820-3332 - No GPU Vcore

overshoot

Member
Hi,

I have that 820-3332 with a previous repair attempt on U8900. The rest of the board looks clean, no corrosion.
U8900 area looked pretty bad so I have decided to rebuild it swapping all the nasty components.
I did also swap U8900 from a donor board.

Once powered on, I could hear something clicking. It was Q8930.
I have now removed it, checked for short and put another in place.

Board is turning on, chime, will respond to PRAM but no GPUVcore whatsoever.
I've double checked every resistor around U8900 and they all measure fine.

I am missing the enable signal on pin38 coming from the GMux chip.
So I am now confused in where to start. Should I be getting an enable signal even if U8900 is bad or not?
It's not even pulsing.
 

2informaticos

Administrator
Staff member
Check if U9100 gets all voltages first.
Next, check for corrosion on its area and reflow with quality flux (no chinese honey).
Replace GMUX if needed.

Just in case, check is something change connecting external monitor.
 

overshoot

Member
My bad... using an oscilloscope, I can very briefly see them all showing up for some milliseconds then down to 0V, so does GPUVCORE_EN.
However PPVCORE_GPU goes up to 200mV and then drops to 0V.

Resistance to ground PPVCORE_GPU is 22ohms which seems ok.

Could it still be a bad ISL area (ISL itself has been replaced 3 times) or does sound more like a GMUX issue?
 
Top