820-4924 Turns on once, then cycles

bjf

Member
This liquid-damaged board will turn on once but then once you try to turn it on again it just cycles, with the CPU getting voltage during that cycling. If you let it sit for a while, it will turn on again, and then not turn on after you shut it down. Any idea what could cause something like this? I attached pre-ultrasonic cleaning pictures.
 

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2informaticos

Administrator
Staff member
Does it boot in SMC bypass?
Be sure to rebuild any corroded trace, if is the case.
Also some resistors could be damaged.

Check how ALL_SYS_PWRGD and pins 7 & 3 of U1950 react.
Check all SPI Bus Termination resistors and traces/solders for U6100.
 
Last edited:

JohnB8812

New member
Have you tried it without the battery plugged in? Could be a battery issue too. Other than that, check what 2informaticos said
 

bjf

Member
ALL_SYS_PWRGD and pin 7 both cycle. Pin 3 stays at 0V. Keyboard connector needs work so I can't do SMC bypass right now. I'm still just trying to get it to turn on consistently so I haven't tried to connect a battery yet. I did notice though that the SDA and SCL battery lines were not measuring correctly (there was a big difference in diode mode) so I replaced U7100. It didn't change anything but the lines are measuring correctly now.
 

2informaticos

Administrator
Staff member
Solder an wire on SMC_ONOFF_L (R5115/16 pads), so you don't need keyboard for SMC bypass.

No pulse at all at pin 6/U1950?
 

bjf

Member
No change after SMC bypass. No pulse on pin 6 of U1950. Everything else seems to be cycling.

This board will actually boot all the way once. And then it won't. You have to let it sit for an hour or so which makes me think there's something going on with a capacitor that needs to drain. That's all I can come up with.
 
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