[SOLVED]820-3437, P5VS4RS3_EN Pulsing

[SMMRepair]

Working on an 820-3437 board with no power. Green/orange LED, but no fan spin. CPU does not get warm.

PPBUS, 3v42, vrtc, 5v_s5, 3v_s5 all stable and present. Where things get funky is with the higher-up voltages--pp5v_s0, pp3v3_s0, 3v3_s3, vcore, and p5vs4rs3_en--are all pulsing. They come up for a split second, then disappear. VCORE is present, but pulses along with the other voltages. I tracked back the pulsing, and R8177/R8179 are both pulsing on both pins (s4_pwr_en, pm_slp_s4_l).

I checked for a short on the s5/s4/s3 rails and found none. No liquid to the board that I can find. Inspected very closely under the microscope.

Any ideas where I should go next? All help appreciated!

 

[dukefawks]

The usual, U6100 area and termination resistors.

 

[SMMRepair]

Hey Duke, yeah I checked that area well already. New clock, new BIOS chip (just to check if it will power), no dice. Might throw this one in the parts pile. I posted last year about a "growing stack" of boards with similar issues...this one will join those. Would really love to get these figured out. They're all no-liquid boards, too; or at least, there's zero evidence of a spill. Oh well.

 

[SMMRepair]

Duke, I stand corrected. I wanted to quickly update; I decided to check all termination resistors in the BIOS area just because (last resort--hadn't done so yet), and found SPI_CS0_L was not continuous from one of the test pads to R6125. Ran a quick wire and we have fan spin! But now I'm dealing with an on/off/on/off/on/off issue. Will get back to work and update when needed.

 

[SMMRepair]

Got this one figured out. The clock chip I swapped onto it during my initial troubleshooting was faulty. Replaced that clock and everything is good to go! I've noted to myself to not be lazy and actually check all the termination resistors for SPI ROM, etc. Solved--thanks again, Duke!