A1398 820-3332 tries to turn on 0A - 0.4A - 0A after previous black screen issue and shorted Q7510

[it-solve]

Hi Guys,

Have this board that has a black internal screen but used to work on the external screen. A graphic load software won't start on the external screen.
Thought it could be a U8900 cold joint issue and resoldered it, in the process resoldered U7400 as well. Afterwards, the board won't even turn on and would stay at 0.28A with and without a battery.

Found short on Q7510. Not sure if the heat somehow triggered it, went and replaced it. Now it tries to turn on and switches off with a battery, keeps repeating it - 0A - 0.44A - 0A

Measured that
SMC_PM_G2_EN - jumps 0 - 3.3V and repeats, together with P3V3/P5V_S5_EN signals.

Went through the board to hunt for shorts but couldn't locate any.
SMC_PM_G2_EN is SMC output line, how I can check if losing voltage before?

PP3V42_G3H - 3.4V

 

[2informaticos]

SMC will disable the signal, if detects a problem on the board.

External monitor is driven by discrete GPU only.
How could U8900 cause missing internal video???
You've caused more damage on the board doing something not related with your problem.
Resoldering U8900 is a must do on this board; but not generating another problem!

Touching U7400 with initial problem, was bad idea.
Some bad solder caused Q7510 fried.

Remove R7940 and test the board again.
Also try starting in SMC bypass mode.

You may need to change U7400 now.
Check all its resistors and traces to Q7510.

 

[it-solve]

Had this before with a 2013 A1398 model as described by TCRS -

. Resoldering pads resolved the problem in that case. Thought this could be the same as it wasn't showing internal video, but external seemed to be working.

Agree. I should not have touched U7400. The low resistance on its pins deceived me.

Removed R7940 and tried SMC Bypass (if this is the one) by shorting C5710, doesn't even attempt to turn on.

Resoldered U7400 a couple of times now and seem to make good contact. Traced the PHASE1/2 and UGATE2, traces seems to be fine
u7400 is listed as ISL95831 on the schematic but MAX15199 on the board. Seems I can grab ISL95831 from A1286, is that same as the MAX?

 

[2informaticos]

Compare schematics, to choose equivalent IC.
3332 uses same chip as 3115 and 3330 (MAX15119).
2915 has different layout (MAX17511).
ISL95831 is not compatible with them.

 

[it-solve]

I have replaced the U7400. No fan spin stays at 0.28A and can see the replaced Q7510 gets hot.
But have very low resistance on CPUIMVP_PHASE1/2 - 1Ohm. Is it expected?

Also seems like it blow the Q7510 again, shall i replace it one more time? I have lifted the coils around the CPU and lower side is the CPU side.



With removed Q7510 it turns on and spins the fans

 

[2informaticos]

CPU may have very low resistance to ground as normal; just compare with other similar board.

However, burning Q7510 probably fried the CPU.