Macbook Pro A1708 20V 0A, PPBUS_G3H 13v

[thecookie17]

Hi everyone,
I'm a newbie regarding all this board repair stuff, and have never done it before, but I thought I might give it a try before throwing my logic board out or selling it. Thus I'm apologizing in advance for any stupid questions.
When I first plugged in the meter it showed 20V and 0.01A current draw, however now I have no current draw whatsoever.
I measured PPBUS_G3H with 13V, so that seems to be present.
https://repair.wiki/w/MacBook_Pro_A1..._shorts_repair
I tried everything listed on that page, but everything seems to be okay.
PPBUS_G3H is present, the diode measurement resulted in 0.425V, and the resistance of SMBUS_SMC_5_G3H_SDA and SMBUS_SMC_5_G3H_SDC was not low to ground. (high kΩ region)
Then I measured
PP3V3_S4, I'm not getting anything (0V), but when measuring resistance, it shows me about 1.2 MΩ, which wouldn't indicate a short.
PP3V3_S5 oscillates between 0 and 3V (haven't looked at it with the scope but the multimeter shows it too), PP3V3_S5 has about 700kΩ to ground.
PP3V3_G3H is present however.

I know these measurements might seem random but I've just been trying out everything I read online to this point. Maybe you guys can help me locate the problem further?

[mon2]

Welcome.

Review U7650.

What is the voltage to ground of the following?

P3V3S5_EN ; is this voltage stable or cycling?


Review U8210.

What is the voltage to ground of the following?

PM_EN_P3V3S4

[thecookie17]

Hi, thanks for taking the time to answer.
P3V3S5_EN is indeed cycling between 0 and 3V
PM_EN_P3V3S4 is showing 0V.

[mon2]

Remove all power. Meter in resistance mode.

Confirm that the following traces are reaching the inductor used for the same power rail:

CSP2
CSN2

Place one meter probe directly onto the regulator chip pin (U7650); other onto the inductor @ L7690.

The pulsing of the enable means the logic board is attempting to power this rail on.

[thecookie17]

I'm not sure if I understood you 100% correctly because I cant find CSN2 in flexbv, but I attached a picture which measurement I did.
Result : 10 Ω

PS: I also found out PP5V_S4 is missing.

[mon2]

CSN2 is pin #17 on the same charger IC.

Configure your meter to the lowest resistance mode. Touch the meter probes and report the measurement. This measurement should be ~0 ohms or the lowest resistance that is measured when you touch the meter probes together. Respectively, the measurement from pin # 18 on the ISL chip to pin # 2 of the inductor should also be ~0 ohms (not 10R = 10 ohms).

[thecookie17]

I did check the meter and it has 0.1R. I even grabbed another meter to verify, which has 0.3R , and with both I'm now getting 0R between Pin 17 (U7650) and Pin 2 of the Inductor, however between Pin 18 of the U7650 and Pin 2 of the inductor I'm now getting 1.567kΩ with both meters.
I dunno how that 10R Measurement came to be, I probably must have made a mistake but I double checked now both measurements with both my meters.

[thecookie17]

I just figured out that Pin 18 is connected to Pin 17 (and thus Pin 2 of the inductor) over R7693, so that 1.576kΩ measurement could be plausible depending on the value of R7693

PS: Please correct me if I'm seeing this wrong

[mon2]

Correct. The 2 resistors are effectively in parallel with a resistance of 3k16 each so your measured value is now correct.

[thecookie17]

CSN2 is pin #17 on the same charger IC.
Respectively, the measurement from pin # 18 on the ISL chip to pin # 2 of the inductor should also be ~0 ohms (not 10R = 10 ohms).

But doesn't that contradict your statement, that pin 18 should be 0Ω to pin 2 of the inductor? I'm a litte confused right now.

[mon2]

My correction - Trace one leg and it will be 0 ohms in the path. This should be pin # 17 on IC to pin # 1 or # 2 on the inductor @ L7690.

When using pin # 18 on the IC to pin # 2 or pin # 1 on the inductor @ L7690 - the total resistance will the parallel effect of R7693 & R7692 = ~ 1k567. The inductor will have a resistance but very close to 0 ohms since this is effectively a wire around a bobbin which we are ignoring.

https://www.allaboutcircuits.com/too...ce-calculator/

[thecookie17]

Great, that seems to be all right then. Any ideas on what I could try next?
Thank you for your efforts.

[mon2]

Would you have a USB C meter? Is the USB C port stable @ 20v or is power cycling? What is the exact current draw? 0A?

[thecookie17]

I found out PP5V_S5 is pulsing between 3.5 and 5V according to my multimeter.PP3V3_S5 also pulsing

[thecookie17]

Would you have a USB C meter? Is the USB C port stable @ 20v or is power cycling? What is the exact current draw? 0A?

I do have a usb-c meter and it just shows steady 0A@20V. It used to show 10mA when I first got the board (I bought the macbook off of ebay), then I left it alone to work on other things and now it just shows steady 0A. Regardless 20V is steady.

[thecookie17]

It's funny because it seems to me that my problem is similar to this guy:
https://boards.rossmanngroup.com/thr...-steady.50493/
I just checked for a short on PP1V_S5, and what do you know, 0 Ω
I measured from Pin 1 of those capacitors to ground, that should be PP1V_S5G if i'm not mistaken.

[mon2]

Yes. This may be bad news as this rail is linked to the CPU / PCH = both on the same die. At this time, suggest to inject 0v8 to 1v0 (not higher) onto the same rail you are measuring @ 0v. Then remove the heatsink on the CPU and check who is heating up.

While the CPU / PCH will have a low resistance to ground even if ok but it should not be at 0R. That is a dead short. Perhaps we are lucky and it will be one of the caps you are probing Can only tell with the voltage injection. Keep the voltage at 1v or lower & the highest current your power supply can support. This will make the shorted part heat up and crack under pressure..like a police interrogation.

[thecookie17]

Yes. This may be bad news as this rail is linked to the CPU / PCH = both on the same die. At this time, suggest to inject 0v8 to 1v0 (not higher) onto the same rail you are measuring @ 0v. Then remove the heatsink on the CPU and check who is heating up.

While the CPU / PCH will have a low resistance to ground even if ok but it should not be at 0R. That is a dead short. Perhaps we are lucky and it will be one of the caps you are probing Can only tell with the voltage injection. Keep the voltage at 1v or lower & the highest current your power supply can support. This will make the shorted part heat up and crack under pressure..like a police interrogation.

I did remove L8060 and it shows 0Ω on Pin 2, and the guy over at the other forums said it was likely 99% CPU, should I still bother injecting voltage?
https://boards.rossmanngroup.com/thr...jumping.60117/

I don't have a good lab bench psu right now I'd have to get one but if it'd be worth trying i would do that.

[thecookie17]

Wait.. actually I remembered I picked such a power supply out of the trash once. Seems to work okay, i can dial in 0.8V. It can only supply 2A however; that would be only 1.6 Watts, would that be enough?

[thecookie17]

Okay sorry, I fucked up.. I tried soldering that inductor back on and some capacitor moved and flew away when trying to solder it back, I also don't have the proper tools for microsoldering, just a big ass heatgun. As said I'm doing this for the first time.
I don't know if getting a known working board for around 65€ for this macbook is even worth it (flexgate issue etc..), maybe I should sell it or keep this board to pratice microsoldering on in the future. (After getting proper equipment)
Thank you so much though for your help (and your time).