820-02098 stuck on 5V

[bjf]

This had liquid-damage. After cleaning it, it worked fine but the front left USB was stuck at 5V. The computer worked fine for about a year and now all the USB ports are stuck at 5V. I'm posting pre-cleaning pictures. Any thoughts?

PP3V8_AON is at 0V
PP3V8_AON diode is at 0.180
PPBUS_AON is normal at 12.3V

 

[2informaticos]

Compare diode mode reading at 3V8_AON with good board.
I think should be higher...

 

[bjf]

Hi, yes, it's supposed to be around .360. I'm trying to find the source of the short but can't figure it out.

 

[bjf]

Any thoughts on how I might find this short? I don't think injecting voltage is going to help being that it's not much of a short.

 

[2informaticos]

A performant IR camera can detect small temperature differences; cause the injected current will not overheat anything directly.

 

[bjf]

Any other way to go about this? I'm not board repair anymore, so I'm trying to avoid investing in equipment for just one computer. Are there any likely culprits with this type of thing, maybe based on the location of the spill also?

 

[bjf]

any thoughts? any ideas besides injecting current.

 

[2informaticos]

I recently had somehow a similar problem and I found bad UT620, UF015, UF115, UG015.
Remove them one by one and check diode mode each time.
BTW, let time the board to cold down; hot board will show lower values.

 

[bjf]

Thanks. I found a dead short on P3V8AON_PVCC. Need to figure out what's causing that.

 

[bjf]

Or maybe it's in some sort of switched state and the short is normal?

 

[bjf]

Shorted C5701. Board works now. PP3V8_AON diode is still at 0.180. Weird. Should be at 0.360.