165W (175W stock), and at full tilt the system pulls 1360W from the wall.
____________

Wow thanks a million! Info I will definitely use.

Im Running V8-XEON built in May 2013 by myself.
Board Intel Skulltrail D5400XS. (2PCI, 4 PCI-E x16, 4 FB-DIMM, Audio, Gigabit LAN)
RAM 16GB FB-DIMM, Quadchannel, Kingston
Processors 2 x E5405 Xeon. LGA771
Grafik 3x EVGA Geforce GTX Titan, (before 2 GTX 470 + 1 GTX 570)
PSU LEPA 1600W continuous Power, Gold certfied

If runs empty, V8-Xeon pulls 285 Watt out of the wall.
If it is crunching on all GPUs it pulls 860 - 890 Watt
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
I shreddert 2 Super Flower PSU 1000W After one and a half year.
The machine is absolut stable. The Xeons run over years with 100% CPU usage.
Old but fine..
____________

Im Running V8-XEON built in May 2013 by myself.

One of my best headless computers was giving me a lot of trouble. Intermittently it would just stop crunching but still be powered up. Sometimes rebooting would get it going again, for a while anyway. So I put it on my desk with a monitor and started swapping power cables and RAM. Then it failed while I was watching and the GPU lights came back on even though I had --assign GPULogoBrightness=0 active in the NVIDIA X Server Settings startup program. At the same time the fans went to max even though it wasn't hot. So I pulled the GPU card to try another and the locking clip on the back of the PCIe socket popped off. I got a flashlight and was trying to figure out how to reinstall the clip when I noticed dirt inside the slot on the contacts. EVGA cards are notorious for having this clear fluid ooze out and sometimes drip down on the motherboard. I assume it's a thermal compound but don't know. It seems to be nonconductive and I've had it on the card contacts before without stopping it from working. I always wipe the card clean when I take them out. But this time I looked in the female PCIe slot with my magnifying glass and saw the contacts were coated with a dusty grime that was mixed in this mystery fluid. I took a toothbrush and cleaner the slot out and then blew it out. Put the same card back and so far so good. One more thing to add to the troubleshooting list.

Another computer would randomly turn off. Sometimes rebooting got it going for a while. When taking it apart the 8-pin CPU power connector to the motherboard had one corner pin disintegrate when I pulled the plug out. It had been running trouble free for years but the plastic of the connector got brittle. Cleaned the connector on the MB out with an X-ACTO knife, turned it upside down and blew it out. Installed a new CPU power cable and it's good as new again.

The "mystery" fluid that oozes out of graphics cards is the silicon oil separating from the thermal pads on the VRM and memory chips or the from the thermal paste.

I noticed dirt inside the slot on the contacts. EVGA cards are notorious for having this clear fluid ooze out and sometimes drip down on the motherboard. ...
It seems to be nonconductive and I've had it on the card contacts before without stopping it from working. I always wipe the card clean when I take them out. But this time I looked in the female PCIe slot with my magnifying glass and saw the contacts were coated with a dusty grime that was mixed in this mystery fluid.

On May 1st 2020 | 1:14:34 UTC Aurum wrote:

One more thing to add to the troubleshooting list.

1. Silicone oil, that makes perfect sense. I was tempted to turn the MB upside down and spray the slots with either isopropyl alcohol or brake cleaner (methanol, toluene, acetone & CO2). Thought better of it since the solvents might dissolve the phenolic or epoxy resin and my board would disintegrate in my hands :-)

The brake cleaner can has a warning: Electrical Shock Hazard: this spray will conduct electricity, keep away from all electrical sources. Imagine doing your brakes one evening with the drop lamp hanging in the wheel well and it's the last thing you ever see.

But seriously, my toothbrush was not a very good way to clean goo out of a little slot. Suggestions welcome.

