820-3115 - Quarter Fan spin

MUUK

Member
Minor liquid damage.

Fan spins for a couple of seconds then repeats.


PP5V_S3 jumps from 0.2 to something as fan goes on and off
PP5V_S0 jumps from 0.6 to something as fan goes on and off.

Cannot see anything on either of these lines that is suspicious.

Diode mode PP5V_S3 0.430
Diode mode PP5V_S0 0.389 (matches donor)

Wanted to see if it was the S3 or the S0 causing the issue. Removed Q7860. With Q7860 removed PP5V_S3 is 5v.
Suspected Q7860, replaced it.
Board turned on for 30 seconds with normal fan.
Unplugged, waited and tested again - Back to same problem, quarter fan spin.

Vcore when quarter fan spinning is not coming on.

Begin to suspect U7400 ?
Appreciate any help as always.
 

MUUK

Member
Both look and measure ok (180K and 150k).

On pin 2 (input) i get a totally steady 12.56v
On pin 1 (both, seperatley) I get 12.33v, which jumps (very quick change on multimeter - decimal point jumps about with fan pulse)
 

MUUK

Member
ISL looks fine. 4ohm and 20.4ohm on the readings.

Do get pulses at the big coils PP1V5, PP5_S3 etc. Nothing on CPU ones.

No change in SMC bypass mode.

Wanted to see if it was the S3 or the S0 causing the issue. Removed Q7860. With Q7860 removed PP5V_S3 is 5v.
Suspected Q7860, replaced it.
Board turned on for 30 seconds with normal fan.
Unplugged, waited and tested again - Back to same problem, quarter fan spin.

Thanks again.
 

MUUK

Member
If i heat Q7860 it will boot a whole OS and run until shut off. I tried replacing Q7860 again, and all the surrounding components.
 

MUUK

Member
Thanks, Was just looking at Q7802. Replaced it (have already replaced R7860/62)
Real head scratcher.
 
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