820-3332-A A1398 weird power problems

[2informaticos]

Beeps is not same as short.
Some power rails have low value as normal; and beeps for this reason.
If you get much higher value on identical board, this is sign of failure.
However, that cap is connected on the same power rails with many other external components; not sufficient reason to doubt about PCH (yet).
Inject voltage and check which component heats...

 

[Melvinzill]

Will do once PSU arrives. Also ordered a fresh can of freeze spray.

 

[Melvinzill]

BTW where is the best place on that line to inject voltage?

 

[2informaticos]

Pin 1 of L7260 is probably the biggest pad.
C7292/93 easy to solder too.

 

[Melvinzill]

UPDTAE:

I got my new Bench PSU and after going through a can of freeze spray with a draw of 1A I found C7293 to heat up. Removed it alongside C7292 and now it draws .001A at 1V and the diode mode on L7260 changed to .108

Any better?

 

[2informaticos]

Resolder components and check diode mode again; do NOT power yet.
If still low value, Q7260 is probably burnt.
I recommend you to directly change both U7201 and Q7260.

 

[Melvinzill]

What do you mean by low value? What is normal?

 

[Melvinzill]

With the parts back on the board its .087 on L7260 and .42 on L7220

 

[2informaticos]

".087 on L7260"
Not too low; I suppose board is not cooled yet.

Did you change mentioned components?
Check diode mode on L7030 too.

 

[Melvinzill]

Yeah, that could be as with a cold board (room temp) its now .096


I did change the caps but U7201 and Q7260 is the original replacement as I didn't have any and waiting fo china would take ages

L7030 is .486

 

[2informaticos]

You can try to power up the board now; if all components are back in place.
But I recommend you to follow exact steps mentioned bellow for "power sequence" .
Cross the fingers, pray and pray more; finally connect charger.

 

[Melvinzill]

Oof. more issues! No fan spin or anything. But then I noticed a big fat burn mark on R6920. Replaced it but now the green light comes on for about 5 seconds before turning off and with freeze spray I can see R6902 immediately heating up. Any idea?

 

[dukefawks]

Just skipped quickly through this thread, but why are you putting time and effort into a board that had 12V on the 5V rail? Not want to rain on your parade, but the chance of a dead PCH/CPU is pretty much 100% here.

R6920 getting hot will be a short on 3V42 or on the input of U6990. I'm going for 3V42 short that traces back to the PCH.

 

[Melvinzill]

Yeah. Probably financially an absolute waste of time. But I just wanna get this fixed no matter what. Yeah I?m weird.


Replaced U6990 but that helped nothing. Any way I can find out if the PCH is actually bad? I mean if I knew it was I?d replace it but I?m not sure if it is...

 

[dukefawks]

is 3V42 shorted? If yes inject 3V into that rail and see if PCH heats up. If it does then you should really stop there as there is probably even more damage beyond the PCH too.

 

[Melvinzill]

It heats up a bit, yeah... Should I order a new PCH from AliExpress or get one from a donor board and attempt a replacement? Never replaced a PCH before though I did a CPU upgrade on an 09 white MacBooms so it shouldn't be much dirfferent...

 

[2informaticos]

I bet you have more damage than PCH only...

 

[dukefawks]

0.76mm or 0.45mm balls, that is the difference. You can order it new or get it from a dead board, but you maybe it will be better to fix the dead board you are pulling it from than this thing.

Seriously, this will be a total waste of time and money, this thing is done.