820-2936 short fan spin

[grmacs]

Initially getting short fan spin on power. When triggering on off, I do get Vcore during fan spin. Fan spin lasts a couple seconds. Get full fan spin in SMC bypass mode.

 

[2informaticos]

So the board stays on in SMC bypass mode?
In such case, check all SMC sensors, at pages 49/50.

 

[grmacs]

I caused a short on this board somewhere and have .016V short on pin 2 of L7630... Is this board trash?

 

[2informaticos]

I think 0.016 reading is good for PCH core.

 

[grmacs]

U7940 was the problem. Board starts again. Went through SMC sensors on page 49/50.
in bypass there are some at 0V.

I get 0V at these:

SMC_GFX_VSENSE/ISENSE
SMC_CPU_ISENSE
SMC_CPUVCCIO_ISENSE

 

[2informaticos]

0V shouldn't be a problem.
SMC can stop the board if detects an above limit error.

 

[grmacs]

BMON ISENSE at 3.45V would that cause shut down? schematic says max 3.3V?

 

[2informaticos]

More than sure.
Check resistance between pins 17/18 of ISL6259.

 

[grmacs]

2.7 ohms at pins 17,18 ISL

ISL bad I assume?

 

[2informaticos]

Check components in SMC_BMON_ISENSE area.
Its level should be lower.
Post CHGR_BMON also.

 

[grmacs]

Almost all components for the circuit are NO STUFF, R5422 checks out.

CHGR_BMON is 3.45

 

[2informaticos]

It is very high!
Did you check resistance directly between pins 17/18???
Check their traces and solders.

 

[grmacs]

Yes. Above it's at 2.7 ohms at pins 17/18> I'll swap the ISL and see if it changes

 

[grmacs]

CHanged the ISL and now boots.

As always THANKS!

 

[2informaticos]

You're welcome!

Try to understand what a signal means, then you will know the way to go.