MacBook Air 820-3437-B Power Cycles

[Flippers McCoy]

Hello, everyone!

I've got a MacBook Air 820-3437-B that's now power cycling. A customer brought it in with some light liquid damage to U7501, U1900, and R0960. I cleaned up all the damage and it seemed to clean up fine, I examined the affected areas with a microscope and it seemed fine. Before cleaning, it would show no signs of life upon turning it on, however the charger light would turn from green to orange. After cleaning, it just power cycles.
I tested U7501 and it's working properly (it is outputting both PP3V3_S5 and PP5V_S4), and U1900 is working properly (it is outputting PPVRTC_G3H).
I also ran it through an ultrasonic cleaner after cleaning it up manually and that had no effect.

Any advice on where to go from here?
Thanks!

[Flippers McCoy]

Re: MacBook Air 820-3437-B Power Cycles

Clarification: By power cycling, I mean approximately two seconds after I plug in the adapter, the fan spins for four seconds, then turns off for four seconds, then comes back on for four seconds and so on and so forth until I disconnect the adapter.
On a hunch I checked the current sense U7100 and they're good.

Also, here are schematics & boardview just in case anybody needs them

[Flippers McCoy]

Re: MacBook Air 820-3437-B Power Cycles

Bump!

[Flippers McCoy]

Re: MacBook Air 820-3437-B Power Cycles

Bumperooni

[Flippers McCoy]

Re: MacBook Air 820-3437-B Power Cycles

Bump

[Flippers McCoy]

Re: MacBook Air 820-3437-B Power Cycles

Final bump

[piernov]

Re: MacBook Air 820-3437-B Power Cycles

No idea but there may be 3 or 4 reboot like that in a row while the system is doing its RTC reset. No more than that.
Did you try an SMC/PRAM reset?

EDIT: oh, and try to replace U1900 with its crystal, a fucked up clock generator may show some strange behaviour

[SMDFlea]

Re: MacBook Air 820-3437-B Power Cycles

Check the JTAG connector and surrounding area .

[Flippers McCoy]

Re: MacBook Air 820-3437-B Power Cycles

I'm unable to run a PRAM reset because the computer never gets to that point, I would only be able to run an SMC reset.
I'll see about trying out replacing that clock generator and checking on the JTAG connector
Thanks for the advice!

[Flippers McCoy]

Re: MacBook Air 820-3437-B Power Cycles

Update: It magically started working again, I didn't even do anything. I suspect it may have had something to do with the SMC, as it had been sitting for a little while when I picked it up again