820-00281 - PPBUS 0.77v

Hello. I got an 820-00281 that is liquid damaged and has low PPBUS voltage. Every liquid damage indicator on the board is red, but only found corrosion around the backlight circuit and left speaker circuit. Board is using 20v 0.03v when I connect to just the charger. PPBUS starts at 0v when the charger is first connected and then after maybe 30 seconds or so, it starts at about 0.2v and slowly works its way up to around 0.77v and then stays like that steady. I took some measurements and figured it was a U7000 issue so I replaced it, but still have the same issue. Took another look over the board an noticed small amount or corrosion on pin 12 of Q7040. I replaced both Q7040 and Q7030, but still same issue. PPBUS is not shorted to ground either (0.383 @ F7000 in diode mode). Not sure where to look next.

PPBUS_G3H - 0.77
PP3V3_G3H - 3.4
TBA_GATE_Q1 - 0
TBA_GATE_Q2 - 0
TBA_GATE_Q3 - 0
TBA_GATE_Q4 - 0
PPVIN_G3H_P3V3G3H - 19.8
TBA_AUX_DET - 5.07
HPWR_EN_L - 3.36
SMC_RESET_L - 3.4
TBA_VDDA - 5.07
TBA_VDDP - 5.07
PM_EN_P3V3_G3H - 5.08
PPDCIN_G3H_CHGR - 19.8
SMC_BC_ACOK - 3.4
CHGR_AMON - 0
CHGR_BMON - 0
 

2informaticos

Administrator
Staff member
Try another ISL9239.
Be sure to get good solders.
Once removed, check continuity to Q7030/40 for all traces.
Also try replacing L7030 and C7030/40.
 
Replaced the ISL again, and also replaced C7030/40 and L7030 at the same time, but still have the same issue. I checked continuity to Q7030/40 with U7000 removed and did not find any broken traces. I also compared diode mode values around U7000 with another board, and did not find anything out of the ordinary. Any idea what I should check next?
 
Red probe to ground:
F7000 - 0.408

Black probe to ground:
F7000 - starts at like 0.600 and quickly goes up until the meter reads OL.
 
Diode mode is 0.389 for both the SCL and SDA lines. Both lines have 3.27v, but they both pulse down to 2.7v over and over again. Maybe bad SMC or PMIC?
 

2informaticos

Administrator
Staff member
Looks like I2C bus works, if you get pulse there.
An o-scope can confirm better.

I recommend you to get U7000 chip from scrap board, or new one from another batch.
 
I have tried 3 ISL chips already. One brand new, one from a broken donor board, and one from a donor with dead CPU, but working PPBUS circuit. All of them give me .7v PPBUS with the charger. I put the board in another top case with a battery and with battery connected, I get 11.3v on PPBUS and the board turns on, and shows low battery symbol on the screen.
 
With a fully charged battery connected, the board boots and works fine. If I connect a charger to it though, it says its charging, but the meter says 20v 0.02a so its not charging the battery. Board will not turn on with only charger connected.
 
I just tried replacing U7000, Q7030, Q7040 and all the resistors and capacitors around U7000 and PPBUS is still .7v with the charger. I have no idea what to try next, but this board is really getting on my nerves.
 

2informaticos

Administrator
Staff member
As the board works with battery alone, the problem must be on the input side.
Replace all small resistors and caps around U7000.
 
Well I replaced everything around U7000 and U7000 itself again, and still have the same issue. I tested continuity to all of the pads of U7000 when I had it removed and did not find any broken traces. Can't find any broken traces between U7000 and Q7030/40. Out of desperation I changed the SMC also, but still same issue. I have no idea what could be wrong with this one, and its driving me nuts.
 
When connected to a battery and a charger, the amp meter always stays at 20ma, even when the board is fully on a booted into MacOS. The battery Icon in MacOS shows this battery is at 100%, but it says its not charging in system info. I checked in HWmonitor and that shows the battery percentage as 98%. I left it running for about 20 minutes and macOS still shows the battery at 100% but HWmonitor now says 91%. So it is not correctly showing me how many amps the board is using and also always thinks the battery is fully charged, even when its not. Should I be looking for issues on PPDCIN_G3H?
 
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