820-00165 quarter fan spin loop

[No-Clean]

Board had corrosion around L1290 when it came in. That got fixed and client used the MacBook for about 2 weeks, then it came back for no power, SMC reballed and back to working, but it only charged with chargers 60w or more.

While working on the charging circuit I managed to fix the charging problem, but now it is boot looping, fan spins for about 1 second stops and repeats constantly.

SMC bypass does the same thing but for that 1 second fan spins a little faster.

Already replaced U7100 and checked pins resistance17-18 and 27-28 both are fine.

Tried clean BIOS, new U6101 and everything around U1950 is clean, SPI resistors and traces are clean.

Rails present:
ppbus 8.56V
ppvrtc_g3h
pp5v_s5
pp3v3_s5
pp3v3_sus

After that all S4-S3 rails are pulsing including VCORE

 

[2informaticos]

Something else damaged by corrosion.
Possibly crap accumulated underneath CPU.

PLT_RESET_L is pulsing?

 

[No-Clean]

PLT_RESET_L not pulsing, this board already went thru UC and oven.

 

[2informaticos]

Check for pulse at pins 7 & 3 of U1950.

 

[No-Clean]

Yes both of them pulse

 

[2informaticos]

What about CPU_VCCST_PWRGD and CPU_VR_READY?

 

[No-Clean]

CPU_VCCST_PWRGD and CPU_VR_READY pulse also

 

[2informaticos]

Pin 3/U1950 pulsing too?

 

[No-Clean]

Pin 3/U1950 pulses yes

 

[2informaticos]

Looks like PCH issue.
Heat it with quality flux.
Try to burn eventually accumulated crap underneath.

 

[No-Clean]

Cleaned glue around CPU, put 559 flux and ran it via the ZaoMao reballing machine and same exact behavior.