820-00165-A, no PM_SLP_S4_L

[Max7]

This one came as no power, very small signs of corrosion, cleaned up, nothing creating short or discontinuity. No green/orange light, no fan spin, no warmth on CPU.

It draws 25mA from the charger hence I checked PM_SLP_S4_L, 3.1 mV

Performed the checks on repair.wiki:

• U1950 is corroded and you can't see it: it looks good I haven't removed it, no corrosion in the area.
• Corrosion on probe points for SPI ROM U6100 area: very clean
• Bad clock chip U1900: nothing visible
• Corrosion on RTC pullup resistors R1300 to R1303 (or C1300/C1303 shorted to ground): Both resistors measure 20K as expected, caps are not shorted
• If you remove R8111 and PM_SLP_S4_L comes back: removed this resistor, no change on PM_SLP_S4_L, put it back.

C7583 was most impacted by corrosion, removed it and not yet replaced as it looked like the smallest of the 4 parallel resistors to ground on that line.

Further measurements:

PP3V42_G3H = 3.42V
PPBUS_G3H = 8.63V
SMC_RESET_L is high
PPVRTC_G3H = 3.433V
RTC_RESET_L = 3.329V
PHC_INTVRMEN = 3.324V
PHC_DSWVRMEN = 3.336V

then PP3V3_S5 = 0.620V !

Traced PP3V3_S5 back to Q7560 (hope this is correct), VIN is fine at 8.6V but VSW (pins 6/7/8) are 0.620V again.

Should I suspect a faulty Q7560 or anything else I can check before changing it ? Just wanted to check I am not travelling too far in the wrong direction.

EDIT: Moving onto U7501, PPBUS_S5_HS_OTHER_ISNS = 1.01V, instead of 8.6V, checking this rail now

 

[2informaticos]

"PPBUS_S5_HS_OTHER_ISNS = 1.01V"
Check R5430 and its traces.

C7583 is not critical, forget it.

 

[Max7]

R5430 is not installed, but the upper pins are reading 8.6v, moreover, C7540/41/42 C7570 all reading 8.6v. Q7520 pin 1 is also 8.6v.
Then C7500, pin 1 reads 1V.

Corroded pads of C7583 (that was removed earlier) are pretty much right on the other side of C7500. It is a bit like 8.6v on the front of the board and 1V on the back. Could it be that one of the pads is actually a via and now acting as a resistor? I may just be making up things.

 

[2informaticos]

You must have the same voltage on that power rail, doesn't matter which side of the board is.
One passing hole is corroded...

 

[Max7]

I think that's the case, between C7541 and C7500 pin 1s it is 0.5Mohm if I didn't measure it incorrectly. Will check again tomorrow. Thanks for the help.