@ChrisP said in Undervolts on Pi:
Looking at the schematic and @dc42's comment, I don't think it is the diodes since the regulator feedback is taken after these.
I've just tried starting my system up from cold with nothing attached to the Pi (other than the D3, clearly) and I didn't get power warnings at all (can be observed by either the Pi's red power LED staying lit or looking at the journal logs).
It may be right on the edge... I do get warnings in the above config. Pi 4B+ 4Gig.
As soon as I plugged the LCD in, I begin getting occasional under-voltage warnings that tend to last for ~6 seconds before the voltage shows as normalised again.
I probably should look at the logs more carefully. Eyeball doesn't see any change when I plug in my 7" LCD... but the Mark 1 eye has its limits. I'll do some math, and see if there is more influence than I think.
If I then open a chrome tab on the Pi with DWC then the it's under-voltage warning is on pretty much permanently with only the occasional flick off - not long enough to register as normalised in the journal logs.
Interesting. I'm letting the Chrome/DWC autostart. So my "nothing attached" baseline has this running. Hmmm....