MacBook logic board 820–01949 repair help needed please

[boosti45]

I have a 2020 MacBook Pro touch bar 13 inch with the board 820–01949 that I'm currently working on that is my personal computer and long story short quit working got 5 V and no amps found out the computer was in DFU mode and I finally got it to go through and get on, and it would make it about halfway through, and then it would freeze while reviving so I would end up turning it off and starting over and on the third or fourth attempt I decided just to let it sit there and be frozen and see if it eventually finished and I came back like 15 minutes later and the computer was off and so I ended up looking at it under a microscope after taking it apart and then I used a thermal camera and found chip U6903 glowing instantly upon injecting voltage after verifying that I was able to do so through another individual and before I got to 2 V that chip was glowing red under the thermal camera so I then removed it from the board and I ordered a replacement. Then installed it and put fuse back on F7000 and now the computer when you plug it in once again is only pulling 5.172V and bounces between .028A and .024A and .032A on all 4 ports so this time, I figured I would ask someone knowledgeable in this type of stuff to please essentially walk me through what I need to test and what's the best way to go about finding out what the issue is? And I attempted several times to see if I could get DFU mowed up, but that had no success go around so any help or information Will be greatly appreciated!

[mon2]

With no power, meter in resistance mode, what is the resistance in ohms (not diode) to ground of F7000? Measure both sides of this fuse.

[boosti45]

3.8 ohms

[boosti45]

It just keeps climbing it was at 10 mega ohms when I stopped tracking because I did locate a short directly after posting my previous reply and fixed that and now it's no longer 3.8 ohms but 10 Or more mega ohms and I'm getting 12.35 V on PPbus_G3H and I know that's indicative of a non-booted T2 corruption issue meaning it should be in DFU mode but my question is if that's the case would it still be pulling only 5 V or 20 V?

[mon2]

Measure the voltage to ground of the battery connector. The shared smbus lines are used to bump the ppbus_g3h voltage which is currently lower than normal.

[boosti45]

Where would I measure that at exactly? And sorry I’m new to this Type of troubleshooting, lol

[mon2]

At battery flex connector J6951.

Carefully measure the voltage to ground:

black meter probe to ground (metal shield is ok).
Red meter probe to point to test.

Interested mainly on the SMBUS lines:

I2C_PWR_SCL
I2C_PWR_SDA

If the process is not practical to perform, remove all power. Meter in resistance mode.

Proceed with the same test to confirm if these SMBUS lines are shorted or not. We are checking the resistance in ohms with NO power to the board.

Be sure your meter probes are fine tipped enough so they do not short any adjoining pads.

[boosti45]

got 0v with power connected on lines 2 and 3 which is smbus_3v3_batt_scl and smbus_3v3_batt_sda and without power and in resistance mode I got 4.647 K/ohms and 4.644 K/ohms on those same two lines at the connector u said to use to check

[mon2]

No short here but means that you are missing the pull-up voltage rail PP3V3_G3H_RTC that is required by these open-drain pins (SCL/SDA).

Measure the voltage to ground of PP3V3_G3H_RTC to confirm if this rail is present or not. If not present, power down and check the resistance to ground of PP3V3_G3H_RTC. If this rail is not present then it is either shorted OR not being enabled.

Enable pin = CHGR_EN_MVR and CHGR_EN_MVR_R. Confirm if there is an enable voltage on both sides of R6907.

[boosti45]

4.6 ohms on pp3v3_g3h_rtc and 5 volts on both sides of r6907

[mon2]

So this rail is being enabled.

The rail pp3v3_g3h_rtc is shorted.

Would you have an adjustable power supply? If yes, that power supply dialed to 1 volt (recommended) at 2A-5A current, injected onto the same rail should cause the shorted part to heat up. You can use a thermal camera or IPA (Costco pharmacy alcohol) poured over the suspects will cause the IPA to evaporate with the heat.

[boosti45]

Could there be a short in between some of the pans on the chip u6903 that I replaced that could be causing the missing pp3v3_g3h_rtc cause I'm fairly positive pin 4 of U6903 which is pp3v3_g3h_rtc_reg_r is the same exact 4.6 ohms if I am in fact touching underneath the corner where I think I am of that chip lol if that makes sense

[boosti45]

Yes, I have thermal camera and I have a benchtop power supply if that's what you're referring to That's adjustable which is how I injected voltage the first time to find out that u6903 was bad before I replaced it

[boosti45]

Where should I choose to inject voltage at? And is it possible that a chip I purchased brand new could be bad if it's got something to do with the shorted line we are talking about?

[mon2]

Post a few close up pics of the reworked IC.

[boosti45]

OK while trying to take photos just now for you I came across a chip labeled as U8501 that is burnt and very clearly bad like no denying it's visibly destroyed.... And it's on the opposite side of the board and according to the schematic has three connections I believe it said to pp3v3_g3h_rtc so if I had to guess that's where the short is coming from so can I order that part from the same website that I got the ic from? which was digi-key....

[mon2]

U8501 = Silego SLG5AP1443V

Suggest to order it from Mobile Sentrix or Aliexpress. Could not find it on Digikey.

SMD Controller IC Replacement For MacBooks (Silego,SLG5AP1443V / SLG5AP1443VT / SLG5AP1443VTR / 5AP1443 F5A FRW Fxx ,U8680 / U8670 / U8650 / U4190, SYDFN-8L) (mobilesentrix.com)

[boosti45]

Yup I was just putting a picture of what the schematic said, which is exactly what you just attach the photo of because I was having trouble finding it on digikey myself lol so I will order that and get it swapped over and report back once it is in place and make sure that the short is gone on that line and either way, I will let you know and I truly appreciate you taking the time to walk me through figuring this out. It’s very very much so appreciated

[mon2]

Np. Glad to have helped. If you have not ordered in the past from Mobile Sentrix, they work only with repair shops and not individuals. Setup an account of work with someone who does. They have very good service with quality parts but limited on overall selection. Kind of like Aliexpress but for North America - we have a local office of theirs here in Canada. Do continue to update this thread for future readers but it appears you are close to finishing this repair. The damaged part is a small sized load switch which acts like a solid state relay with a bit of decay time to prevent sudden current surges which are not desirable. Only when the enable signal is active, will the load receive the power rail voltage.

[boosti45]

U4920 is also bad ...... what's its purpose and where can I order that one?