MacBook Pro 13inch 2017mid (A1706 820-00923-A) - liquid damage - USBC and Display short circuit

[rilley]

If there was liquid damage in the LCD connector, CPU is most likely damaged anyway as a result of backlight rail arcing with eDP AUX line.

Hello Piernov, thank you for the input.

The only damage that I saw on the board with a magnifier, was on the pin PP5V_S0_ALSCAM_F on the display side, and on the board, and resistor L4004 burned.

And I've checked, I have PP5V_S0 = 5,1v.

Should I remove the heat sink from the CPU to see if everything is intact?

[rilley]

I tried to debug why PP1V8_S0 = 0 Volts

See attached PDF with the analysis.

I think it has connections with PP1V8_SUS which comes 0v from U7800

And also it has missing components (attached a photo with the board), not sure if it helps as PP1V8_SUS_REG_R is 0volts that comes from U7800

From my understanding if I don't have PP1V8_S0, then ALL_SYS_PWRGD is low (0volts), then the whole system can't continue booting, right?

[reformatt]

Usually this data line is shorted after liquid damage to J8500. Should still boot, but you won't get an image. Very common fault.

[rilley]

Usually this data line is shorted after liquid damage to J8500. Should still boot, but you won't get an image. Very common fault.

At the moment I'm trying to boot it up without display and any other major peripherals.

And from my understanding, I'm stuck at missing: ALL_SYS_PWRGD and missing:
PP1V8_S0
PP1V8_SUS

[rilley]

Usually this data line is shorted after liquid damage to J8500. Should still boot, but you won't get an image. Very common fault.

Did two measurements, multimeter in resistance mode at 20k unit, black probe at GND, and red probe:


EDP_INT_AUX_N
4,68

EDP_INT_AUX_P
4,62


EDP_INT_AUX_N
4,64

EDP_INT_AUX_P
4,59

[reformatt]

PP1V8_S0 is derived via a load switch from PP1V8_SUS, which in turn is generated by PMIC U7800. Enable is PM_SLP_SUS_L (measure at R1458), output is via L8020. Check for low ohms etc on the 1.8V lines, especially around touchbar connectors.

[rilley]

What I found so far:

Part 1:
====================================================

PM_SLP_SUS_L = 3,35v

R8024 is not on the board, along with R8029, C8029.
>> but it seems that there weren't anyway, I think nobody remove them, doesn't seems to be trace of flux or heat there (see attached photos).

So my understanding is, without that R8024 it can't convert the P1V8SUS_SW (AC) to P1V8SUS (DC) needed for PP1V8_S0.

PP1V8_S0 measured in resistance mode, and is not in short.

I don't have an oscilloscope, measured P1V8SUS_SW with multimeter in AC set to 2v unit, and got: 0,016 (not sure if this is relevant).

Part 2:
====================================================

Missing component from the board R5400, I can see from the board that it was removed from there (by the old service that I've employed a long time ago).

Attached photo for more context. From my understanding this is the main entry point to power-up the CPU stuff. I have PPBUS_G3H =13V there.

PPBUS_HS_CPU is not in short (measured with multimeter resistance mode at 20k and I have 6kOhm and going up).

>> I guess they removed that R5400 to do measurements, I think..

--------------------------------------------------------------------------------------------
What do you think? (I'll continue debugging)

[rilley]

Could it be that this PP1V8_SUS is generated somewhere else and I need to dig elsewhere and not on the U7800 ?

( seems like the R8024 is not on the board, along with R8029, C8029 will definitely will not help to go further with PP1V8_S0, but from what I saw on the board, there are places that are missing components, but I think they are not there by Apple and nobody removed them [like old repair shop], see the red circle from the past photos that I made with the board, seems like there are small circles with flux ).

Also, without PP1V8_S0, and PPBUS_HS_CPU, then I won't have ALL_SYS_PWRGD anyway, right?

[mon2]

No. The red circled areas are machine deposited solder paste areas using a smd stencil with aperture openings. That is, the paste was applied at manufacturing time but the parts were marked as do not populate.

[reformatt]

R8024 and R5400 are for current sense; it should just read as a short and aren't physical components. R8029, C8029 are NO STUFF in the schematic, so not fitted during production.

