Hello all! I have yet another perplexing problem with my 1972 color Zenith with the 25CC50 hybrid chassis. The problem is, well SNOW, in every condition of operation. Even with a DVD player hooked up directly to the TV, I just can't get a clear picture, there is still snow. I have done all of the prelimaries, I changed both of the tuner tubes, and the 3rd video IF amplifier tube, the rest is transistors (havent messed with those). I tried fiddling with the AGC, this had no effect. I even cleaned the tuner contacts, nothing. I am actually a bit lost right now. Anybody have any experience with this problem on this chassis?

I would try and run the output of another known good set's tuner into the IF input of the Zenith (make sure neither one is a hot chassis set) This will tell you if it's a tuner or IF related problem.
Did the set ever have proper operation since you got it or did the problem suddenly occur?
If you have a decent strength UHF station available, does it come through OK or is it snowy too...this test will help rule out problems in the VHF antenna input circuit.

Haven't personally seen this problem in Zeniths but have seen it in RCA's which use a transistorized IF stage and the rest is tubes... the problem turned out that there was a power supply problem leading to abnormally low voltage supply to the transistor stages.

Actaully, I did forget to mention that the UHF comes in great, no snow there. I have had this problem ever since I had the set. If it is a voltage prblem will simple meter readings isolate it?

Is the tuner a tube type version? The 6HA5 is ALWAYS weak in those sets. Also, does the 25CC50 have an RF DELAY pot (aka AGC delay)? If the tuner is solid state, I bet I have one. I have several spares for my 25DC56 & 25EC58 sets, which had the same tuner mounting as yours (if it's the one I saw at your Dad's place in a back room)

Charles

PS: I need to get this CTC-12 cover plate, and your Mustang book to you!