Macbook a1707 - 3 ports cycling and 1 stuck on 5v

[vanromic]

Hello! I'm trying to resuscitate a Macbook that the local tech gave up on. I have the board view and schematic and have the main board out of the case.

Of the 4 usb-c ports, 3 cycle at 5V - they all go up to about 1.5A, then seem to switch off, back to 5V 0A, up to 1.5A, and off again. The cycle lasts a few seconds - maybe 3s.

The 4th port doesn't cycle and draws ~0.5A at 5V consistently. It seems it's the port linked to U3100 - it's on that side of the board and is the port closest to the battery and the CD3215C00 chips.

I've read that the CD3215s are configured as master-slave and I'm guessing that the 3 that are cycling are somehow failing to initialize and that U3100 might be the problem, or the problem is in the sub-circuit for that port.

If anyone out there is familiar with this board and / or this particular failure mode and could give me some pointers in terms of troubleshooting before I rush out and by a new CD3215C00, I'd be grateful - thanks!

[mon2]

Test the voltage to ground of each such cd3215's LDO power rail. Check the schematics to locate the power rail for each part and confirm they are present. Post the list of measurements for each.

Each cd3215 must be working to allow for the 20v power delivery contract negotiation.

reference:
https://logi.wiki/index.php/CD3215_Bootup_Sequence

With no power, meter in resistance mode, measure the resistance to ground of each inductor. Usually are grey in color. Post each resistance in ohms. Checking for shorted parts on that local power rail. Often a shorted capacitor.

What is the voltage to ground of ppbus_g3h?

[vanromic]

PP3V3_UPC_XB_LDO is 3.24V for U3100, 0.37V for UB300, 0.26V for UB400, 0V for U3200.

PP3V3_G3H is 0 or close to it on all four cd3215s. From watching too many Louis Rossmann vids, this is a bad thing...

Still working my way through the inductors - there are many and some are tiny.

Unfortunately I need to leave this until the weekend - I'll post L values then. Thanks for your help!!

[mon2]

Ok, some issues there. With no power, measure the resistance to ground of each power rail that is not matching the schematic values.

The requested rail was PPBUS_G3H.

Measure the voltage to ground of this critical power rail. If it is not within specifications, remove all power and measure the resistance to ground of this power rail.

[reformatt]

5V @ 1.5 amps seems way too high. Make sure you have battery disconnected during these kinds of tests.

Check resistance to ground for the PPBUS_G3H and PP3V3_G3H rails. As the board has been worked on by someone else, there can also be an introduced fault so recheck all board rework first.

[Aliencomputres]

change both CD3215C00 !

[vanromic]

On looking over this logic board in a little more detail, I've noticed that Q3100, a dual mosfet FDPC4044 is missing and must have removed by the tech who worked on the board.

I don't want to waste the time of those on this forum and am first going to see if I can get hold of this chap to find out exactly what work he did, so that I can try to get the board back to at least having all the components it needs. I noticed an inductor missing as well, but am not sure whether he removed it, or if the board was fabricated without it.

I feel it's best to pause this thread for now until the board is in a better state. Thanks to all who have tried to help so far!!