Macbook Pro A1708 820-00840 no power

[reformatt]

12 ohms on PP3V3_G3H is not looking promising. Does appear as if D6905 and U6990 both been zapped by something. You can remove R6999 to isolate which side you are seeing this low ohms measurement. There are many bits of silicon on that power rail, like the SMC and CD3215's.

The only way I can see voltage on U6990/2 with D6905 removed is if U6990 is shorted internally and there is voltage coming back in via PP3V3_G3H. The only other rail active at this point is PPBUS_G3H so I'd be looking at components where both of these power rails are present.

I'll be honest, my gut feel is I think your chances of repairing this board are quite slim at this point. It's hard to know without an understanding of what your other half did to create this level of damage.

[khanc0724]

1-3 is ok
2-3 is not ok if you have red on pin # 2; black on pin #3. You should have a similar measurement of .22v like 1-3.

This diode is defective.

Carefully flux and remove resistor @ R6999. This action will isolate the producer and consumer sides of the power supply. Then measure the resistance again on L6995 - either side. Do you still see a low resistance of 11R8 ohms to ground? If yes, the issue is on the producer (regulator) side of the circuit. If not, the short is on the consumer (downstream / load) side of the circuit.

Confirm the details.

Removed R6999. When checking resistance on L6995 I now get OL on both side.

[khanc0724]

12 ohms on PP3V3_G3H is not looking promising. Does appear as if D6905 and U6990 both been zapped by something. You can remove R6999 to isolate which side you are seeing this low ohms measurement. There are many bits of silicon on that power rail, like the SMC and CD3215's.

The only way I can see voltage on U6990/2 with D6905 removed is if U6990 is shorted internally and there is voltage coming back in via PP3V3_G3H. The only other rail active at this point is PPBUS_G3H so I'd be looking at components where both of these power rails are present.

I'll be honest, my gut feel is I think your chances of repairing this board are quite slim at this point. It's hard to know without an understanding of what your other half did to create this level of damage.

Already confirmed D6905 is bad. Just removed R6999 and no short to ground on L6995 and OL for resistance on both pins. With R6999 removed, can I or should I apply 5V and check the pins again?

[khanc0724]

12 ohms on PP3V3_G3H is not looking promising. Does appear as if D6905 and U6990 both been zapped by something. You can remove R6999 to isolate which side you are seeing this low ohms measurement. There are many bits of silicon on that power rail, like the SMC and CD3215's.

The only way I can see voltage on U6990/2 with D6905 removed is if U6990 is shorted internally and there is voltage coming back in via PP3V3_G3H. The only other rail active at this point is PPBUS_G3H so I'd be looking at components where both of these power rails are present.

I'll be honest, my gut feel is I think your chances of repairing this board are quite slim at this point. It's hard to know without an understanding of what your other half did to create this level of damage.

I see what you mean now. Since the fault seems to be on the consumer side, there are too many components to isolate and track down the short. I think I might have reached an end with this one. Seems like a new logic board will be a lot less of a headache at this point :-D

[reformatt]

I see what you mean now. Since the fault seems to be on the consumer side, there are too many components to isolate and track down the short. I think I might have reached an end with this one. Seems like a new logic board will be a lot less of a headache at this point :-D

It may be multiple components if there was an overvoltage, not just one. I did have a 2017 Macbook Air board I had to write off because one of the 3.42V supply feedback voltage divider resistors had changed in value and resulted in the regulator outputting 6V instead of 3.42V. Basically killed everything on that rail.....I replaced the SMC, clock chip etc only to find the RTC section of the PCH shorted.

[mon2]

IMHO, attempt a few more checks before throwing in the towel. Suggest to replace this regulator @ U6990.

This is the adjustable Vout version (as used on the logic board):

https://www.digikey.ca/en/products/d...ETBC-T/5880839

Leave R6999 disconnected and off the board. Then power up again.

Test if the Vin pin #2 has a voltage like the defective part.

Stuff a fresh known good dual diode @ D6905. Power up again. What voltage do you now measure @ L6995 pin # 2 (without R6999)? Is it stable and matching the schematic values?

If yes, the bias resistors on this circuit are ok.

Next need to test the shorted part that can follow.

[mon2]

Suggest to also purchase the resistors on this regulator to rebuild the circuit if needed. Low cost from Digikey. 1% tolerance.

[khanc0724]

Suggest to also purchase the resistors on this regulator to rebuild the circuit if needed. Low cost from Digikey. 1% tolerance.

Did some more desoldering. I removed U6990. I measured the voltage at U7000 following the boot sequence and noticed that it was 4.9v up until it left from EN_VR1 to R6999. At R6999 it dropped from 4.9v to 1.5v. I removed R6999 and tested voltage at the the pad and got 4.9v. I'm still getting .5v at pad 3 of D6905, not sure if that's relevant. I don't have any new components yet so I can't install and re-check. I am also still getting 12 ohms to ground on pad 2 and now 160 ohms to ground on pin 1.

[reformatt]

Did some more desoldering. I removed U6990. I measured the voltage at U7000 following the boot sequence and noticed that it was 4.9v up until it left from EN_VR1 to R6999. At R6999 it dropped from 4.9v to 1.5v. I removed R6999 and tested voltage at the the pad and got 4.9v. I'm still getting .5v at pad 3 of D6905, not sure if that's relevant. I don't have any new components yet so I can't install and re-check. I am also still getting 12 ohms to ground on pad 2 and now 160 ohms to ground on pin 1.

Not really following here. R6999 is on the output of the converter, not sure how you relate that to the enable signal on the input? BTW, the enable (PM_EN_PP3V3_G3H) is simply a logic level, not a power source.

With U6990/R6999 removed, you should have 0V on PP3V3_G3H.

[khanc0724]

Not really following here. R6999 is on the output of the converter, not sure how you relate that to the enable signal on the input? BTW, the enable (PM_EN_PP3V3_G3H) is simply a logic level, not a power source.

With U6990/R6999 removed, you should have 0V on PP3V3_G3H.

My mistake, correction the EN_VR1 to R6991 not R6999. The voltage drop was at R6991 but when I removed it and tested voltage at pad 2 of R6991 it went back up to 4.9v.

[reformatt]

The measurements you are reporting make no sense if U6990 and D6905 are removed off the board.

What voltage if any do you have on PP3V3_G3H when power is applied, and R6999 is removed as well?

[khanc0724]

The measurements you are reporting make no sense if U6990 and D6905 are removed off the board.

What voltage if any do you have on PP3V3_G3H when power is applied, and R6999 is removed as well?

PP3V3_G3H is 0v with power applied. The 4.9v i'm referring to is at R6991 with it removed. When it was still on the board I would only get 1.5V at R6991. Since it's a 0 ohm resistor i'm guessing it was drawing the voltage down.