2. I'm running full steam on Rosetta CPU WUs waiting for OpenPandemics to kick off. Rosetta needs about 1 GB RAM per WU. I've been frustrated with MBs that won't run multiple sticks of RAM. I've been trying to get 64 GB on my 40t & 44t CPUs but only one MB lets me run 4 x 16 GB even when they're the same. I've tried every combination I could. E.g. MSI X99A Gaming 9 ACK, MSI X99A Raider & MSI X99A SLI will only acknowledge 3 x 16 GB. But an MSI X99 SLI Plus will run 4 x 16 GB.
At first I thought it was a bad slot but then I could move the third stick to other array and it would work: DIMM slots: 1, 5 & 3 or 1, 5 & 7.
I bought these cheap on fleaBay so maybe gamers overclocked and overtaxed them and I'm dealing with cripples.

3. The best MB I've got is the cheapest: Huananzhi X99-8M Gaming.

4. Some MBs just won't run the full range of CPUs their specs claim. E.g., my MSI X99A SLI Plus has chronic intermittent stoppages with a Xeon E5-2673 v4 SR2KE but runs flawlessly when replaced with an i7-5930k SR20R. Maybe it's too old and just can't lift the weight any more, like me :-)

I've always found that not reading all the sticks of installed memory on Intel LGA socket motherboards is due the cpu not being inserted correctly in the socket.

Or bent out of place LGA pins in the socket or are overheated. The cpu needs to be correctly located in the socket and also the locking clamp and cooler need to be installed to the correct torque specifications.

The pins in the LGA socket undergo both lateral and vertical position displacement when a cpu is installed. The LGA socket in location is actually very tight. The pins and pads on the cpu need to maintain 40 micron absolute positional location to be within spec.

The notches in the cpu substrate that locate the cpu in the socket allow for a lot of slop. When I don't read all the channels in the installed memory. I always undo the socket clamp and wiggle the cpu in the socket to allow the LGA socket pins to orbit around and hopefully mate with the corresponding pad on the substrate. Then reclamp and test for all the memory to be picked up again.

If you look at the more recent Intel cpu pin mappings, you will find the outside perimeter of pins often contain the memory channel assignments. And those pins undergo some of the greatest positional translation when under compression.

I'm seeing X99 motherboards (e.g. i7-6950X or Xeon E5-2673 v4) that use DDR3 RAM or both slots for DDR3 & DDR4 to be used in an either/or way. My first reaction is what a nice way to get some more mileage from my old DDR3.

Is there a technical reason that combining DDR3 memory with the X99 generation of CPUs will slow them down or disable some of their functionality???

This company has both: http://www.huananzhi.com/html/1/184/185/index.html

Is there a technical reason that combining DDR3 memory with the X99 generation of CPUs will slow them down or disable some of their functionality???

you need to use specific CPUs that support both DDR3 and DDR4, and none of them have official intel ark pages. there appear to only be a handful of them:

E5-2678v3
E5-2696v3
E5-2629v3
E5-2649v3
E5-2669v3
E5-2672v3
E5-2673v3

if you use an "offical" chip like a retail i7 chip or other retail Xeon Chip, you will probably only be able to use the DDR4 slots, since those chips don't have DDR3 controllers. or maybe they wont work at all in this board, I'm not sure.
____________

Ok that explains the ad I saw with that list of CPUs but no explanation:
https://www.amazon.com/gp/product/B07XLH1WSF/ref=ox_sc_saved_title_3?smid=A2M1V9OGLU9XW&psc=1
This idea sounds too risky. I'm sticking with DDR4 MBs. Thx folks.

This is very strange. I didn't experienced such change in the liquidity of the Conductonaut...

I guess that tested heatsink's core is not made of pure copper, but some kind of alloy not compatible with Conductonaut.

I'm pleased to return to posting, after a forced silent period: my main computer crashed (the same computer I'm writing this from), and I had to recover it first.
Good opportunity to tell some curiosities regarding this...
It is a permanently working/crunching Ubuntu Linux + Windows 10 OS computer. I usually stop it only for some preventive maintenance from time to time.

