820-3787 no display on internal or external

[arghhh]

I was using a working 3787 to compare measurements around L7130/L7520 when my probes slipped and shorted some things together (not sure what). The computer immediately shut down, and now when I boot it there is no display on the internal LCD as well as over HDMI with and without the LCD unplugged. It does seem to boot because it chimes and the volume keys work, and it responds to the ALS. I tried PRAM and SMC reset, nothing.

Is there any hope or is the GPU dead?

 

[dukefawks]

More likely something in the MUXing circuit, voltage spike on 3V to one of the MUXes. This is going to suck.

Enable remote desktop on the OS and log into the machine to see if the GPU is recognized.

 

[arghhh]

How do you suggest I enable remote desktop? Boot the SSD in a working machine?

I'm getting 0v on C8760 also.

 

[dukefawks]

That is controlled by U9600 MUX. This whole circuit of MUXes is so complex, I don't even know exactly how it works. GPU getting core power?

 

[arghhh]

No, 0v on C9363. 15 ohms to ground.

 

[dukefawks]

Again the enable comes from U9600. Any of the 5 rails that U9600 controls coming on? May only pulse once, as U9600 might shut everything down when the PGOOD signals are not coming high, but not sure about that.

 

[arghhh]

No, I don't think any of them are coming up. PP3V3_S0GPU_MISC has ~0.38v on it if that means anything.

 

[arghhh]

Is there any chance this is BIOS?

 

[dukefawks]

I'd like to hear your logic behind that besides it being easy........

 

[arghhh]

It's the only thing in the area that could have been shorted with the probes?

 

[dukefawks]

I'll give that a 1% chance. More likely there was a voltage spike on 3 or 5V bus.

 

[arghhh]

So I checked in system profiler and it doesn't see any GPU, only Intel Iris. Should I replace U9600 or fucked?

 

[arghhh]

I haven't checked yet if U9600 is getting 3.3v on R9600 R9601 but I would assume so at this point. The only other thing I'm thinking it could possibly be is that somehow the backlight IC got fucked since it is in the area I was working in and is sending the wrong signal on the I2C bus to the U9600 mux and shutting it down. Would that make sense?

 

[dukefawks]

I doubt the BKL chip would cause this but you can pull R7781/82, should work without. Of course the GPU is not recognized, it is not getting power. Check power to U9600

 

[arghhh]

I have 3v on R9600/R9601.

 

[dukefawks]

Watch Louis's latest video please.