820-00165 "Fan spin Loop from Hell" SO on/off about 1-2 seconds.

[KC Micro Tronix]

I have a board in my "Toy Box" that I just can't figure out. Was hoping for guidance on the dreaded Fan Spin Loop

The board will enter a S0 state and boot up for about one or second then shut down. It will not attempt to enter S0 again and will just sit there sipping 20 mA. Power cycling will start this process over again. When the S0 is on power consumption appears normal 400 ish mA.

I checked the current sensing resistors for both battery and power adapter. Everything is good.

I have checked every S0 rail one at a time during the brief one second it is alive and all S0 voltages are normal. I also checked resistance and everything appeared normal. I am thinking it has to be a sensor shutdown of some kind.



Does anyone have a fan loop check list? How do I move on from here?



* My "Toy Box" is stubborn boards I come back to in a attempt to learn from and if I am lucky I fix one now and then. I try to not use these as donors.

 

[JohnB8812]

Any history liquid drop etc? Does it constantly cycle or only once?

 

[KC Micro Tronix]

• possible liquid damage
• only cycles once as stated in post.

I have spent quite a bit of time with the board under the microscope. Tilted on it's side, looked at all areas and angles. What ever liquid damage that is present is not detectable with visual observation. What I am after here is a road map for these types of faults. I really don't know what to check next.

 

[JohnB8812]

Does the fan go on off on or just on then off and nothing after that?

 

[2informaticos]

Did you try to start in SMC bypass?
Also try known good working BIOS, just in case.

 

[KC Micro Tronix]

• Yes only cycles into S0 mode once as stated in the post.

The unit goes into S0 mode "fan spins for 1-2 seconds" then drops to S5. It does not enter S0 again until you power cycle it. SMC is sending green light signal and turning S4/ S0 rails as it should. Seems like the SMC is working but there is a sensor alarm that is shutting it down. I just don't know how to run those sensor alarms down.

I do not know how to start it in SMC bypass. I know my charger cable is running off a bench power supply so it does not really care if the SMC says to turn on or not. I just get a light to know if it is talking.

 

[JohnB8812]

Gotcha yeah next thing would be SMC bypass. Inspect closely for liquid especially U1900, U1950, U6100 and traces/resistors etc

 

[KC Micro Tronix]

how does one do a SMC bypass?

 

[2informaticos]

Press power button, connect charger and maintain pressing 5-10s.
Or use Google...