I recently acquired a Victoreen CDV-700 Geiger Couter from a local surplus store. The unit appeared to be in good condition, however, upon testing it I found that while it does detect radiation sources, its meter is not registering anything.
I tested the meter and found that the gauge itself is actually working and that the problem was somewhere in the circuit board. Luckily the good folks at Victoreen Instruments were kind enough to include the following diagram inside the box:
I will have to test the components to find if there is a short or a bad part and then see if it is fixable. On the other hand, it was manufactured in the early 70’s, so it may be hard to find replacement parts if anything is in fact bad.