I have a device which doesn't turn on normally when you press the power button like it did before. You have to keep holding it down for it to remain on. As soon as you let go, it turns back off.
In troubleshooting so far I've ruled out some of the simpler things like power supply issues, button seating/placement, loose connectors, etc.
My device happens to be an Alesis DMLite drum machine, but I'm hoping this will have broader applications than just my specific situation. I've seen this happen with other devices before. I know this site isn't supposed to be about consumer electronics but I want to make this relevant by trying to learn more about how this circuit actually works.
So the buttons seem to be pretty simple. They are basically just pieces of rubber seated ontop of a few pads on the PCB.
Here is a picture of the front panel:
And the back of the buttons:
And some pictures of the boards (first one is where the buttons connect):
I followed the traces for the power button and one of them ended up connecting to R103, and R104 (both on lower terminal shown in the picture):
It's hard to find where the other end of the switch connects since the traces/vias aren't visible the whole way through. I was poking around with a continuity meter but haven't been able to find where it goes. But neither trace connects to ground.
On the back of that PCB it's a bit easier to trace the signal. Haven't been able to find a datasheet for the SOTs.
So this is what I've been able to trace out so far (lots of guesses esp. on pinout here). I've tried to put in some values based on rough in circuit measurements.
I'm curious if this resembles a common circuit that one of you may recognize. I'm not familiar with this method of switching power. Can anyone shed some light on what this circuit might be doing and how it might malfunction and exhibit these symptoms?