Another 820-2936 Fan spins 2 sec

[Bohmmen]

I get 12.6 volt on both sides. It was only that pin on u7400 that looked bad. But almost all joints around u7400 look a bit poorly soldered. There are many pads that doesn,t hav solder up on the side on the chip.

Can the problem be caused by a bad u7400. Should i try to replace it?

 

[dukefawks]

It could, but I have never seen U7400 fail. Lets say 5% chance......
I would suspect something wring with SPI ROM first. Measure all pins of it on diode mode and compare to working board.

 

[Bohmmen]

same numbers on SPI ROM on both boards.

 

[Bohmmen]

all S0 and S3 rails goes high when fan spin

 

[dukefawks]

I am out of ideas on this one. Most likely corrosion somewhere. If you can take HiRes close up pictures of the board I can have a look..

 

[ALB-Repairs]

I Would try replace the SPI with one from a donor 820-2936 board. You dont need to worry about ME region on 2011 years so you can just pull the EFI of a donor board with no reprogramming.

You also need to inspect u2800. U2800 drives the clock signal for the PCH and therefore is important when looking at quarter fan spin.

Check R7051 and R7052 and all corresponding traces. This is current sensing for the battery and can sometimes cause quarter fan spin symtoms. After doing all of the above you are looking at a failed PCH.

 

[dukefawks]

You most definitely need to worry about the ME! For testing it does not matter but it does cause issues.