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820-01041 fans spin no display, no chime, no lights, Short on PPVCORE_S0_GPU

N

n3vr

New member
OK so I have some knowledge of electronics but not with schematics and this level of components. I am trying to power PPVCORE_S0_GPU with my bench supply but not sure how to find the start of that circuit. I have the schematic and board view open but finding the start of each rail after 12v is beyond me.

I won't ask for anyone to hold my hand but banging my head on the desk at this point isn't working out well. Where do I start and should I even be trying to power this rail to start or do something else. I am getting shorts on 20 or so components and all are related to PPVCORE_S0_GPU when I check them in board view. I am also getting 0.8v on this rail when I believe I should be getting around 1.1-1.2 if I am not mistaken.

Thanks.

Edit: PPVCORE_S0_GFX_PH1 also shorted which I am assuming comes before SO_GPU.

Edit2: Ok I'm stupid CPU rail also has a short. I am working backwards here when I think I need to work forwards. Not sure where the hell to look to find trace down where it all begins.
 
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2informaticos

2informaticos

Administrator
Staff member
First of all, welcome to the forum.

Wht didn't post the exact ohm value for these "shorts".
Do not assume so fast a short; CPU/GPU power rails have very low values as normal.
 
N

n3vr

New member
Short to GND is around 1ohm on these 4 or 5 caps near the GPU and goes up from there as I move outward. Ranging from 4ohms up to 50.

Thanks for your time.

Edit: they're actually showing 0.8 but my probes read 0.4 so I suppose its closer to that actually.
 
2informaticos

2informaticos

Administrator
Staff member
"1ohm on a cap?"
Why not, if that cap is on CPU/GPU VCORE???
i7 and newer CPUs have very low values...
 
N

n3vr

New member
OK so should I start with DFU you think then. I don't own another mac so I would need to procure one. I don't see any other signs of faults and all rails are present. Fans spin etc. No lights however.
 
N

n3vr

New member
OK so I finally did DFU restore and afterwards I still got no display but just to see I tried to blindly boot it into target disk and it showed up on my host machine. So I then got a USB C hub and it shows video on external display. So I am unsure where to go from here as I don't have a display to test it with and not sure if I could even find one. And I don't want to order one and send it back because...ya know that's kinda shitty.
 
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