- Symptoms: On first day I found this computer was blocked in the morning, not responding to keyboard or mouse. I restarted it, and apparently it returned to normality.
On second day, I found it had blocked again, but when I restarted it and Ubuntu was booting, a black screen with multiple errors regarding hard disk access appeared.
I did a hard stop by pressing power switch, then I checked all HDD SATA and power cables.
After rebooting, the Ubuntu HDD was not recognized, and system tried to boot from Windows 10 HDD, but It failed.
A new connections check, but in a subsequent reboot no SATA devices were recognized: nor Ubuntu HDD, nor Windows 10 HDD, nor SATA optical unit (CD/DVD writer).

- Cause: Motherboard's SATA controller section failure.

- Solution: Motherboard replacement.

Starting from a veteran system with motherboard for Socket 775 processors and DDR3 memory, replacing motherboard by a current one implies also to replace CPU and RAM.

Old system.

New motherboard installed.

Installing CPU.

Applying self-spreading thermal paste.

CPU heatsink and DDR4 memory modules installed.

Now I decided to replace the previous Pascal GTX1050Ti graphics card by a Turing GTX1650 one. This card was not recognized on old motherboard... Every cloud has a silver lining!
But I found a mechanical problem due to some chassis slot separators protruding inwards, and preventing the new card to seat properly.
I Cut them with a sharp wire cutter, as seen in red (before cutting) and green (after cutting).
Once the graphics card was properly seated , a new problem arose: again, one inopportune chassis flap was preventing the HDMI connector to enter its socket.
Cutting some space in the flap and bending it back and forth with a cable plier did the trick.

This is the inside of the "new" system, and this is the outside.. In some way, a retro look that I like.

These are this new Ubuntu OS System characteristics:

And this is the same system on its Windows 10 side:
At this point, a... let's say... new problem:
When starting Windows 10, one message was shown indicating that too many changes had been detected in computer's hardware. And thus, the old OEM Windows 10 license was no more valid on this "new" system.
I had to buy a new license to reactivate my Windows 10 copy... And now everybody are happy: Microsoft and me ;-)

A very specific problem, with a simple preventive action:

- Specific conditions: 24/7 working computer, with Linux (Ubuntu) operating system, and communications based on a WiFi network interface.
- Symptom: From time to time, WiFi connection is lost, thus preventing BOINC Manager to report completed tasks and ask for new ones.
- Specific cause: WiFi network interface entering power saving mode.
- Specific solution: Deactivate WiFi network interface power management, for it to be always active.

The way I use to achieve this:

-1) Enter a Terminal window
-2) Enter command

sudo iwconfig

wlx031415926536 IEEE 802.11 ESSID:"WLAN_PI"
Mode:Managed Frequency:2.452 GHz Access Point: A0:B1:C2:D3:E4:F5
Bit Rate=65 Mb/s Tx-Power=20 dBm
Retry short long limit:2 RTS thr:off Fragment thr:off
Encryption key:off
Power Management:on
Link Quality=59/70 Signal level=-51 dBm
Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0
Tx excessive retries:0 Invalid misc:44 Missed beacon:0

sudo gedit /etc/rc.local

iwconfig wlx031415926536 power off

#!/bin/sh -e
#
# rc.local
#
# This script is executed at the end of each multiuser runlevel.
# Make sure that the script will "exit 0" on success or any other
# value on error.
#
# In order to enable or disable this script just change the execution
# bits.
#
# By default this script does nothing.

iwconfig wlx031415926536 power off
exit 0

wlx031415926536 IEEE 802.11 ESSID:"WLAN_PI"
Mode:Managed Frequency:2.452 GHz Access Point: A0:B1:C2:D3:E4:F5
Bit Rate=39 Mb/s Tx-Power=20 dBm
Retry short long limit:2 RTS thr:off Fragment thr:off
Encryption key:off
Power Management:off
Link Quality=59/70 Signal level=-51 dBm
Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0
Tx excessive retries:6 Invalid misc:102 Missed beacon:0

