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820-2850-A GPU Panics

C

CRC2018

Member
So i've received an 820-2850-A in today with what the customer tells me was kernel panics related to GPU.
Knowing this is usually a C9560 issue I have dutifully removed C9560 and replaced it with the bigger 330uf tantalum capacitor as I normally do for these jobs. Now upon testing the board powers up but then shuts off again after around 5-10 seconds. Have tried a different capacitor and even replaced the old one to see if any difference but nothing. Getting 1.3v on pin 1 of C9560 whilst the fan is spinning.

Any suggestion on what could be wrong?

I've tried to remove the ram and the system does beep to indicate the ram isn't present!
 
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2informaticos

2informaticos

Administrator
Staff member
Did you use hot air to change C9560?
Applying heat there is not a good idea.
The cap can be easy changed just with good soldering iron.

Still turns off without RAM?
See what happens in SMC bypass mode.
 
C

CRC2018

Member
Didn't use hot air no just the iron (Ersa I-con 1 Set to 400C), stays on without the RAM and just beeps then fans ramp up to full speed. Will try SMC bypass mode tomorrow.
Also the voltage on C9560 is 1.35v steady not 1.3v as I wrote earlier which from experience is normal.

I'm wondering if it's worth popping the coil off and wiring my PSU directly to the power rail for this and setting it to run at 1.8v and see if it starts then and I get a picture or not any thoughts? I did try and inject some power into pin 1 of C9560 earlier at 1.2v and I did get a 0.3a current draw - would that be normal on this board? I don't have another to experiment with at present!
 
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C

CRC2018

Member
Can confirm doesn't start in SMC bypass mode either - fans go to full for around 5 seconds then it shuts off the same as it does in normal mode
 
2informaticos

2informaticos

Administrator
Staff member
STOP this kind of experiments.
You have correct voltage at C9560, what is the reason to inject vgoltage there???

If board stays on without RAM, no power problem.
Your board turns off when RAM is connected, because then starts the communication between CPU and GPU.
Probably bad GPU in this case.
Some hardware mod available on Internet, to disable GPU...
 
C

CRC2018

Member
I've not done the mod on this model before do you have any link to instructions for this? I've done plenty of 820-2915 hardware mod to disable GPU before so I do understand the principle.

Would bad C9560 originally cause damage to the GPU? First time i'm seeing this problem and i've fixed plenty of these boards for this issue before!
 
C

CRC2018

Member
Thanks for that good future reference material!
Looks fairly similar to the process on the 820-2915 boards.

Although I can now mark this case as solved as it appears I was the victim of not checking the whole board very thoroughly under the microscope first. Whilst I did extensively check around C9560 incase I had damaged something during replacement it didnt occur to me to check everywhere else!

It seems the real fault was that L2550 which appears to be an S0 power supply for the PCH from looking at the schematic was ripped off this board - very unusual given the placement of L2550 and I struggle to believe it had anything to do with what I did. Having replaced it with one from a donor board the board now powers up and boots normally.

So my advice to anyone reading this in the future is to check carefully the whole board for any damaged components first!
 
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