820-3115 no cpuvcore

[Gmorb]

as stated no voltage for cpu. board had very unnoticeable water damage as if its been cleaned.

one of the ton resistors (r7403) was giving a wrong resistance changed it even changed u7400, Q7510, Q7520, Q7550. Checked traces from ton resistors to u7400 and nothing was wrong there.

yet no changed i still get just a high fan spin no cpu. what should i try next?

 

[2informaticos]

First check if 25MHz try to appear at pin 9/U2600.
Do you notice any drop pulse at TON pins of U7400?
Does it receive enable signal?
Next check SPI resistors termination and traces around SPI chip U6100.
Also try new BIOS.

 

[JohnB8812]

If one of the TON resistors was bad, it would probably be good to replace U7400.

 

[Gmorb]

25mhz is present compared to a known good and voltages are the same.

no drop in pulse on ton resistors if by enable signal you mean u7400 is recieving vcc, yes it is. Ton resistors are recieving its 12.5v on one end and half a volt on the other.

i am getting voltages on u6100 so all traces are good there.

now i think the cpu is dead on this. When measuring on an o scope i get voltage bursts up to 16v and cpu is getting hot.

 

[2informaticos]

"12.5v on one end and half a volt on the other."
Looks like CPU power supply is working...
Check again voltages on its coils.
Usually 0V at AXG after few seconds, but VCORE should have aprox 0.75V when board works.

 

[Gmorb]

neither cpuvcore nor axg is showing any voltage. like i said when i used the oscope i could see up to 16v spikes on cpuvcore so im thinking maybe the thing is fried. whats your take?

pin 27 of u7400 is not producing any voltage on a known good i get voltage out of it and EN pin is getting 3.3v i have replaced this u7400 3 times now same result.

 

[2informaticos]

"i could see up to 16v spikes on cpuvcore"
You may want to check the other pin of the coil; there shouldn't be any high voltage spike...

Did you try new BIOS?