Another recurrent hardware problem to be mentioned:
It may cause intermitent read/write troubles on SATA units, and even system to get randomly frozen due to this.
The reason is a progressive deformation in SATA power connectors, causing an eventually bad electrical contact and subsequent power transients on SATA unit.
It can be seen at the following image:



A good connector will show a perfect paralelism on its two longitudinal sides
A bad connector is usually widened at its central zone, causing it to look like a couple of "parenthesis symbols" ( )
Please, don't trust a connector like this if you want to avoid misterious problems...

Now, a very disturbing temperature problem, demonstrating the importance of proper refrigeration:
It was observed at this system
It was mounted in an old ultracompact minitower case, as seen at this picture.
CPU cooler was an Intel stock low profile one.
And PSU was mounted directly over it.
Room temperature: (Canary Islands summer) arround 28 ºC
At this situation, Psensor readings were as follows:
As can be seen at Psensor image
- CPU temp peaked 77 ºC
CPU maximum case temp is rated 76,3 ºC, as stated in Q9550S CPU datasheet.
- temp2 (Chipset Temp) peaked 79 ºC... Too hot for my peace-of-mind !
Intel stock CPU cooler is a passive one, irradiating CPU heat all arround, including nearby Chipset's heatsink...
- CPU cooler's fan was turning at 3355 RPM: It sounded like a drone ready to take off.

Then, I had the chance to get an scrapped extra-wide PC tower case.
And I rescued from my spares drawer an old Gigabyte G-Power II Pro CPU cooler
It is a good heat-pipe based CPU cooler. It was at drawer because... It only seats at extra-wide PC cases :-)

And now, the same system after reinstalling it in a wider, better vented case, plus new CPU cooler, reaches the following temperatures:
As can be seen at new Psensor image
- CPU temperature peaks at 50 ºC (27 ºC less than before, at the same room temperature)
- Chipset temp peaks at 63 ºC (16 ºC less than before)
- New CPU cooler's bigger fan is turning at 1675 RPM... Half the previous speed, and much quieter

Now, I can go happily to drink a fresh lemonade...
🤗️

As of this kind rod4x4's suggestion:

A Gigabyte graphics card based on a factory overclocked GTX 750 Ti GPU.
After many years of intesive processing, both of its original fans became defective.
Heading to retirement?
No, if I can evite it...

-1) Let's start by dismounting the fans frame. Now the heatsink is at sight.
-2) By any chance, I had one 60x60x25 12 VDC fan, and another 70x70x25, this last with integral speed sensor. They seem to fit the heatsink very well.
All mounting holes but one coinciding with pass-through fins. So let's arrange a cable tie for all of them (thank you, rod4x4), and a convenient screw for the exception.
-3) Ok, now all fixings are in position. Time to electrical connections for both fans.
-4) Starting by joining negative (black) and positive (red) terminals, and inserting heat-shrink sleeve to all cables.
If both fans had speed sensor terminal (usually yellow), please, don't put them together. Use only one of them and isolate apart the other.
And if different size fans, use the one of the biggest size (lower RPM) fan. Joining the speed sensor terminals from several fans, will interfere signals from each other.
-5) Now we have soldered every terminals with the respective ones in card's fan connector.
Previously, I've pulled backwards along the cables the heat-shrink sleeves. If not, they will shrink with heat coming from soldering.
And if you forgot to insert previously the sleeves... now it is too late (you'll remember this when it happen:-)
-6) This is the final look after shrinking the isolating sleeves with the heat of a gas burner.
-7) And finally, we will arrange conveniently all cables and connect to fan's socket.

Now we can compare this graphics card

Before and After

To test and take profit of this rescued card, I assembled this system.

That's this:

And it seems to be working fine, as can be seen at Psensor readings and finished tasks.
👍️