820-3332 GPU Kernel Panic

tlough75

Member
I have on the bench an 820-3332, so it is an Early 2013 15". the first time I saw it on my bench the screen would randomly flicker and the laptop would crash. I resoldered U8900 and it seemed to fix it, but a week later it is back on my bench. According to the customer, after it is running for a while it would crash. I myself only got it to crash once with a GPU Kernel Panic error, saying something about "mux-reg 3" or something of that nature. I measured PPVCORE_S0_GFX_PH1 and it has 900mV even though the screen went black, but after the screen turned off. After few moments the whole machine would turn off. I noticed the battery has a "service me" label but I assume this is a separate issue. So far at idle, I am able to run it for the past hour without the SSD and no crashing. I don't see in "About this Mac" if this machine has a discrete GPU. Any Ideas? Or is the GPU toast?
 

tlough75

Member
I used HWMonitor and it says the SSD has 63% service life left, though I am not sure if that is helpful.
 

tlough75

Member
I actually have 3 of these machine. Early 2013 15" Retinas with the same issue. On #2 though, when screen goes black, The GPU VCORE goes to 0V so I am assuming U8900 may have broken solders.
 

tlough75

Member
I'm assuming since I still get PPVCORE_S0_GFX_PH1 & PH2 even when screen goes black that the GPU is faulty. On the second 820-3332 when the screen goes black, GPU VCORE drops to 0V, so I would think that is U8900. Am I correct in my thinking?
 

2informaticos

Administrator
Staff member
Did you resolder U8900 for the 3 machines?
If GPU VCORE goes off is not a certain sign of bad U8900.
Depends of which kind of fault develops GPU in that moment.

You can try to disable discrete GPU, as there is an easy hardware mod, already posted on the forum.
 

tlough75

Member
Machine 1: Screen goes black but GPU VCORE stays at 900mV. Shows kernel panic. NO Liquid damage or drops

Machine 2: Screen goes black and GPU VCORE goes to 0V. NO known Liquid damage or drops. No Kernel panic

Machine 3: Randomly freezes and requires a restart. No known liquid damage or drops.

Just wanted to note that they are all exhibiting different faults. NOt asking to solve all three at once :) though would be nice to get them all fixed and out of here.
 

tlough75

Member
I re-soldered U8900 and it is no longer kernel panicking or crashing. Stress tested for 2 hours and it seems to be resolved. Thank you for your help.
 
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