820-2915 Only posts with battery and no HDD

[Ryanlen2]

I have a 820-2915 that will only boot/post on battery power. No liquid damage. When adapter is used without battery the fans spin up for a few seconds then shuts down and restarts (All S3 rails cycle.) Also, will not stay powered on with HDD plugged in. (boots, HDD spins for a couple seconds then shuts down.)

PP3V42 - 3.42V
PPBUS (Battery only/ not turned on) - 12.8V
PPBUS (Battery only/ turned on) - 11.62V
PPBUS (Adapter only) - 12.56V
PPBUS Diode - .425

PPDCIN - 11.80V
PPDCIN (Turned on) - Starts at 11.80 and drains to 11.16V)
PPDCIN DIODE - .622

Genuine 85W charger.

Thanks have a good day.

 

[dukefawks]

on battery it shuts down with HDD plugged in or only on AC? Check resistance between pins 17/18, 27/28 of U7000?

 

[Ryanlen2]

Yes. On battery it shuts down with HDD plugged in after post/chime. On AC, the board cycles and restarts. The fans spin up, then down. Does not post.

Resistance on 27/28 - 20.6ohm
Resistance on 17/18 - 3.2ohm

On AC I have 12.54V when fans are spinning. 12.56V when they stop.

Thanks.

 

[dukefawks]

I have no idea....Maybe an issue in the 5V rail so TPS51980 and the FETs. It could be anything really, even the GPU.....

 

[Ryanlen2]

Ok Duke. Fair enough. I would like to try to get it to run on AC power as it does DC power. Why would it power up to blinking folder on battery and not AC? The hard drive thing seems like it could be a separate issue but maybe also related. IDK. Where should I start to try to narrow it down? I have checked U7201. PM_SLP_s4_l drops when the fans do on AC power. All s3 rails drop. I have S5 rails steady. I just need a little direction. Thanks man.

 

[dukefawks]

Again I have no idea. On AC there could be some ripple introduced that messes with a power rail. I have no direction to offer here but to heat the GPU. If this is an Apple refurb board with no serial sticker on the RAM slot then you can toss it in the trash right away.

 

[Ryanlen2]

okay. Thanks anyway. Have a good Day.