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820-00165 No Power But S0 Rails Pulse

brunomotter

brunomotter

Member
Hello. Got this board here initially with no power at all. PPBUS_G3H was stuck on 1.6V. After inspection I found corrosion around C2952 area. Cleaned everything and replaced all caps that looked bad and also U8000 that was shorted to GND. Now board gets steady 8.56V on PPBUS_G3H and tries to enter S0. All S0 coils pulse including L7310/20 but after that it goes to 0V again and nothing else. Already inspected whole board for other corrosion points but could not find anything. Where should I look now?
 
2informaticos

2informaticos

Administrator
Staff member
Check all SPI Bus Series Termination resistors and their traces.
Be sure U6101 has good solders.
You may need to clean/remove J6100.

Do you get two pulses on the coils, or power cycling?
Just in case, try to start in SMC bypass mode.
 
brunomotter

brunomotter

Member
Hello. I get 2 pulses and then 0V on S0 coils. All SPI resistors read OK. Re-soldered U6101 just in case and removed J6100. When in SMC bypass I get quarter fan.
 
2informaticos

2informaticos

Administrator
Staff member
Possibly accumulated crap underneath CPU.
Heat it to 180-200 degrees, no more than 15-20s.

May need to reball SMC also.
 
Last edited:
brunomotter

brunomotter

Member
I decided to throw it into US Cleaner to see if there was any crap under big chips. Now after cleaning and drying it up the board is a little different. Now it seems it's power cycling. No fan spin nor quarter fan spin but CPU coils keep pulsing like if it's trying to turn on. PLT_RESET_L seems to pulse also.
 
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