Symptom: No audio.  It was reported that one day it was working fine, then it didn’t.

Checked the muting relay; okay.  Checked the amp by playing a selection that had no record in it (to un-mute the amp) and injected an audio signal from an iPod.  The amp worked fine.  That left the wiring from the amp to the cartridge or the cartridge itself as the culprit.

The owner had re-soldered the connections to the cartridge socket, thinking that something had gone wrong there.  If I understood correctly, the socket was unsoldered when he purchased the jukebox, so he or someone else had soldered the connections originally.  So there is some question as to whether the connections have been made properly.  The cartridge is a stereo Pickering 340-D and I could not find any documentation as to the connections.  Assuming this is a ceramic cartridge based on the age of the jukebox, I should have easily been able to see some kind of signal on the oscilloscope as I touched the needle.  I checked every possible connection arrangement.  As a double check, we connected the cartridge directly to the amp using alligator clips, again trying every possible combination.  The only conclusion was that the cartridge was bad.

In the past, I’ve seen some old crystal cartridges stop working.  I’ve also seen a stereo ceramic stop working on a friend’s Grundig.  Bad cartridges are nothing new, but it’s still surprising whenever I come across one.  What’s interesting in both the case of the Grundig and the jukebox is that both channels stop working. I’d think that only one channel would fail, but I don’t know what is failing inside the cartridge.  One of these days I’ll have to open one up and see why.  Maybe they can be repaired, although I’ve never heard of it.

This jukebox is not fixed yet.  The owner is going to obtain another cartridge.  Unfortunately cartridges for jukeboxes are becoming extremely rare.  I will update this post when the owner obtains another cartridge.

Something that doesn’t add up on the Jet:  The cartridge is stereo, the wiring to the amp is stereo, the schematic claims the amp is stereo (but I didn’t actually verify that), and the wiring from the amp to the speakers is stereo.  Inside the amp, right at the input it is factory wired to short both channels together.  Maybe Seeburg had two versions of amps.  Stereo was in its infancy in those days.

Update 4/4/2012: The owner obtained a new cartridge and it’s now working!

Location: Loveland, Colorado