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My family and I built the geiger counter a few weeks ago, and it worked fine then, but today it stopped working. No multimeter is currently available, but one may be in the future. The batteries are fine, and there is a beep when I shorted across the ends of the tube. However, it detects little or no background radiation and the variable resistor has no effect. I didn't hear a whine when I turned it on, but I never have before.

Do you have a test source you can use to verify that the counter is not responding?
When measuring background radiation, how many clicks do you count in a minute? Typical levels are around 10-30CPM.

One so far (after a few minutes). We don't have a test source, but we were getting background before and it all stopped. I recently heard the whine when it turned on (for the first time). We just checked the solder, and there were no real problems. As I said, it still beeps when there is a contact across the clips at the end of the tube. Removing the case made no difference.

Where do you have the variable resistor set? Does changing it have any effect?
You may have a bad Geiger tube. If you can check the HV with a multimeter that would help isolate the problem.

Any updates? Are you still having problems?