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submerged Macbook A2141 - no power on, no voltages

S

Sanevent

New member
Hello there.
I'm new to this Forum and I don't know if I'm in the right place to ask.
I'm working as a forensics examiner for smartphones. I'm very familiar with Smartphones but not with Macbooks, so please be kind to me as I'm trying to learn to repair macs now.

My colleague dropped a Mac on my desk which was bathed in Tea. When I opened it up, all traces of corrosion I expected had already been cleaned off.

With that in mind, I dried the device in a dry box for 2 days and then tried to power it on - with no success.
I removed the logic board and probed the PPVBUS_USBC_X which was 5.124v with no significant change.
I expected 20v here, but that did not happen.

After studying the schematic I tested the voltage lines around the cd3217b12 USB C controller.
Voltages here were:

PP3V3_UPC_XX_LDO = 3.3v
PP1V5_UPC_XX_LDO_CORE = 1.5v
PP3V3_G3H_RTC_X = 0v

It was consistent on all 4 of them.

Please correct me if I'm wrong here, but based on the schematic of the A2141 I assume, that the 3v3_RTX line powers the USB-C controller, which then negotiates the voltage with the charger. This line is generated by the U6960? which is enabled by the CHRG_EN_MVR line. I tested this line, and it was 0v.
I traced back the CHRG line to the U7000.

From her on I lack experience. The only suspicious line I found on that chip was the PP1V8_SLPS2 line, that connects to some kind of enable pin on that U7000. But that line was also missing power.

I tried to get as far as I could, but now I'm not quite sure how to proceed.

I also tested PPBUS_G3H which is also around 0v measured on the F7000 Fuse, in Diode-Mode I measured 0.032v, also on F7000 to GND. The resistance was about 15 ohms.
I'm not sure if this even makes a difference now because the other voltages are missing in the first place - so I assume the main power will not be generated if the other ones are missing. I don't know if this is dependent or not. I also don't know if 15 ohms (it seems pretty low to me) are already shorted or if this is fine.

I would be very grateful if someone could assist me or give me a hint on where I should look next or even what is wrong with the device.
 
2informaticos

2informaticos

Administrator
Staff member
First of all, welcome to the forum!

"I assume the main power will not be generated if the other ones are missing"
Is exactlly opposite as you tought.
All voltages are derived from PPBUS_G3H; excepting 3V3_G3H, which must appear first.

Remove both F7000/1 and check where the low resistance to ground remains; I bet for pad 2.
Compare with the readings (to ground) on all big coils.
Don't forget L9080/580.
 
S

Sanevent

New member
2informaticos said:
First of all, welcome to the forum!

"I assume the main power will not be generated if the other ones are missing"
Is exactlly opposite as you tought.
All voltages are derived from PPBUS_G3H; excepting 3V3_G3H, which must appear first.

Remove both F7000/1 and check where the low resistance to ground remains; I bet for pad 2.
Compare with the readings (to ground) on all big coils.
Don't forget L9080/580.
Click to expand...

Thank you for your Answer and for clarification.
There are a few things to that I need to ask. Im using ZXW and when looking at the available lines I only have a 3V3_GHT_T line. I don't have any other. Are they the same ?

Furthermore, I removed the Fuses as you told me, and I measured from the Pads to GND.
From PPBUS_G3H there still is 12 ohms to GND
From PPVBAT_G3H_CHGR_REG there is around 4 mohms to GND.

Right after that I tried measuring the Inductors. Here I must ask on what readings you expect when you measure them. In my understanding, and inductor needs to be close to 0 ohms between the terminals but not flat 0 (or it is shorted?).
Measuring the coils to gnd gave me roughly the same value on both terminals (as expected based on my assumptions), with varying values to gnd from every single inductor.

My readings on the L9080 and the L9580 were the following:

With Disode mode to gnd - between 0.48 and 0.5v
The resistance of the inductor itself - 0.2v ohms
The resistance to GND ~ 4 mohms

I checked the rest of the inductors belonging to PPBUS_G3H (including the ones in proximity) and all of them had a resistance of around 0.2 ohms from terminal to terminal.
I'm not exactly sure what you mean by "comparing the readings to GND on all big coils".
I think I should measure from one Terminal to GND- but then which values do I expect and what do I compare it with ?
Do they all need to be the same ?

