MBP A1286 820-2915 green light only, no start

[blazzelia]

Hi guys,

I have this 2011 MBP - the company I was working for, bought it at the time for a project and gave it to me after that. Later on, I gave it to my daughter which used it for normal internet browsing and office apps. At some point the, now famous, AMD GPU issue hit this laptop as well. I disabled the use of the AMD GPU following some information I found at the time (the one that, at the end, one moved AMD kext drivers to a backup location). So the laptop was using the CPU graphics and it was ok for the said daily usage. I even replaced the drive with an SSD one and it was operating quite decently.
About an year ago the laptop died. It was not charging the battery anymore (green light only) and, when a start was attempted, a click sound was heard from the inside. I had no time then to look into it but now I would actually need it again for one of the projects I'm working on so I'm tempted to fix it if possbile. I bought some donor mobos from the flea market and I think I have a good chance to fix it if I get the proper direction from someone with experience in Apple laptops. I'm good with replacing chips, I have the proper tools, however I'm not familiar with Apple stuff.

So, as I said, green light only, the battery is dead (0.4V on it), laptop not starting, no fans moving, not even the click noise I heard a year ago. Obviously, I did some reading and start measuring some voltages but at some point I did not know where to go next. I know there is a pulsating voltage somewhere where it isn't supposed to be, but I don't remember the name of the rail. I guess that, at some point, it's going to show up again...

Now, if someone has the amability to help me with it, I would appreciate it.


Thanks,

B

[mon2]

Measure and share the voltage to ground measurements of:

PPBUS_G3H ; F7000 (check both sides)

SMBUS_SMC_BSA_SCL ; at the battery connector
SMBUS_SMC_BSA_SDA

Use DC volts mode on your meter (not diode mode).

[blazzelia]

Hi,

PPBUS_G3H - 12.5V
F7000 - I only see F7040 and F7041 in my board schematic, both connected to PPBUS_G3H, both ok, 12.5V on both ends
SMBUS_SMC_BSA_SCL - 3.4V
SMBUS_SMC_BSA_SDA - 3.4V


Best

[mon2]

Are you using the original 85W power adapter?

[blazzelia]

Yes

[mon2]

Share the voltage to ground of ALL_SYS_PWRGD. Use DC volts mode on your meter (not diode mode).

[blazzelia]

ALL_SYS_PWRGD - 0V

[mon2]

This implies you have at least one power rail that is not good. Go through the power rail tree that is being monitored to determine which rail is failing.

[blazzelia]

PP3V3_S5 - oscillating
PP3V3_S0 - oscillating
PP1V05_S0 - 0V
P1V5S0_PGOOD - 0V
P1V8S0_PGOOD - 0V
P5VS3_PGOOD - 0V
CPUVCCIOS0_PGOOD - 0V
PVCCSA_PGOOD - 0V


So I went on the PP3V3_S5 line which comes out of Q7260 through L7260 and I'm lost here ... P3V3S5_TG is oscillating, PPVIN_S5_HS_OTHER_ISNS is a solid 12.5V, P3V3S5_DRVL is oscillating.

[kevingill]

What does PP3V3_S5 measure in resistance to ground?

[blazzelia]

It starts with a few MOhms, then quikly drops and stabilize around 19 KOhms.

[kevingill]

Do a check on all the power rails to see which one isn't coming up. The critical ones are in the schematic.
Start at S5, then S4, etc.

[blazzelia]

Here they are:

PP5V_S5 - osc
PP5V_SUS - osc
PP5V_S3 - 0
PP5V_S0 - 0


PPBUS_G3H - 12.5
PPVIN_S5_HS_COMPUTING_ISNS - 12.5
PPVIN_S5_HS_GPU_ISNS - 12.5
PPVIN_S5_HS_OTHER_ISNS - 12.5
PPDCIN_G3H - 16.7
PP3V42_G3H - 3.4
PPVRTC_G3H - 3.4

PP3V3_S4 - osc
PP3V3_SUS - osc
PP3V3_S5 - osc
PP3V3_S3 - osc
PP3V3_S0 - osc

PP3V3_T29 - 0
PP1V05_T29 - 0
PP15V_T29 - 0

PP1V8_S0 - 0
PP3V3_S0GPU - 0

At this point I stopped with the 1.8V/1.5V/1.2V/1.05V rails ...

osc = oscillating up and down

[mon2]

Remove all power. Meter in resistance mode.

What is the resistance to ground (in ohms) of these osc rails?

PP5V_S5 - osc
PP5V_SUS - osc

[blazzelia]

PP5V_S5 - 100K
PP5V_SUS - 290K

[mon2]

Not shorted. Check the EN pins on the regulator IC that creates the above rails. Are they also pulsing? Check if you are missing any current sense resistors which can result in the regulator believing there is a too high of a current draw since the feedback is missing and will power cycle the rail(s).

[kevingill]

It's looks as though it's trying to get to S0 with PP3V3_S0 pulsing. However, PP5V_S3 is at 0. I'd take a good look around U7201 to find out the issue.

Have you removed all non essential cables/RAM/etc?

[blazzelia]

Not shorted. Check the EN pins on the regulator IC that creates the above rails. Are they also pulsing? Check if you are missing any current sense resistors which can result in the regulator believing there is a too high of a current draw since the feedback is missing and will power cycle the rail(s).

Two of the EN signals also pulsing, one in 0V. The current sensing resistors are fine.

[blazzelia]

It's looks as though it's trying to get to S0 with PP3V3_S0 pulsing. However, PP5V_S3 is at 0. I'd take a good look around U7201 to find out the issue.

Have you removed all non essential cables/RAM/etc?

RAM was still in but the signals are the same without it.

I pulled C7205 to measure it - 9.6uF. When I measure the voltage on it (PP5V_S5) there is a clicking noise - I guess it's comming from one of the inductors from the back of the board.

[kevingill]

Have you replaced C9560 BTW?