A1990 820-01041-07 no power

[hgoncalves]

Hi.

I have an A1990 820-01041-07 with no power.

The mac had contact with a bit of water, and U9080 area was a bit oxidated, and the area near UB300 also seamed to be a bit oxidated (very few signs), but because it has 20V I didn't replaced it.

I've replaced RB258 because it was a bit oxidated, and U9080 because that area also had a bit of signs of oxidation.

I have 20V on ampmeter, and the ampeter progressive reaches 0.255A and then it reboots.

I can't see anything else damaged, and couldn't find anything shorted.

Do you have any idea to where I should focus?

Can you help?

 

[2informaticos]

"U9080 area was a bit oxidated"
Very likely dead NANDs...

 

[hgoncalves]

Hi.

I can't se nothing shorted on the NANDs

Can you please help diagnose a dead NAND?

UB300 also had a litlle sign of liquid, but his LDOs and CC1/2 diode readings are ok. . Can it be UB300?

 

[2informaticos]

Not only short means bad.
Corrosion arround U9080 caused overvoltage to NANDs for sure.

 

[hgoncalves]

Hi.

The corrosion was very, very small. only around R9080/83.

I just notice that PPBUS_G3H_SSD0_SNSoscilates between 12.220V and 12.60V. Shouldn't be 12.60V steady? Can it be it?

 

[hgoncalves]

Hi,

Is there any way for me to be sure that it is a NAND problem, so I can propose to the client to replace all NANDs?

 

[2informaticos]

Bueno, this is not an exact science...

 

[hgoncalves]

Hi.

Can the NAND's be taken out of other A1990, or they need to be programed before soldering on the Mac?

 

[2informaticos]

You can take them from similar board, maintaining the position.

 

[hgoncalves]

I only have an A1990 820-01814-A board.

Can I use those NANDs?

 

[2informaticos]

Yes, should work; if you respect basic rules.

 

[hgoncalves]

Hi,

I've replaced all NANDs, but I still have the same result.

Any other idea?

 

[2informaticos]

All USB-C ports switch to 20V?
Did DFU restore after changing NANDs?
BTW, did you change all NANDs, both sides?

 

[hgoncalves]

Hi.

Yes, all USB-C ports switch to 20V. However the Mac seams to be rebooting after a few seconds, but maintaining 20V.

Yes, I've done the DFU restore, however it fails because the reboot I suppose (the error was give up waiting for the device).

Yes, I've changed all 4 NANDs (2 per side).

 

[2informaticos]

Good trackpad and battery connected when tried DFU?

 

[hgoncalves]

Hi.

Yes, just tried with a kown good TP and battery, but still the same

 

[2informaticos]

Erase U4770 and try again DFU restore.
Make backup first...

 

[hgoncalves]

Hi.

Erasing U4770 didn't solved the problem.

I still get the DFU error (ing attached)

 

[2informaticos]

DFU Mode Restore (Macs) - LogiWiki

We have Apple MacBook and iPhone Diode readings and general fault finding information compiled by the leaders in this area

logi.wiki

 

[hgoncalves]

HI.

Is it a good idea to reball T2?