820-3302 late 2012 imac fast fan spin

Kyle93

Active member
Have a late 2012 820-3302 imac come in for SSD upgrade. Original hard drive defective and needing replacement. During reassembly technician droped screen while unit had power which blew L9100. Replaced screen and L9100 and have picture again but whenever the imac is turned off or in sleep mode the fan spins fast constantly. Everything works perfect including normal fan speed while its running. Checked and everything is plugged in properly.

Could the fan be spinning fast while its turned off or sleep from the hard drive upgrade? Found this post stating that if pins 2 and 7 are shorted the issue should be solved.

https://forums.macrumors.com/threads/bypassing-the-hdd-fan-when-installing-an-ssd.1765854/

Should we try this first or check something else?
 

Kyle93

Active member
If both sensors have good connections what should we try next? Replacing HDD sensor?? LCD sensor is brand new
 

2informaticos

Administrator
Staff member
HDD sensor can be bypassed, soldering corresponding pin to ground; directly on HDD/SSD connector.
You can also run ASD and see what errors pop up.
 

Kyle93

Active member
Ran ASD and everything surprisingly passed. Tried original hard drive just for testing and fan is still spinning fast while off or sleep.

what should I try next? Not sure how it can be hard drive sensor since it?s original hard drive is doing same thing.
 

Kyle93

Active member
Yes. The new lcd came with a new one and also tried the original. Fan does same thing with either sensor.
 

Kyle93

Active member
All connections to the main logic board are good.

Disconnecting the camera does not make a difference.
 

Kyle93

Active member
Ran HW monitor and HDD bay 1 and 2 are reading 130C

From research I have done this model does not use a external thermal sensor like the 27" imac.

What should I try next?
 

2informaticos

Administrator
Staff member
Check around J4530 and U4500 area.
Looks like dedicated protocol is used on J4530.
Check what happens disconnecting it; also try pulling down pin 3.
 

Kyle93

Active member
Fan still fast with it disconnected.

When you say try pulling down pin 3 does that mean run a jumper from pin 3 to ground pin?
 

2informaticos

Administrator
Staff member
If thing happened when dropped the screen, should be cable, or connection issue.
Finally, you can use software to control the fan, like Mac Speed Fan.
 

2informaticos

Administrator
Staff member
Ooops, fan stays on in sleep an S5 state?
That means 12V_S0 always present.
Check Q7950 for short D-S.
PM_EN_FET_P12V_S0 should go down in S5 and sleep mode.
 
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