Liquid damaged 820-00165A starts only when heated up.

[Sergioz]



Hi everyone.
I have the board 820-00165A which starts only heated up.
 Replaced components due to slight liquid damage are:
 C7797, U7501, U7600, U6101, R7641, U6100, R6130, R6132, R1440, R1445, R1344. Cleaned in Ultrasonic cleaner.
Now, the weird thing, it was going for quite some time, then after a couple of weeks it died. U6100 and U6101 were replaced when I tried to heat up the area and it booted again. Had one leg under U6101 dried, but there were no visible corrosion on the outside!
After that I dig up further and discovered that once the board is heated between the CPU and the U6100 from the side where the U6100 is located, and while it maintains around 40-50°C it goes OK. When it completely cools down it doesn't start
Any ideas where should I look further? What to measure? I feel like there's one little thing like a cap that's failing. But which one would be working after being heated a bit and in that range of temperatures? Could it be the CPU balls near R1344? Any suggestions are appreciated!
Thanks in advance.

[caspian]

Re: Liquid damaged 820-00165A starts only when heated up.

A photo of the suspected mainboard area would be helpful to decide. I mean the area between the CPU and the U6100 where you heated.
Since you said the components near the CPU got corroded, it is probable that the CPU balls got corroded too.

[Sergioz]

Re: Liquid damaged 820-00165A starts only when heated up.

Attached the photo of the region where the heating worked better. IMHO as it is now the board looks clean. All the residue on the photo is the flux cleaner stains, not liquid. Now it gets interesting. I replaced the EFI chip again with the brand new one. I do this a few times per day, so not a big deal to reprogram it with the new clean EFI with clean ME region. I have three absolutely identical boards with different type of damage, so I tested this EFI dump on others two and it works perfectly well. All three boards have serials with FVFT.....H3QF so again, these are absolutely identical machines. After replacing the EFI and programming it with tested dump, the board in question starts and keeps running. But with no chime, no screen, USB works, SMC reset works, and the fan keeps spinning but no boot. So, IMHO the problem is with EFI, or traces to it. The CPU was clean, the corrosion was on the opposite side of the board, where the BIOS chip is located. Any ideas? Thanks.

[caspian]

Re: Liquid damaged 820-00165A starts only when heated up.

since you said the other side of the board was liquid damaged, this photo does not show any clue. So more tests should be done on this laptop to discover more clues of the problem. Testing laptops sometimes takes more time and effort. that is why laptop repair is considered as a part-time second job with no delay guarantee.