Smart Tweezers ST5L - won't turn on

[Howardlong]

Folks

I've had a pair of these Smart Tweezers for a couple of years now, but I've not used them recently because they won't turn on. I already had it apart some months ago, and while I was trying to debug them they suddenly started working again for a few weeks, then they stopped working.

When I plug them into a USB port, they take 7mA, but that's it. There's no indication that the battery is charging.

So before I reinvent the wheel, has anyone else encountered this behaviour, and if so did you manage to fix it?

[floobydust]

I would take out the battery and see if it's voltage is OK. Or you wrecked something when you were in there 

Smart Tweezers (Advance Devices Inc.) are very good answering technical questions, hit them up.

I saw this with a battery too far gone for it to initiate charging.

I ended up sending mine back for the firmware update regarding reading MLCC capacitors.

[Howardlong]

Well, this is what this forum's all about! That's exactly what happened, the cell was at such a low voltage it refused to charge at all. Possibly a design feature that may well be fixed in other models, I don't know).

I took it apaaaart, four T6 self tapping screws, and measured the battery voltage, 200mV, so nowhere near enough. I set the lab PSU to 3.7V and current limited 70mA, and poked the battery terminals on the PCB connector. A few seconds of charge and she'd sprung into life. Charging current is 51mA.

Underneath there's a single cell LiPo 180mAh, you need to take off two more T6 screws and two Phillps head to access it, but it's not necessary for this process unless you want to change the battery.