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820-4924 boots in SMC Bypass mode, restarts with high fans

G

grmacs

Member
It seemed like everything was working ok with this board but after it was powered off, it wouldn't power back on except with SMC Bypass. Restarting equals high fans and keyboard backlight is off. Occasionally I could get it to start normal but not shut down and power back up afterward. If I shut down, the power button won't turn it back on. Can still do SMC Reset so power button is still working when it won't turn on. Plugging in without holding power button down acts like it is in SMC bypass as well. I tested holding down shift, control, option keys to see if light would change without power button but no, so it doesn't appear the power button is stuck on.

Tried reflowing then replacing SMC. Same symptoms.
 
2informaticos

2informaticos

Administrator
Staff member
Start in diagbistic mode.
If possible to get into macOS, run HWMonitor and look for strange values.

Check resistance between pins 17/18 and 27/28 of U7100.
Also check SMC_DCIN/PBUS_VSENSE.
 
2informaticos

2informaticos

Administrator
Staff member
"SMC DCIN VSENSE is 2.2V"
Original Magsafe 2 charger?
There should be higher value.

Try the board alone whithout trackpad connected; it should start automatically, when charger is plugged in.
 
G

grmacs

Member
Ended up replacing the trackpad cable which resolved the power button not working at times. Replacing the SMC AGAIN oy fixed the high fan problem. As always... thanks for your help! pointing me toward the diagnostic and asking about the trackpad cable sent me down a road I wouldn't have guessed. I believe the trackpad cable was originally the only problem but having replaced the SMC I caused another either with a bad SMC or bad replacement job. *sigh*
 
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