00281 with extremely hot mosfets

[captainmac]

hi, i got this thing back to life by replacing the ISL. Everything checks out, ut upon handling the board i noticed that both QB300 and QB400 get extremely hot (burnt my finger on them). when using the corresponding USBC ports.
I know mosfets can get pretty hot in general, but this is extreme. Could this point to anything? Or should i just go ahead and replace them?
The fets on the other end of the board dont get anywhere near this hot when usbc charger is connected on that end.

 

[2informaticos]

Compare diode mode readings on test points of corresponding MOSFETs.
Maybe one section is not enabled and internal diode gets really hot in such case...

 

[captainmac]

sorry was in a rush and just replaced them, mosfets are now running at normal temps.
The Mac now boots into the critical update.. before this everything was booting just normally...pfffft

 

[2informaticos]

Disconnect internal LCD and test with external monitor.

 

[captainmac]

No difference with an external screen, but now it decided to boot to a question mark folder, so the SSD is not seen.. fucking hell, the NANDS are getting all their voltages (3v3, 1v8 1v2 and SSD_CORE 1v0 ) and are getting pretty warm.. what a trolling board.
Gonna check some more and see what the hell is going on.

 

[2informaticos]

Which is the history fault on this board?

 

[captainmac]

sorry, should have added that info.

it had liquid damage.
Found some damage to U7000 area, replaced U7000 and this brought back the enable for pp3v3_g3h which was missing.
after that ppbus and 3v3_g3h came up, but board wasnt booting.
Then found corrosion under the 1v8 pad of C8028, which was disconnected from the 1v8 rail.
Ran a jumper to the cap and the board fully worked after that. (it booted into my testdrive and i could see the onboard SSD and browse its files)

i then noticed the burning hot mosfets UB300/400 and decided to replace them.
Afterwards, the board still booted, but this time coming up with the Critical Update thing.
After a couple of tries, the board can't see its own SSD anymore

 

[2informaticos]

You probably have corrosion on the SSD area too.
Clean Lifeboat connector and be sure to get all SSD voltages.

 

[captainmac]

Geez, so it decided yesterday to not boot up at all, it would draw 20v at 1,5amps, but then cut out.
I put my finger on the cpu and in the few seconds that it was drawing 1,5amps, the CPU got scorching hot... this is probably a fucked CPU...