820-00165 enters S0 state but has no CPU vcore

[bjf]

This board has all voltages but has 0V on CPU vcore. No cycling. Just stays at 0. Vcore measures 12Ω to ground. U7200 is getting 5V and 8.6V. Fan does not spin up. Has 5V though. I originally cleaned up an issue with U1950 to get it to go into S0. I attached pre-ultrasonic-cleaning pictures. Not sure where to go next with this.

 

[JohnB8812]

Assuming you removed JTAG? Check resistance between pin 2 of PPBUS fuse and Pin 2 of L7310 before continuing to make sure PPBUS did not short to VCore.

 

[bjf]

No, I didn't remove JTAG. I know it's gospel to pull that thing but I've never had it help and I like having it there in case I need to program the BIOS chip. Regardless, I went ahead and pulled it just now. No change. No short between PPBUS and L7310.

 

[2informaticos]

If has 8.6V, 5V and even other voltages, there is no short to VCORE for sure...

Recheck to see if catch at least a pulse on VCORE.
Do you get 24MHz at Y1915?
Check SPI termination resistors and traces around U6100/01.
CPU_VR_EN tries to appear?

 

[JohnB8812]

Remove the JTAG at All times if it’s corroded. I’d say check what 2informaticos said for sure

 

[bjf]

Went back to the area of most damage and replaced R8151 and R8152. They both measured fine but looked bad and the voltage divider wasn't happening. All good after that. Thanks for the help.

 

[JohnB8812]

Nicely done!