820-3437 PP5V_S5 voltage jumping around

[MUUK]

820-3437 - looks like it may have been cleaned, so no hints. Green light on charger. No fan spin.

PPBUS_G3H 8.6v
PPBUS_S5_HS_COMPUTING_ISNS 8.6
PPBUS_S5_HS_OTHER_ISNS 8.6v
PPDCIN_G3H_ISOL 16.6v
PPDCIN_G3H 16.6v
PP3V42_G3H 3,4v
PPVRTC_G3H switching between 3.36 and 3.41v


PP5V_S5 - multimeter (fluke) goes crazy get lightning bolt icon indicates 3.4v-34.4v not seen this before

PP3V3_S5 switching between 0.2 and 3,3v with readings inbetween.


U7501

pin 23 8.49v
pin 4 (enable) 0v r7551 measures 0.3ohm
pin 21 (enable) switching between 1 and 3.3v
pin 12 SMC_PM_G2_EN switching between 1 and 3.3v

checked R5198 was showing 68k not 100k changed it, but after still remained 68k

SMC_RESET_L 3.371v @R7100
SMC_ADAPTER_EN switching between 1 and 3v R5185 8.9k


PP5V_S5 diode mode to ground on C7400 1.4v

any ideas ? thank you for you time

 

[dukefawks]

SMC_PM_G2_EN is not stable. This sucks as this could be an SMC issue or it could be that S5_PWRGD goes low. It could be that 3v3_s3 or s0 is shorted. Check for short to GND on R8000,8011,8050,8020. Also check for shorts on all 5V busses, S3 and S0.

 

[MUUK]

thank you duke.

R8000, reading shows no short on pads 1 & 2 0.9v drop to ground in diode mode.

Same for R8011

R8050 measures 0.4ohm as resistance, 0.941v drop to ground in diode mode.
When board is powered voltage on R8050 jumps between 0.4 and 0.6v

R8020 0.731v voltage drop to ground in diode mode

PP3V3_S5 measured at R2042 is jummping from 1 to 3v
has 0.429 v drop to gnd

S5_PWRGD measured at probe point 178 is jumping 1 to 3v, shows OL v drop to ground.

R8141 pin 1 has solid 3.4 PP3v42, Pin 2 has jumping.1v to 3v.measures 93.6k in resistance,
pin 1 0.731v drop to gnd
pin 2 0.401 drop to gnd.

Measuring other rails voltage drop to gnd:

PP5V_S4RS3 1.4v drop to gnd @ C7600,
PP5V_S0 1.2v drop to gnd @R8151
PP3V3_S5 0.429 @R2042
PP3V3_S4 0.369 @C3510
PP3V3_SUS 0.329 @R6102
PP3V3_S3 0.452 @R2040
PP3V3_S0 0.319 @R2041
PP3V3_S4SW_SNS 0.349 @C5480

So with no shorts to ground must it be the SMC ?
Can I try running a wire for PP3V42 to pin 12 of U7501 (SMC_PM_G2_EN) and see what happens ?

 

[dukefawks]

I would go for the SMC first. I have a feeling this one is going to suck

Have you tried connecting a charged battery and see if voltages are stable and if it charges?