First of of all big thanks for Fraser and other for sharing their experience with this thermal cam.
I got the 690B variant less than a year ago and that sucker died on me.
I paid about 300 European dollhairs, and it got used 3 times. So it ended up costing 100 Euros for each use.
Lesson learnt again - stay away from chintsy home gamer tools. There is a reason why you never see Uni-Ts used by professionals here in north Europe.
After not using it for several months I tried to turn it on. There was just a brief flash of backlight and then it turned black.
I thought it was just an empty battery and quickly hooked it up to a USB-c charger (for Lenovo laptop).
After charging for a while it remained completely dead. I tried Banggood custormer service, but all I got was a "sorry your crap is out of warranty
"
So I'll have to try my luck repairing it meself.
Next I stumbled on this thread and was able to gut the camera. I used a suction cup and a little heat to remote the plastic screen protector.
Inside visually everything seemed to be ok. No trace of smoke. I went to ebay and ordered some replacement P-channel mosfets.
Battery:
I also checked the internal battery on the terminals and it is dead, 0 Volts. Hmm.
There seems to be a built in protector circuit in the battery under the plastic wrapping, so I went ahead and carefully removed some plastic wrapping on top of the positive and negative strips connecting the cell to the protector circuit and it measured 3.05 Volts, so the cell was not dead after all. I tried to charge the battery with a regular li-ion charger, but it could not detect the battery. I put some small jumper wire to the exposed strips and connected the chareger directly to the cell. I charged the cell to 3.8 volts, and hoped the protector circuit would wake up. The terminals still show 0 Volts. Maybe the protector circuit died.
Booting up:
So the battery was dead, maybe that was the reason for the unit not booting, so next I hooked a lab power to the battery connector on the main PCB and started experimenting.
3.3V:
First I set the lab power to 3.3V (simulating an almost empty battery) and wanted to see if it powers up. Well, partial success. I get now the Uni-t splash screen and initializing gets stucked at 69%. Current draw is about 350 mA. Power button does not work. after couple of tries the boot gets stuck at 70%.
3.6V:
I raise the voltage a little and the unit gets stuck at 70% for a very long time (several minutes) and then goes to 100% and gets stuck. Intresting. I do a power reset a few times and power button does not work. Unit gets stuck at 100%. Maybe I need to raise the voltage more.
4.1V:
Now the boot seem a little faster and on the first try it booted almost up and did not get stuck at 100%. Instead it got stuck on the main camera view screen with "Initializing". Current draw is about 400mA. Power button has now some effect, it switches off the screen, but current draw remains over 300mA, which is not good. I repeat the same a few times. Power cycling seems to be the only way to stop the unit from drawing high current. Maybe I raise the voltage a little.
4.2V:
This would resemble a full battery. This time the unit boots fully up and starts the thermal camera, wohoo! Now also the power button shuts down the unit properly and current draw goes from 400 mA to zero. I notice the date on the screen is from 2022, so RTC battery probably also died.
What happened:
I am suspecting I had an empty battery, then hooked the unit up to a powerful charger and burned something inside. The unit still somehow works, but requires a higher voltage, and would not work unless the battery was fully charged. I am suspecting the unit has a design flaw or a FW bug causing the unit not to always shut down properly, especially with lower supply voltage, and this may then finalize your battery.
I will continue the repair some day when I have time.