820-2879 PPBUS 1V

[No-Clean]

Initially PPBUS was ~1V, I then replaced U7000 and Q7035 I now get ~4V on PPBUS then it starts to drop down close to 0V, loops then next time around starts around 11V then rapidly drops down to 0V and repeats the loop.

Checked pins 17-18 and 27-28 of U7000 and those are fine
3V42 resistance is around 240K after replacing U7000, before that it was like 11k

I've never seen this before, please help.

 

[2informaticos]

3V42_G3H steady value?
Did you try SMC bypass mode?
Replace C7025, just in case; maybe Q7030 too.
Check diode mode to ground at L7220; any voltage pulse there?

 

[No-Clean]

3V42_G3H steady
Replace C7025 same thing
Replace Q7030 same thing
Diode read on L7220 is 0.130 on both ends
Pulse every 7-8 seconds on L7220 ~3V

 

[2informaticos]

Post U7000 voltages; pins 1, 2, 3, 6, 9, 12, 13, 14, 15, 17, 19, 20, 27.
Check the R/C networks from pins 5, 7, 8.
Be sure R7012 is good.

 

[No-Clean]

ISL
1-16v BUT PULSING
2-16.5V
3-4V
9-0.031V
12-3.4V
13-3.4V
14-3V
15-0
17-PULSING 11V then it starts to come down to ~3V
19-5V
20-5V
27-PULSING 16V then it starts to come down to ~6V

17/18- 5 ohms
27/28-22 ohms

R7012 1k Good

Check the R/C networks from pins 5, 7, 8 please explain what to do.

 

[2informaticos]

You said to have 4V at PPBUS_G3H.
If in fact, if fluctuates 3-11V, then SMC can cycle power, because detects something wrong.
Check what happens in SMC bypass mode.

If R7020 voltage fluctuates, you may need to change Q7080/85.
PPDCIN_G3H also fluctuates?
If yes, test with fake charger, or lab PSU and 60/85W Magsafe 1 cable.

 

[No-Clean]

Yes PPBUS fluctuates down from ~12V to ~4V then cycles
SMC bypass I get not light on charger and 3.3V steady on PPBUS
R7020 does fluctuate
PPDCIN_G3H steady ~16V
Replaced Q7080/85 same thing

 

[2informaticos]

Remove F7040 and check C7040 voltage.
Check diode mode to ground at L7220/60.

 

[No-Clean]

With F7040 removed C7040 voltage starts around 3.4V then drops down from there and loops around.
Diode mode reading on L7220 is 0.140 and on L7260 is 0.425 both measured with F7040 removed.

 

[2informaticos]

Check diode mode at L7220 inverting multimeter probes.
Compare with good board.

 

[No-Clean]

Compared with the other boards I have they are pretty much the same measurements.

 

[2informaticos]

Post AVREF_SMC voltage.

 

[No-Clean]

I found an old easier to repair same model board, I fixed that and gave it to my customer, I was pretty much over with this board.