820-3023 Fan runs 100% immediately

[MUUK]

Clean machine, no signs of liquid, boots up does not feel "jerky" when booting

From the moment the power button is pressed the fan runs 100%.

Tried Known good Battery, SSD, DC in, Dc in flex, Track pad, track pad flex and two different fans.

EFI Asd tells me : "Motor is running slower than it should" passes all other test. Can't get the OS ASD to load up.


Q5660
pin 1 3.3v
pin 2 3.3v
pin 3 4.58v

Replaced Q5660, R5665, R5660, R5661 no change. Tested continuity in all this area and seems fine.

Damaged trace to SMC ? Would be grateful of any hints!

 

[dukefawks]

SMC is not seeing the tacho signal from the fan. Check SMC_FAN_0_TACH and the resistors. Also diode mode on this line.

 

[MUUK]

Thank you duke.

Diode mode to ground for SMC_FAN_0_TACH (R5665 pin 1) 0.56v

Voltage on SMC_FAN_0_TACH when turned on is 3.146v (both at probe point near SMC and on R5665 pin 1)

I replaced R5565, R5660 and R5661 again checked continuity round this area, no change.

Thanks for any help you might give!

 

[dukefawks]

Tach signal can be viewed on a scope, see if there are pulses there. Also check diode mode on SMC_FAN_0_CTL

 

[MUUK]

Thank you Duke. It has continuous regular pulses on SMC_FAN_0_TACH.
Diode mode to ground on SMC_FAN_O_CTL is 0.550v

 

[dukefawks]

That does all seem fine then. SMC seems like the next suspect if you are sure that the fan and connector makes good contact.