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submerged Macbook A2141 - no power on, no voltages

S

Sanevent

New member
I tried to inject voltage to PPBUS_G3H Yesterday. As recommended i started with 1v and set a limit of 0.5a at first.

With 1v injected nothing could be observerd. My lab bench power supply was showing that no power was consumed at all. At best i get a reading of 0.001a on my PSU but most of the times it stayed 0.

I soldered 2 wires to one of the big electrolytic capacitors that connect to PPBUS_G3H as well as to GND.

My next step would be to step up the voltage until i can see something, but the small/absent current draw made me unsure if i should.

Because if we had a short, or at least a partial one, at least a bit of current should be drawn.

I tested my solder joints in continuity mode, and they are good. I tested from the end of wire to a different exposed point on the board.
 
2informaticos

2informaticos

Administrator
Staff member
"set a limit of 0.5a at first"
Where I told you to set such limit???
The board will take the current dictated by the low resistance to ground.
It will be low anyway, but don't set a limit!
If lab PSU will detect an overcurrent, wil get blocked and doesn't inject anything; unless knows to work in constant current mode.

Arriving to 5V it should take 0.5A more or less.
That may be insufficient to find a hot spot with the fingers; but easy detected by IR camera.
With 10V the current should be around 1A, or more; 10W should be found even with the fingers.

I hope you didn't forget to check continuity between PPBUS_G3H and any coil.
More than 2V can kill PCH, CPU, or GPU.
 
S

Sanevent

New member
Sorry for the confusion, let me clarify. Of course I'm using my PSU in CV mode - at first set fixed to 1v.
I just need to set an upper limit for the amps, because my PSU can only detect overcurrent when I set that limit, because mine does not do it by itself.
I do not use a CC PSU - I just set the ampere limit to something that felt reasonable for me.

Is there general advice on how to set the current limit correctly?

Before proceeding today, I will check every coil again and then crank up the voltage step by step.
I do have a Thermal camera, so maybe I can find something.
 
2informaticos

2informaticos

Administrator
Staff member
Set always amp limit to max, when injecting voltage.
If you adjust the voltage, can't adjust the current at same time.
The current depends by the value of the resistance to ground.

We don't have any interest to reach the PSU amp limit.
If resistance is low, high current can be achieved with low voltage.
If current limit is too low, PSU will get blocked and doesn't inject the desired voltage.

BTW, a good lab PSU for voltage injection, should support 20A.
 
S

Sanevent

New member
Ok. I tried to inject some voltage today and was met with a very stange behaviour of the board.
I tried to raise the voltage - at first to 2, then 3 and finally 5 v but I got the same result.
The first few moments ( not even a second) the board draws some current, but then it falls back to 0. Flat 0.

As I tried with 5 v I got 0.077a but only for a brief moment before going back to 0.000a.

I did not try to go further, as I was not sure if this behaviour is expected or not.
I thought this was rather strange, because I would expect the current draw to be constant. However this is not the case.
 
S

Sanevent

New member
Im probably as confused as you are. Before injecting voltage it was 15 ohms. Now it starts with 200 ohms increasing to 3mohms.

The only thing i changed is that I soldered 2 wires to the board to inject the voltage and i removed the F8400 fuse before doing so.

After removing the fuse (and before i injected voltage the first time) i checked both pads with the multimeter - because i was curious if that changed something.
The PPBUS_G3H side was 15 ohms and the other side was n.c..

Then i injected voltage as recommended and now the situation is as I described in my last post.

By the way, the new Chip has arrived. I can replace it as soon as im back at the lab.
 
2informaticos

2informaticos

Administrator
Staff member
No reason to inject voltage at all, if no low resistance to ground.

Always allow 10-15s before checking in diode mode (or ohm scale), since power was removed.
Remanent voltage changes real behavior.
 
S

Sanevent

New member
When I came into the lab this morning, the first thing I did was to measure again. The board was without power since Friday.
I checked in diode mode, and when I put the red lead on PPBUS and the black to GND, I get a value of 0.00 and rising well above 1.1 and when I reverse the probes (after waiting a few minutes), I get 0.400 as a reading.

My best guess is, that the short burned itself free somehow and is no longer present - at least this is what I could imagine. I don't know how to verify my theory though.

Is there anything I could check before bringing the fuses and the IC back to make sure that the short, which magically disappeared, will cause no problem if I restore the state of the board?
 
2informaticos

2informaticos

Administrator
Staff member
"I put the red lead on PPBUS and the black to GND"
Almost not used this configuration.

0.400 is a good reading.
Put back the components and test the board.
 
S

Sanevent

New member
I put everything back, including all fuses and the IC. I measured again in diode mode from PPBUS to GND, and the value has not changed. It still is 0.400, which I suppose is good. Can I now safely plug in the charger and test for 20v, or is there anything else that I need to perform first?
 
S

Sanevent

New member
So i measured where i left off last time:

PPBUS_G3H - 12v
PP3V3_G3H_RTC_X - 3.3v
CHRG_EN_MVR - 5v

This is good—yay, first success.
I tried to reassemble the mac and test of that solved the issue - of course not.

First I tried to measure the Input voltage and then a line we already spoke about earlier:

PPVBUS_USBC_XX stays 5v
PP3v3_G3H_T is 1.2v

I suppose that this should not be like this.
Because I also do not receive 20v on my charger - so that's another issue I guess.

I tested everything with and without the battery, but I think the battery will be dead anyway. Can I run the mac without connecting a battery or is this necessary to be able to turn on the system?
Furthermore, is it worth trying to revive the mac with another, or do we still have a hardware issue?
 
2informaticos

2informaticos

Administrator
Staff member
You should diagnostic the board alone on the desk.
But you need 96W, or 140W charger and correct cable.
Be sure the charger is correctly recognized on other Mac.
I recently had problems finding good cables for such power.
These cables are electronically marked.

This board doesn't turn on without battery and charger less than 96W.
So you need to have for sure 96/140W charger, without battery.

However, normal 61/87W charger should switch to 20V; good enough for test in this case.

Check if all ports have exact same behavior; flipping charger cable also.
If any port has different behavior, there should be a problem.
 
S

Sanevent

New member
I have both at hand - a 96w and a 140w charger with the original apple cable.
I tested all 4 ports with both chargers in each orientation and got no luck with that.
I also tested it with a properly rated Thunderbold cable.
No port did anything different. I was not able to archive 20v with any configuration.
 
S

Sanevent

New member
The PP3V3_G3H_T still has 1.2v on every port in every rotation. I just double checked it.

The P3V3G3H_EN however is 0.0v on all ports in all orientations.
 
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