Switch turns immediately off after plugging charger

Nintendo Questions Nintendo Switch
1

Hello there,

My switch had a shorted BQ and a blown usb fuse. I replaced them and now turns on correctly. However, if I plug a USB cable it turns off immediately. I measured and it correctly negotiates 15V (I assume the PI3USB must be working?) but doesnt seem to pull any current since it doesnt charge. Doesnt matter if I plug it while off, no charge.

What could be the issue? Should i suspect the BQ? Seems like it should be ok since it is new, but who knows… The fuse did not blow again and this turnoff issue is 100% reproducible every time I plug it. I aslo tried plugging it to a 5V usb source and it doesnt turn off but doesnt charge.

A bit of backstory: found the device off one day. Wouldn’t charge nor turn on. Found a dead battery (0V) and burnt usb fuse. A new battery showed that BQ would heat up like crazy, so it was shorted. Replaced them and now stuck in this situaton. Im tenpted to replace the MT and PI3USB…

Thanks!

2

Did you find the culprit in the end?

3

I resoldered again and it doesnt turn off now, but doesnt charge.
Hekate Nyx UI shows that the battery is “hot” and that’s probably why.
I suspect the gauge IC might be identifying the battery as hot or most likely the connection between the gauge IC and the BQ is borked. (The battery thermristor voltage is fine)
I found a few nice schematics (and recently hackaday dot com/2024/02/20/mapping-the-nintendo-switch-pcb/) but I haven’t spent much time since then.
WIll give it another shot in the next days, fingers crossed! (as you can see I donot use it much these days)

4

By which you mean only BQ ?