PP1V8_SUS is generated from U7800 (3 of 10), no where else. Check that resistance to ground at L8020 isn't short or low. Then check all your signals going in: PP3V3_S5, PP5V_PMICLDO, PM_SLP_SUS_L. Its a buck converter, so you also check the feedback components R8025, R8020, R8021, C8020. The PMIC shouldn't be underfilled, but if it got liquid damage under it, it may need to be removed and reballed.

[rilley]

Thank you Mon2 & Reformatt for your prompt response and for helping me out!

Did some measurements:

PP5V_PMICLDO = 5,13v (at C8025 and at the test pad) - OK
Feedback positive resistance has 10ohm (R8021) - OK
Feedback negative resistance has 99ohm (R8020) - OK

GND and L8020 resistance has 2kOhm (at P1V8SUS_SW bottom side of the inductor) - I think is OK
L8020 resistance as inductor on both sides (has continuity) - I think is OK

PP3V3_S5 near U7800 ( C8020 ) = 3,35V - I think is OK
PP3V3_PMICLDO ( at C7839 ) = 3,2V - might be to low? I can re-do the measurement tomorrow.

PM_SLP_SUS_L ( at test pad ) = 3,35V - I think is ok?

PP1V8_SUS ( at C8023, and test pad, and C8022 ) = 0V - this is the missing one..
>> this has continuity from test pad C8022( PP1V8_SUS ) to P1V8SUS_SW ( R8024 is actually a bridge in PCB, no resistor there )

P1V8SUS_SW ( at L8020 ) = 0V - this is the issue

PPBUS_G3H ( from C8002 ) = 13V - OK

PPBUS_HS_CPU ( at C7960 ) = 0V --> could it be related to this and the missing R5400 shunt resistor and has correlation to U7800 and my missing PP1V8_SUS ?

PPBUS_G3H (at C8013 ) = 13V - OK

PP3V3_S5 ( from C8021 ) = 3,2V - OK?

Test pad at P1V8SUS_PGOOD = I think is low, 0v, was very hard to measure this one, pin too small on the PCB board.

R5400 missing shunt resistor, on the schematic I see it should be there, but on the actual PCB board is removed, I do think someone removed that one as I see traces on the PCB board, I've attached a photo in earlier comments yesterday.

>> anyway, if I put a wire at R5400 ( between, PPBUS_G3H and PPBUS_HS_CPU ) will this help? Could I get damages? ( I understand there are some realtime measurements at ISNS_HS_COMPUTING_N & ISNS_HS_COMPUTING_P )

>> could it be the missing R5400, could lead to missing PP1V8_SUS from U7800 ?
>> if no, and the U7800 has damages, can I create my own convertor buck and inject that 1,8v to the circuit? ( I think this would lead to enable manually the P1V8SUS_PGOOD )
>> at the moment, I don't have hot air solder machine, and it's harder to play and remove the U7800 chip, I could go to someone, and he could only heat it up and press it a little bit more so maybe it helps to connectivity, but to reball it I think it's harder for me :S

Want to mention, C8022 and C8023, they are a little bit swollen, not that much, but I can see them with my magnifier, measured them for short, it has 1.9kOhm respectively 2.0kOhm, so I think they are ok, i think.

Will need to go to someone who has an oscilloscope to measure better the U7800 and P1V8SUS_SW..
>> I've looked closer near U7800 with my magnifier and I don't see physical damages there.

PS: I didn't measured in realtime the P1V8SUS_FB_P and P1V8SUS_FB_N for voltage, as the circuit is too small there and I might short things up there, I will try to go to someone that has oscilloscope and maybe he might be able to help with the measurement there.

Thank you!

[rilley]

Also measured right now the:
C8020 - resistance, 7kOhm.
R8025 - resistance, 99,9Ohm.

[rilley]

What I also did right now:
- disconnected board from power supply
- multimeter set in DC mode at 2v unit
- black probe on GND board
- red probe on P1V8SUS_SW (at L8020), while keeping the red probe, connected the power supply -> no change on the multimeter, 0V

- another test similar as above, but red probe this time on the positive feedback at P1V8SUS_FB_RC from R8025, connected the power supply -> no change on the multimeter, 0V