820-4924 no chime

[ligym60]

Hi I wanna start by saying this board was heavily damaged. when i got it it was completely dead. What's been replaced so far that had corrosion. u1900, u8030, u7400, q7320, q7321, q7310, q7311 and a few capacitors around u7400. I get backlight but the screen it came in with is cracked and the HDMI port doesn't work the area around u9750 had corrosion as well. I will order u9750 when and if I get a chime.

I'm not running it long because i believe the u5870 chip might not be working as the fans haven't spun even after waiting 60-90 seconds. I have 2 working 820-4924 that take a while for the fan to spin. but im uneasy about this chip I would say I turn it on just long enough for the screen to energize. maybe less than a minute or two

PPBUS_G3H - 12.59v
PP3V42_G3H - 3.42v
PPVRTC_G3H - 3.3v
PP5V_S5 - 5v
PP5V_S3 - 5v
PP5V_S0 - 5v
PP3V3_S5 - 3.31v
PP3V3_S0 - 3.3v
PPDDR_S3_REG - 1.65v
PPVCC_S0_CPU - 1.78v
ALL_SYS_PWRGD 3.3V
CPUVR_PGOOD_R 1.78V

Things I have tried:

1) Connect a mouse and it does flash and then its solid.

2) I can see that the screen starts out dim then gets brighter as if it was booting but I'm not sure because its cracked badly

3) I also believe the keyboard to be defective as i tried on a working board and it wouldn't boot with the keyboard in question.

[piernov]

Re: 820-4924 no chime

It's not clear what the problem is here.

[ligym60]

Re: 820-4924 no chime

First I’d like to make sure I indeed do have cpu fan activity. It’s unclear to me at this point if it is.
I just verified that It does boot
Second would be chime which also could be just audio circuit as it was also water damaged

My last question is this on I have a weird spike on pp3v3S5_LL I have a weird overshot when testing with oscilloscope I have a weird spike. Like a mosfet q7560 issue I’ve checked the snuber circuit and it seems good. I don’t want it to kill it in the future. But I’d like to ask your opinion @piernov

[ligym60]

Re: 820-4924 no chime

I just wanna fix the fan and audio circuit as it was also water damaged

My last question is on pp3v3S5_LL I have a weird overshot when testing with oscilloscope I Like a mosfet q7560 issue I've checked the snuber circuit and it seems fine. Should I replace the controller and mosfets? I don't want it to kill it in the future. But I'd like to ask your opinion @piernov

[piernov]

Re: 820-4924 no chime

Fan won't turn on until CPU gets burning hot (above 80°C or something like that).

Backlight is present so most likely the machine is POSTing properly.

Chime can be restored with PRAM reset if there's no EFI password. If you confirm you don't have any audio under macOS even after unmuting then you could suspect an issue with the audio circuit and you have to check if macOS detects an audio output.

P3V3S5_LL is switching at high frequency since it's the unfiltered output of the buck converter before the inductor, so that doesn't matter.