Macbook Pro Retina A1398 PPVCORE_GPU

Kittu

Member
Hi:
Im having an issue with a A820-3332 motherboard with PPBUS_G3H at 2.8V instead of 12.6V No chime, no fan spin one wire-circuit working with green light on MagSafe.
On scouting, I find this may be perhaps because of PPV removing U8900 (62882), the PPVCORE_GPU shows 18 ohms to ground!

Please advise where to start...
 

2informaticos

Administrator
Staff member
Did you power up the board in such condition???
You've left Q8930 with Gate pins floating on air.
GPU could be fried now, if you did that.

18 ohms looks good there.
Change Q8930 and pray...
 

Kittu

Member
Aaaah! My Bad. Though I just checked, removing Fuse 7040 and 7041 shows 12.5V on pins 1 of the fuses. meaning something after the fuses is pulling PPBUS_G3H town to 2.5V. Hope this didn't fry the Q8930!
 

Kittu

Member
Removed Q8930. Fan spin and system chimes - though the original issue of eDP remains

to give a background, I had to remove the U8900 as pin 39 was perhaps shorted to pin 40 though the embedded LCD worked. After replacing U8900 the display disappeared. I again removed it.
then suddenly the issue you highlighted of Q8930 shorting happened. Now, is there a way of ascertaining if 62882 is working properly and whats the probability of my GPU having fried....

Kindly advise on checking 62882 and probability of GPU dying with your experience.
 

2informaticos

Administrator
Staff member
Did you finally power up the board without U8900, despite of my advice???

If GPU coils show 18 ohms, you can still have a chance.
May need to change Q8930 and U8900 at same time.
 

Kittu

Member
Alas it was powered up before I posted when the Q8930 was shorted....
18Ohm was Fuse F7040/41 to ground PRIOR to removal of the Q8930.
Have ordered the Q8930 at Mauser so will take a few days.

At the moment after removing Q8930 and replacing the 62882 I did power up with GPU and CPU both warming up. Fan n Chime OK.

"If GPU coils show 18 ohms, you can still have a chance" Please give me parameter and location to measure.
 

Kittu

Member
Please advise if I also need to replace Q8961/31 649135PBF along with the Q8930. If so, as the 649135PBF is getting hard to find, a reference source will be highly appreciated.
 

2informaticos

Administrator
Staff member
In THEORY, you should change Q8931/61 and U8900 too.
Usually not needed, but you should know how to properly check that area, to ensure none of them is bad.
You can change them with MOSFETs from other (high current) CPU/GPU power supply.
But do NOT mix high/low-side MOSFETs; low-side MOSFETs require embedded Schottky diode!
 

Kittu

Member
Is there a way to check if the Q8931/61 are good by on-board diode mode voltage or normal resistance checks?
kindly advise on this as finding replacement equivalents introduces another variable in the equation of an already complicated scenario of GPU/Q8930/62882
 

2informaticos

Administrator
Staff member
If 18 ohms at GPU coils, probably low-side MOSFETs are good.
But you can remove them and measure out of board...
 

Kittu

Member
As stated, fans spinned, system chimed with Q8930 removed. However, Replacing Q8930 as well as 62882 and powering the board with MagSafe results in F7040/41 voltage dropping to 3.2V (resultantly no fan spin/ chime anymore) with coil showing a PPVCORE_GPU voltage of 0.97 and Q8930 heating abnormally. Removing Q8930 restores fan spin and chime.

Please advise.
 

2informaticos

Administrator
Staff member
STOP to power up a board after changing something, without checking for other problems.
If you find something burnt, think about a reason; try to eliminate the problem first.
There are some other components around U8900, Q8930; especially bootstrap R/C network.
ALWAYS check good continuity between MOSFETs Gate and controller chip.
 

Kittu

Member
R/C Components check OK around the 62882 and Q8930.
Request you to point me to the specific test points. Further, PPVCore_GPU is 0.97V when Q8930 heats up.

Is there a possibility of the GPU (despite showing 16-18 ohms at coil) being somehow internally shorting leading to a virtual overdrive of the Q8930 causing it to heat up abnormally and causing the F7040 voltage to drop to 3.2V, in which case replacing the GPU may be the only option unless suggested otherwise.
 

2informaticos

Administrator
Staff member
Very strange to get different PPBUS_G3H and GPU core voltage, if Q8930 is shorted.
Ussually same voltage should be on both rails.

Your GPU is probably dead, after such torture...
 

Kittu

Member
GPU and Q8930 replaced. Coil resistance drops to 5.6 Ohms. System boots. No excessive heating of any component but still no vcore GPU and hence no eDP image.
please advise on further diagnosis.
 

Kittu

Member
Hi! Having changed U8900 and it?s related RC components, replaces Q8930 I have PPVCore as 1.05 which drops to 0.89 on fan spin (GPU has been removed to troubleshoot for now).
HOWEVER , GPU FB Supply and GPU 1V05 Supply remain 0V on fanspin with GPU removed.

My question is, are the supply levels OK without GPU and if I need to further troubleshoot the power units before I get the GPU in place.
 
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