I have a small, handheld geiger counter made by a firm called RDX Nuclear (model is DX-1). Unfortunately, a much younger family member than I decided to try putting a 9V battery in it, but he put it in the wrong way before I could intercept him. Now, when the activation button is pressed, all I'm getting is a constant tone. Within the tone, I can hear individual clicking as if it is still taking counts, but that's it. Also, the indication needle is pegged. Here is an image of the top of the circuit board:
Unfortunately, I've never seen a schematic of this unit on the web even though it seems to be sold all over the place. Contacting RDX, all they want to do is replace that tiny board... for $120. So, if you hooked it up backwards, what would you check first? I did check the diodes and they all seem fine.