Max77620 missing 1.1V voltage rail

Hi everybody,
on my Switch the 1.1V from MAX77620 is missing. I desoldered and tested the corresponding inductor and capacitors but they are ok. Now measuring on the blank pads gives me these values:

Before i try to trace the whole voltage rail to find faulty parts:
which components getting the 1.1V?
Just the CPU or others too?

Thanks for your help!

Best regards

Primarily Ram afair, and SoC of course has connections/IO to Ram.

8.7ohm would be very low on this rail. Check you other rails too (don’t bother with diode mode, use resistance) to make sure there isn’t another issue causing it to be dragged down. Check SYS rail also. Though, that being said, I’d doubly make sure your taking your readings correctly as afaict, your reading 8.7ohm on one side of the inductor relative to ground and 6.4 meg on the other side (?), which doesn’t make sense (provided the inductor isn’t damaged or I’m misinterpreting your image), so I’d double check that :slight_smile:

Hi Severence,

first of all i want to thank you for your help!
Like said i desoldered the inductor and the two capacitors because my first suggestion was that they are maybe faulty.
Nevertheless, i double and triple checked my measurements again and got the same results.

Best regards

Ah, I see, yeah makes sense now with the inductor removed. Future reference, if you remove the inductor first then you can see that the fault is further downstream (as in your case) and can rule out the PMIC, which saves you the hassle of removing etc :slight_smile:

There is a fair number of caps on this rail but I rarely ever get failed caps in these sort of instances, but maybe you’ll get lucky and find it’s one of them, unfortunately I’m leaning more towards it being your Ram or SoC being at fault but I’d still check your other rails first incase something else is causing this rail to be dragged low (which is also semi common)

Any signs of rework at SoC/Ram?

Also what you could do to potentially narrow this down further is, find a consistent ground point and maintain it (USB copper through hole pads are a good choice) and record the reading in resistance you get on the “shorted” side of the inductor pad (the approx 8.7ohm one) note the reading, then find the cap/s which run along side the Ram IC which are also on this rail and note the reading, there is also cap/s directly on the SoC wafer which are also on this rail too if I remember correctly so do the same there. Hopefully your meter has the resolution but if you get 8.7 ohm at the PMIC inductor, and 8.5 ohms at the Ram caps, and 8.6 ohm on the SoC caps (all just for example) then you could safely say it’s more likely to be the Ram at fault.

Though, as I say I’d still check your other rails first.