[MrFixr55]

Hi Pete,

Some more info that may be useful:

The Phono motor runs on 115V (OK, 120 now).  You can connect the motor circuit directly to a cord and connect to house current, but to help protect you from shock in case you come in contact with a bare connection, use an isolation transformer.  The M20 Manual Ron supplied will be helpful in figuring out the connections.

First off, check the Audio Input jack on the radio by connecting the output of a CD, MP3, etc. between Pin 1 or 3 (chassis ground) and pin 2 (the audio in.  Set the radio to phono.  The CD  / MP3 should play loud and proud.  If not, troubleshoot.  If the sound is good, then work your way back and inject the signal through the "STD  / 45" Switch and finally the tone arm.  If all this is good, then the cartridge is dead.  The cartridge can be checked by connecting a DVM across the terminals and scratch the needle.  Try both AC and DC.  An output of about 0.5v or more should be produced.  If no voltage is produced, then the cartridge is dead.  I wouldn't bother trying to measure resistance, there is no specification for that. 

Note that the cartridge is in series with a 0.01 uF Cap.  This is likely because the changer was used with several different radios or radio / TVs including some "Hot Chassis" (transformerless) models and the capacitor provided a modicum of safety.  This cap like all caps in the radio should be replaced, as they are 70 years old.