Thanks for your help :)
 
2informaticos

2informaticos

Administrator
Staff member
"the inductors belonging to PPBUS_G3H"
I meant big coils, which belong to secondary power supplies; not connected directly to PPBUS_G3H.

"inductor needs to be close to 0 ohms between the terminals"
Yeah, but I asked about resistance to ground!

"I think I should measure from one Terminal to GND"
If any gives the same reading as PPBUS_G3H, can help to find the culprit.

BTW, write directly into bottom reply box, instead of clicking Reply button.
No need to quote an entire post, visible few centimeters above.
 
S

Sanevent

New member
I measured all of the really big coils. I have some results, but I'm not sure if that's what you had in mind.
(mostly because I don't know what is big for you)

The most suspicious ones were L7701 with ~ 80 ohms and L8102 with ~60 ohms.
I also found a coil sitting between GPU and CPU L7330 which had 13 ohms - just like PPBUS. But here I'm not sure if that even belongs to a secondary power supply ( my best guess was anything related to buck converters ^^)
If you had a certain area in mind or any Idea where else I could look I would be glad if you could specify further.

Just to make sure I also probed some Inductors around the U7800.
I found out that the Inductors L7806 - 9 are all between 13 and 15 ohms. I don't know if this is supposed to be that way.
 
2informaticos

2informaticos

Administrator
Staff member
"The most suspicious ones were L7701 with ~ 80 ohms and L8102 with ~60 ohms"
Suspect why?
The problem can only come from a coil with very similar reading; and not bigger at all.

"L7330 which had 13 ohms - just like PPBUS"
Now check resistance (ohm scale) between L7330 and PPBUS_G3H.
If you get a reading close to 0 ohm, then remove U7370 and check again; to ground also.

"Just to make sure I also probed some Inductors around the U7800"
None of them is PPBUS_G3H related!
 
S

Sanevent

New member
"The problem can only come from a coil with very similar reading; and not bigger at all."
I think I can see the reason for that now that I looked at the schematic again.

At first I measured 0.02 ohms between PPBUS_G3H.

I managed to remove the U7370 (Although it was very hard because it felt like the chip was 99% GND). I now measure 60 ohms from PPBUS_G3H to GND.
I measured 80 ohms from L7330 to PPBUS_G3H. 3

But from L7330 I still measure 13 ohms to GND.
I don't know if it is supposed to be like this.

As for the U7370 chip - I found a replacement part on Aliexpress. I would just go ahead and order some to replace the probably now-dead part.
 
S

Sanevent

New member
I suppose that's with the U7370 soldered back onto the board?
Because without the IC I got 0.08v to PPBUS_G3H and 0.02v to GND in diode mode.
Currently, I can not check with the IC in place, because it takes some time for the chip to be delivered.

Edit:
I guess you meant PPBUS_G3H to GND - there I get 0.06v in diode mode (also with the IC not back in place).
 
Last edited:
2informaticos

2informaticos

Administrator
Staff member
0.060 in diode mode is still bad, for PPBUS_G3H.

BTW, don't write end "V" for diode mode readings.
Avoid any confusion with voltage readings.
 
S

Sanevent

New member
Ok got it.

Do you have any advice for me, what I can try to do next to find the error on PPBUS_G3H, or should I wait until the new IC arrives to replace it first?
 
2informaticos

2informaticos

Administrator
Staff member
I hope you didn't apply power (nor even battery) on the board without U7370.

Check if any big coil gets a reading close to 0.060 in diode mode to ground.
 
S

Sanevent

New member
Nope, no power was applied to the board. I would not even dare, until I'm not at least 70% sure that nothing blows up or you advise me to try.

I rechecked all big coils. The only 2 candidates that came close were L8102 and LA850, measuring 0.052 to GND. Everything else was far beyond or above the 0.06.
 
S

Sanevent

New member
I checked L9080 and L9580. Both of them have the same values:
0.51 to GND in diode mode
0.46 to PPBUS_G3H in diode mode
2.5 mohms to PPBUS_G3H in resistance mode
4 mohms to GND in resistance mode

If i measure in resistance mode, the Resistance decreases slowly. E.g. if i measure and have 4 momhms to gnd, then i measure 30 seconds later i only get 2 mohms. Could be normal behaviour, i just wanted to mention it.
 
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