1965 Zenith MT1960 Console Stereo Issues

[vortalexfan]

Hello everyone, I was just given over the weekend by my uncle a 1965 Zenith AM-FM Stereo Console model MT1960 that used to belong to the mother of one of his friends he used to go to school with that he still runs around with and she had just recently passed away at the age of 93 and she took pretty good care of the stuff she had.

So far I have changed out the filter capacitors that were bad, and replaced the 12AX7 tube that was in the amplifier because it had a dead section and was causing only one channel to function in the radio.

There is another bizarre issue that this stereo has that I haven't been able to track down yet and that is that when you turn the radio to either FM or AM mode the radio shuts off completely but when its either in Phono mode or FM AFC mode the radio works as it should and I was wondering what would cause the mode/power switch to not power on the unit in AM or FM mode but allow it to power on in FM AFC or Phono Mode?

This is an all tube unit that uses the really weird 19v tubes in the tuner section, like the 19EA8 and a 19GQ7 tube the rest of the tubes in the tuner are normal 12v tubes like the 12BA6 12BE6 and 12AU6 and 12DT8, I checked all of the tubes in the tuner section and all of the tubes checked good yet except the 19GQ7 and one of the 12BA6s.

I was wondering if anyone had any experience with these late Zenith tube console stereos and some of the issues they can have.

[damen]

The power switching in this set is done with the wafer sections of the function switch instead of separate "snap" switches mounted to it. Look for burned or damaged wafer contacts connected to the brown, yellow, white,and orange wires connected to the switch (usually these are thicker wires than others in the set).

[Electronic M]

If it kills all power to the set and you're having a hard time tracing it dim the room lights and watch for arcing in the wafer switch when you switch between the modes it's on and off in.

[vortalexfan]

Alright thanks I will give those a try.

This unit is definitely not the easiest to get the chassis out of the cabinet because of how they mounted it in there, they used 3 nuts to mount the chassis to the cabinet for the amplifier/power supply chassis, and the first two nuts are fairly easy to get to the 3rd one though is a PIA to get to because its located between the two tone control pots and its hard to get a socket and ratchet in there without buggering anything up.

The tuner chassis on the other hand I can't see where the mounting nuts are on it because its located partially behind a piece of wood supporting the cabinet and it impedes my line of sight to it, just to check the tubes I had to crane my neck every odd way to see the tube sockets to reinstall the tubes after I checked them.

Definitely not the most serviceable friendly chassis.

As for the "power switch" wafers when I turn it to the functional positions (the FM AFC and Phono positions) I hear a popping noise similar to the "relay click" you hear in the old Pioneer or Sansui stereo receivers from the 1970s and then the tubes start warming up and then I get my audio about 30 seconds later, and when I switch from the functional positions to the non-functional positions (going from FM-AFC to FM) the audio dies out right away with the gradual audio fade out of the capacitors discharging, and there isn't any popping noises when it does that.

[vortalexfan]

UPDATE: I was finally able to get the tuner chassis out of the cabinet, and I looked over the wafer switch assembly and there was no burn spots on it anywhere it was practically spotless, except a little corrosion on the contacts which is to be expected on a unit like this of this vintage.

So I sprayed some contact cleaner on the switch and rotated it around several times and I hooked the unit up together on my bench and its still not working right it will only power on in FM Stereo and phono mode and that's it, AM and FM Mono mode won't work, and it does spark when rotating the knob but only when it hits the FM AFC (FM Stereo) mode, any other mode it won't spark, and I don't get any power from it.

Any ideas?