and see if it is glowing orange. This is what makes
the high voltage power supply work. If it is glowing then another possible
trouble could be the 1600 volt filter condensers.
* The most common problem is the high voltage for the Geiger or Scintillator tube.
How do I check the high voltage?
On most detectors the high voltage is about 800 volts with the exception that scintillators have 1000 volts. The problem with checking the high voltage is that a regular multimeter has too low resistance and will cause the reading to be low. Without the proper test equipment you can still make a couple of observations to determine the possible problem.
First look for a small glass Neon tube as shown
here and see if it is glowing orange. This is what makes
the high voltage power supply work. If it is glowing then another possible
trouble could be the 1600 volt filter condensers.
If they look like one of these 
they are probably defective from age and should be replaced with a
new ceramic capacitor.
* Another common problem is the Geiger tube.
How can I check it?
Most of the old counters used a 1B85 thin walled aluminum tube.
These tubes would often collapse and look like this 
.
If yours looks like this you need a new one. Also if the tube is the original
one from 1955 it is probably weak and should be tested or
replaced.
*
What about scintillators. In their case it is a little easier to determine
if the crystal is bad. A good crystal will be clear but if it is bad it will
be opaque or yellow like this 
.
If you would like to learn more or have a question, Please contact me at agoshy@e-mtech.com