5V output seems low - damaged regulator?

Th0mpy

Just noticed that one of my Duet 3 6HC boards started having weird issues, primarily related to the SBC.

Within the Raspberry Pi I noted that I started to get "undervoltage warnings" which caused the SBC to throttle the CPU and in turn made the Duet interface laggy. This is a Raspberry Pi 4, and I do power the SBC from the Duet.

I did recently replace the 24v PSU since my original one had a fan that died. The new one was slightly lower current. Otherwise, nothing else has changed and this was working fine maybe a month ago.

Trying to narrow down what was happening I unhooked the Pi and checked the 5V and was coming up with 4.88V. Taking it further, disconnected everything from the outputs/inputs and it did increase to 4.93 (higher, but still less than 5V).

What more can I check? This does seem to me that the 5V regulator is bad or failing.

jay_s_uk

@th0mpy its not advised to run a pi 4 from the duet 3. best to get an independent PSU for it

Th0mpy

@jay_s_uk I agree, and I finally read that just last night I have a new PSU coming to do just that. That said, I'd still like to make sure the board is good once that's done.

droftarts

@th0mpy See https://docs.duet3d.com/Duet3D_hardware/Duet_3_family/Duet_3_Mainboard_6HC_Hardware_Overview#h-5v

Previous versions of the Duet 3 Mainboard 6HC allowed for the Duet to power the SBC, or the SBC to power the Duet. More modern SBCs (e.g. RPi 4) needs too much 5V power, especially with a screen, to make it sensible to supply from the Duet. Similarly the spare 5V power budget on the SBC may not be sufficient for the Duet. In addition some SBCs require >5V on the 5V rail to not give an under voltage warning.

(re 6HC board revision v1.0.1a, but also relevant for older boards.)

Ian

jay_s_uk

@th0mpy it should be fine. the SBC does lead to some drop and pi's prefer a 5v supply closer to 5.2v
do you run any other 3.3v or 5v things from the duet?

Th0mpy

@jay_s_uk I do. I am running it stand-alone now and everything seems fine, just the voltage on the 5V rail is a bit low.