I bought one of those cheap $40 GM radiation detectors and when it arrived it didn't detect sh1t!
On power on it initially starts displaying a fixed 0.16uSv value that slowly over a minute trends to 0 and stays there even in the presence of radiation.
It's not worth the time and effort to me to return it and ask for a replacement plus I really wanted to take it apart right now instead of waiting.
If anything I'll buy a different type next time, if I can't fix this.
Removing the 4 screws detaches the back and we initially see a 1Ah marked LiPo and the J302 GM tube on a PCB with SMD components.
Removing the battery and GM tube reveals the rest of the PCB with a HK32F030C8T6 micro made out of pure chinesium. A TP4056 LiPo charger can also be seen next to the beeper.
The unpopulated components might be an EM field detector (these gadgets can be bought as a combined Nuclear + EM radiation detectors)
The other side of the PCB doesn't have much except the buttons, an LED and a LCD connector.
There seems to be space for a bluetooth controller which is not fitted.
The LCD is a Z180SN019 1.8 inch TFT based on a ST7735S controller with SPI.
I believe the reason it's not detecting anything is because the voltage across the tube is too low.
The J302 GM tube needs a nominal 400VDC supply but I can only measure about 250VDC across it (with a Fluke 75III 10M input impedance).
I'm not even sure what topology they have used for the voltage multiplier, I expected a typical Cockroft-Walton multiplier but tracing the circuit I end up with this
Does anyone even recognize this topology? I haven't seen it before.