820-3024 - PPBus_G3H fluctuating. NSFW warning.

[gcain]

Board had a little corrosion; refer to attachment.
After an ultrasonic, some flux, another ultrasonic and a stint in the oven it turned on and chimed, then switched off.

Now it spins the fans for a second or two, then turns off for a second or two, then on, then off etc. Eventually it slows down to just twitching the fans every few moments.

@ J6900 DCIN fluctuates from 16.28 - 16.80.
F7030 goes from 13.9v to ~3v, then back up.

C7200::1 goes from 13.9v to about 3.6v and back again.

 

[larossmann]

Resistance between pins 17/18 of U7000, and pins 27/28 of U7000?

Is PP3V42_G3H steady?

And I bet U2700 was corroded as well.

This will likely be an issue around U7000. Battery current sensing, not charger current sensing, so my bet is on R7051/R7052/R7050 & traces between them and the U7000.

 

[gcain]

PP3v42_G3H is stable.

U7000::17/18 = OL
U7000::27/28 = 20ohms

U2700 looked okay going by the photos I took.

R7050 is measuring almost 0ohms. (Whats the correct way to measure a current sensing resistor like this?)
R7051 is 3Mohm (nothing wrong there...)
R7052 is 0.1ohm

R7051 is obviously blown, but C7050 looks pretty suspect too; will replace both and report back.

 

[gcain]

Now I get no fan spin and F7040 is going as log as 1.8v.

Clearly I am on the right track, I can see now that it's cleaner a few traces are burnt / corroded away.

Will sort them next.

 

[aprendiz]

check value of R7005, I suspect a bad ISL, what is resistance between pins 17/18 from ISL now??

 

[gcain]

R7005 measures okay.
Resistance U7000::17/18 = 2.1ohms

 

[gcain]

U7000 is getting really hot then it goes cools down for a second or two then gets hot again.

Should I replace it, or is this caused by an issue somewhere else?

 

[dukefawks]

It's probably dead.

 

[gcain]

OK will swap it out then.

I was wondering if it was trying to supply enough current to a capacitor that was shorting and giving up after a bit; then trying again.

Will swap it and report back.

 

[dr. moast]

Am I the only one wondering about why there is a NSFW warning in the title?

 

[gcain]

Am I the only one wondering about why there is a NSFW warning in the title?

Gore. Did you see the board?

Also a little bit of click bait factor.

 

[larossmann]

Look at the diagram, the only way R7051/R7052/R7021/R7022 are ever going to go bad unless they are corroded off the board is if U7000 dies and shorts to ground. Anytime those resistors are dead(and not just the traces around them) it's a surefire bet the U7000 is bad as well.

 

[gcain]

Thanks for the extra info.

I swapped U7000, turned it on and something went SNAP, but I'm not sure what or where yet. :/

Might be too much wrong with this board after all...