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Oh, I see. I looked up the datasheet on my LM555CN; it doesn't say CMOS anywhere, so I assume it is not. Is that the part you would recommend I replace next?

I found a drawer of 555 timers, so I tried replacing U1. After doing that, the detector didn't seem to pick up any ambient radiation, but it did click when I touched J2 and J1 and when I tested the voltage between pin 3 of J6 and TP1. I then tried measuring TP2. I got erratic readings on my multimet...

Thanks for getting back with me so quickly. I replaced Q3 as you suggested, but not much changed. The only major differences I found were the measurements on pin 4 of U1: With the IC in: 2.215v IC out: 2.392v U1 sockets 3 and 8 shorted, pin 4: 0.041 Still does not whine on startup or respond to the ...

Hello MightyOhm, I built one of your Geiger Counter kits and it worked fine for a while, but then it just stopped. The batteries seemed low (2.6v together), so I hooked the circuit up to my power supply at 3.00v. (I tried to be careful with the power supply, but the only way that I can think of that...