820-00165 Fan Spins, No POST

[brunomotter]

Hello. Got this board here. Board is completely clean, no corrosion at all. Fan spins, I get 1v05 and 1.8V at CPU VCORE, no chime, no POST. Fan spins at max after some time, CPU gets warm. Tried reballing SMC, no luck, tried new BIOS, no luck, verified all SPI resistors and all read ok. No visible broken traces, as I told, board is really clean, no corrosion in any regions. Tried also heating PCH/CPU with Amtech flux with hot air station at 320 degrees for 20 to 30 seconds to make the flux flow under the chip and board is the same. Diode mode on L7630 is 0.126 and I have steady 1.05V on it. Any ideas?

 

[2informaticos]

Check all voltages from page 11.
Be sure the resistors from LPC bus are good.

 

[brunomotter]

R1540 - 33 ohms
R1541 - 33,4 ohms
R1542 - 33,2 ohms
R1543 - 33 ohms
R1544 - 33 ohms

L1270/75/90/95 - 1.05V

 

[2informaticos]

Did you check the voltage on the output pin of the coils?
Do the same with R1280.

PLT_RESET_L comes high?

 

[brunomotter]

PLT_RESET_L - 3.325V
R1280 - 1.05V on both pins. Yes, measuring on pin 2 of the mentioned coils

 

[2informaticos]

Looks like CPU internal problem.

 

[brunomotter]

Was what I thought... Any way to confirm it?

 

[2informaticos]

Unfortunatelly, this is not an exact science.
We don't have the test equipment which has the manufacturer in the production line.

Once we've checked the usual suspects, not much can do on it.
A simple corroded/broken resistor can cause the same symptom; can be a nightmare to solve such a failure.
Is no way to know what kind of failure can cause any resistor from the board...