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I've done a PMIC replacement once on Rasp pi 3B+ and managed to get it working again. This is the second time I've done a PMIC replacement.

The symptoms are exactly the same, PWR LED on, 3v3 and 1v8 shorted to ground. So I used my already-in-stock MXL7704-R3 to do a PMIC replacement. After replacement, I inserted a working SD card tested on another rasp pi. ACT LED turned on with a 4 slow blink and 7 fast blink sequence, indicating a power failure type B. Unfortunately I can't seem to find anything about power failure type B. Any info on this will be appreciated.

After that, I unplugged the rasp pi and plugged it back in. The 3v3 line is still normal. however, there's no voltage on 1v8. Tested for short and no short on 1v8, so there is no problem with the PMIC.

I want to know what's the cause of this problem as I managed to do a PMIC replacement on another 3B+ with the exact same batch of PMIC.

does it have something to do with the programming of the PMIC?

something to do with the SoC and PMIC I2C communication?

Is it possible to fix it by myself or is it a dead end?

edit: Here are pictures of the rasp pi,

My Rasp pi original rasp pi

I noticed that there're some missing passive components (3 of them). Are these passive components critical? If so what passive components go there? I'm having a difficult time finding out what components that should go there.

https://datasheets.raspberrypi.com/rpi3/raspberry-pi-3-b-plus-reduced-schematics.pdf

Missing Passive Components

Is the missing passive components the culprit? Any info on what components go there would be valuable. I still want to continue fixing this rasp pi to practice my skills.

1 Answer 1

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I've done a PMIC replacement once on Rasp pi 3B+ and managed to get it working again.

I may be missing something, but AFAIK you would have had to re-write the I2C registers on your replacement PMIC to get it to work with the RPi. Did you do that? If so, you can skip the balance of this answer.

AIUI, the PMIC used on RPi's is different than the commercially-available parts sold as MXL7704/XR77004. The difference is some register programming that pertains to the I2C on-chip interface that is applied to the part to make it work with RPi. And so, replication of this register programming raises the bar for a successful replacement of the PMIC.

I've found two (2) reports that claimed this was done successfully:

  1. An RPi forum post titled "RaspberryPi 4 MXL7704-R4 PMIC replacement and repair"

  2. A post on Hackaday titled "Dead Raspberry Pi Boards, PMICs, And New Hope". One of the replies to this post linked to this YouTube video that seems to claim a repair was successfully accomplished. However, the video soundtrack is in Romanian, so it's a bit tough to know exactly what happened here :) I saw nothing related to the programming of the PMIC, so maybe all that's offered here is some info on de-soldering and re-soldering the chip on the board.

While the soldering techniques in #2 were fascinating, only #1 gave any information on programming the PMIC registers. But the Hackaday article also acknowledged that the forum post was lacking a crucial step, and that the procedure had not, so far, been replicated.

  1. I found a third report in this wiki. The article offers some information on suitable replacement parts for obsolete/discontinued PMIC chips, which might be useful. It also has some breakdown on the register values for Pi3 vs Pi4 - again, potentially useful stuff.

So - that's the scoop. Hopefully, we'll hear from you again, and learn how you accomplished your repair.

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