A1502 2015 820-4924 no power

[iMuhtaseb]

board came in cleaned up from a previous technician.. after examining the board visually I've seen some work done on the EFI/firmware..
I've taken the chip out and it reads ok on Mac EFI Toolkit, I can read the SN and other information normally..

I have taken a look into the board and I could not find anything suspecting.. I tried to look for corroded chips or corroded caps even to see if there's any areas damaged by liquid and I could not..

I've taken some measurements:

PPBUS 12.6
PP5V_S5 present
PP3v3_S5 present

S4 rails when the problems happen..
PM SLP S4 L not present (0.200mv).. although it powers on when I plug in the MagSafe power adapter and it shuts down after 2 attempts.. (S0 rails do that as well as I mention down below)
PP5V_S4 not present (no shorts)
PP3v3_S4 not present (no shorts)
The only rail I've seen a low diode mode readings compared to flexBV is PP3V3_S3RS0_CAMERA and I cannot precisely know if this is the real cause of not..

Measuring further
PP5v_S0 is present when I plug the MagSafe power adapter and it shuts itself down to 0.400mv.. no shorts and diode mode good
PP3v3_S0 is present (shouldn't be off since S4 is not present? this is weird no?)

bench PSU shows a 0.120 to 0.320 milli amps consumption when I plug the MagSafe power adapter then it stays 0.02 without consumption afterwards..

this is a tough and I cannot pinpoint exactly which signal or line is missing

[mon2]

PM_SLP_S4_L is an active low signal. If this signal is at 0 volts, this signal is true.

Remove all power. Meter in resistance mode. Measure the resistance to ground of each inductor.

Test with a known good bios since it was messed with by the last technician.

[mon2]

If required, have access to a number of bios images for this model. Let me know.

[reformatt]

Do you get Vcore during the initial power on? Double pulse is usually bad cpu in my experience on this vintage of boards.

[iMuhtaseb]

I've rewritten new bios with clean me and its still exhibiting the same behavior..
I've measured inductors with resistance mode and couldn't find shorts or low resistance readings..

[iMuhtaseb]

Do you get Vcore during the initial power on? Double pulse is usually bad cpu in my experience on this vintage of boards.

hm.. yes I do.. I have the Vcore and it drops after the second pulse..

[mon2]

Remove all power. Meter in DIODE mode.

Measure the dual common cathode diode @ D7005.

Red meter probe on pin # 1 of D7005; black meter probe on pin # 2 of D7005. The diode should conduct. Reverse the meter leads and the diode should block.

Repeat the tests with pins # 3 & pin # 2.

Post all measurements.

[iMuhtaseb]

Pin 1 with RED pin 2 with black: 2.328
Pin 1 with BLACK pin 2 with red: OL

Pin 3 with RED pin 2 with black: 2.460
Pin 3 with BLACK pin 2 with red: 0.227

Pin 3 with RED pin 1 with black: OL
Pin 3 with BLACK pin 1 with red: 0.226

[mon2]

Replace this part and test again.

Pin 3 with RED pin 2 with black: 2.460
Pin 3 with BLACK pin 2 with red: 0.227

confirms this part is defective.

[iMuhtaseb]

I have replaced the diode and board is still exhibiting the same behavior.. I have compared the measurements I have taken from another board and it reads the same.. the diode readings was and still OK I suppose.

[iMuhtaseb]

Looking into the board using a thermal camera and putting it on power I can see the CPU starts to heat up a little then shuts down.. as well as the camera IC but I guess its associated with the PCH that's why it heats up..

A teeny little warmth is coming from the SMC as well..

[mon2]

With no power to the board, measure the resistance to ground of each pin of this dual diode.

So measure pin #1 to ground; #2 to ground; #3 to ground. Post each measurement.

[iMuhtaseb]

Pin #1 resistance to ground 72 kilo ohms.
Pin #2 45kilo ohms
Pin #3 490 kilo ohms

[mon2]

Check the resistance to ground of the CPU power rails. If too low, the CPU may be defective. The diode measurements are ok.

[iMuhtaseb]

L7320 9.9 ohms
L7310 9.8 ohms
L7630 246 ohms
L1270 244 ohms
L1290 507 ohms
L1275 240 ohm

[mon2]

These all look ok to me.

What is the voltage to ground of ALL_SYS_PWRGD? Does this pulse?

[iMuhtaseb]

4.3 million Ohms in resistance
0.460 in diode mode

there's pulse then it drops to 0.0v