820-3437 Fan spins twice but no chime, no screen

[phuketmymac]

Hello,

First general question... why can't search the forum based on board numbers? ;-)

Second, I have that 820-3437 board that someone has already reworked and cleaned so difficult to tell if any damaged has been done on it.
However what I can tell is that I am getting the fan to spin only twice or once (when it should do thrice)
All the power rails are present, as well as SYS_PWROK_R and PM_PCH_PWROK
CPU gets hot.

Any hint please on where to look in this case?

 

[gcain]

You can, just omit the - as that is search syntax for ignore.

So search for 820 3115 or even just 3115.
820-3115 means 820 and NEVER 3115.

Welcome!

 

[dukefawks]

Check termination resistors from U6100 to the SMC

 

[phuketmymac]

Hi Duke,

I did check these and they measure all fine.
I've also reflowed the SMC in case of a bad connection underneath it but no cigar.

I also tried a different BIOS chip.

Any other idea please?

 

[dukefawks]

Not much can be done. Check resistors and traces again from U6100 to the SMC. Inspect board for corroded/missing parts

 

[phuketmymac]

That board can stay running forever, fan spinning however when I try to measure the voltages near U1950 the board just dies.

Could I be on a hint or is it a normal behavior? (thinking it could create a slight voltage fluctuation which would cause the CPU to stop...)

 

[dukefawks]

Is normal that it shuts down when probing around U1950. But why probing around U1950, if you have CPU Vcore all power sequence is working.

Check U6100 area and termination resistors and the traces.