820-01987 low voltage on PP3V3_G3H

Hello. I got this 820-01987 board in that was pretty badly liquid damaged. Most of the damage was around the backlight circuit and CD3217's. The board was originally stuck on 5v and PPBUS_G3H was only 0.7v and 0.068 in diode mode. I removed C6456 and the diode mode value on PPBUS went up to 0.410 and now I get 12.3v, but still 5v on amp meter. PP3V3_G3H_RTC was 0v, so I replaced U6903 and had to replace U3100 also and that got me 20v back, but no amps. Now PP3V3_G3H_RTC is 3.3v, but PP3V3_G3H is only 0.9v, but seems to have the correct diode mode value of 0.398. I found small amount of corrosion around Q7680, so I replaced that chip and U7650 at the same time, but still have only 0.9v on PP3V3_G3H. Any idea what else could be causing this or what else to check?
I have 0.9v on 3V3_G3H so it does seem to be enabled somehow. The 3V3 enable signal for U7650 is just a test point that does not go to any other chip. U7800 is powered by PP3V3_G3H_PMU_VDDMAIN, which is also 0.9v because its comes from PP3V3_G3H. So I do not have any voltages that come from U7800 since it is not turning on. DFU also is not going to work if I am missing all voltages from U7800


If you found some corrosion around Q7680, post the resistances between:
- pin 3 (high side MOSFET gate) of Q7680 and pin 24 of U7650,
- pin 5 (low side MOSFET gate) of Q7680 and pin 27 of U7650,
- any pin of L7690 inductor and pin 17 of U7650,
- any pin of L7690 inductor and pin 18 of U7650.

Please also post the resistance to ground on pin 29 of U7650 as it seems you have a non-working LDO5 output as well.


Staff member
Don't be so sure; why didn't check before?
U7800 LDO block is powered from 3V3_G3H_RTC (via R7900), which you've said is present.
T2 requires only AWAKE and SLPS2R voltages to go into DFU.
Also need SSD voltages, to complete DFU...
I checked the resistances on Q7680 and they all match vs a good board. I was not aware that the LDO block of U7800 was powered by PP3V3_G3H_RTC. So based on the voltages below, it looks like U7800 is the issue?

PP1V1_SLPS2R - 0v
PP3V3_G3H_RTC - 3.3v
PP1V8_SLPS2R - 0v
LDO_CORE - 1.476v
PP0V8_SLPS2R - 0v
PP3V_G3H_RTC - 0v
PP1V2_AWAKE - 0v
PMU_LDO3_OUT_R - 1.814v
PP3V3_AWAKE - 0v


Staff member
So U7800 is powered up (from 3V3_G3H_RTC), but fails to generate several LDO rails.
If none of them is shorted, or has low ohm resistance to ground, then change U7800.