HOW BAD IS MY PCB DAMAGE A2338 820-02337 water damage burnt caps

[TheNuclearOption]

Short on ppbus. Taking 3a at 1v and nothing is heating up. I have at least 3 pads that are badly burnt from capacitors. Ive scraped (at least attempted to) not sure how good I did? Are these possibly containing internal shorts? Do you think they need to be scraped more?

[mon2]

Check their resistance to ground. You may be shorting to the next layer(S) of this multilayer pcb. No power during these tests.

[TheNuclearOption]

Check their resistance to ground. You may be shorting to the next layer(S) of this multilayer pcb. No power during these tests.

Thanks for the replay.

They all measure at 0.5 ohms (a dead short I think)

What else can be done if they are shorting to the next layers? Cut them out?

These are all part of the left speaker channel.

[TheNuclearOption]

There was an internal short. I was able to carve it out. Ppbus is no longer shorted to ground but it is measuring at 21 ohms. I'm getting 12.4 volts at ppbus when plugged in. Is a partial short. Likely still? It's drawing 0.01 amps now on ppbus

[mon2]

Measuring 12v4 on PPBUS is a good start but the resistance @ 21 ohms does not make sense. Remove all power. Meter in the lowest scale. Then measure the resistance to ground again here. You can also post a picture of your meter face so we can confirm the units of measure of this rail. Perhaps it is 21 kohms here?

[TheNuclearOption]

My mistake, I'm getting 12.24v to ppvbatt and 21ohms I think to ppbus.

I removed my fuse, it's blown

[mon2]

To confirm, you have removed the blown use?

the downstream side of the removed fuse is showing ~21 ohms to ground?

[TheNuclearOption]

Yes I removed the blown fuse. I'm not sure what side's the downstream side but ppvbatt (bottom pad on the motherboard in the photo) is one side of the fuse ppbuss(top pass on the photo) is the other. Ppbuss was showing a short to ground previously until I carved out the internal short. Now it's showing 21 ohms I think. I'm not sure if that photo comes across

[TheNuclearOption]

Did I get that reading right? Does that mean there's most likely a partial short still?

[mon2]

A2338 820-02337

- having a hard time locating this logic board schematic. Did you mean 820-02773 ?

Update: Confirmed that the BV file matches if 820-02773. The pad you are showing in the pic is the downstream side of PPBUS_AON.

[TheNuclearOption]

Okay thank you. Is that too little ohms for the downside stream of ppbus_aon?

[mon2]

Yes, the resistance is too low for a normal rail. Remove all power, meter in the lowest scale on your meter (200 ohm is ok) -> apply one meter probe (either color is ok) on this same downstream PCB pad; other meter probe onto any inductor on the board. What you are hunting for is if a high side mosfet is defective and causing a leak onto another power rail.

That is, this high voltage rail of PPBUS_AON is used as a buck convertor by other power rails. This is where a high voltage input is used to create a lower voltage rail by other circuits on the same board.

The key concern is that a high side and a low side mosfet will toggle on / off to dial up the desired lower voltage rail. If the high side mosfet is defective then that low voltage rail has been spiked by the high input voltage and this board will then most likely be a no-fix case. To be determined.

Probe away and report anywhere you see a low resistance between this pad and the inductor. Then that inductor needs to be reviewed as to which power rail is impacted by this hit.

[TheNuclearOption]

I'm getting 23.7 ohms on the 3 inductors (L5840, L5820, L5800) on the pp3v3 rail and 21 ohms on the inductor (LF800) on the pp5v rail (same resistance as the downstream ppbus)

[mon2]

Measure the resistance from the PPBUS_AON pad of the removed fuse to L5840. One meter probe on PPBUS_AON and other probe on L5840. What is the resistance?

Repeat for PPBUS_AON and LF800 inductor. What is the resistance?

[TheNuclearOption]

about 17 ohms on L5840 and and 14.5 ohms on LF800. That seems very weird to me since I just measured them and got the resistance I mentioned last post.

[TheNuclearOption]

I measure again, and now im getting around 4 ohms. seems to keep dropping. Im gunna look at the internal short again

edit: I injected 1v into ppusb_aon and it's still only drawing 0.05a

[TheNuclearOption]

I measured again today, 19ohms and 16ohms. Is there a chance there is something wrong with my multimeter? Could it be a partial short moving around slightly?

[TheNuclearOption]

I'm not sure where to go from here?