1972 Zenith color TV is back to life!

[drh4683]

Here's the '72 zenith. Its up and going again as of this evening. The new 6JG5 tube came in the mail today.
I replaced the 2.2K resistor in the cathode of the 3.58 osc. and the 68 ohm resistors in the chroma module which went up in smoke. Most likely due to the shorted out 6GJ5. After powering the set up, everthing was fine but no HV of any kind. The B+K analyst was used to clear the sweep transformer, which was all fine. This lead to troubleshooting at the horizontal output and back. There is supposed to be -58 volts at the grid (pin 5) of the 6LB6, which was actually running at +150 volts!!! Flipped the set over and first thing was to check the plate voltage at the 6U10 horizontal oscillator tube. The voltage was non existant. B+ was at the other side of the 39K 1watt carbon resistor in the plate circuit. That resistor was wide open killing the plate voltage. It looked perfect though. Put in the new 39K and everything was back to normal. The belfuse connection was a bit intermittent though at the cathode of the 6LB6. Simply bent the prongs out on the socket and all was well. I had to pull the tuner out to clean it, and also had to detach it from the mounting bracket in which to put the sheild back on. This is where the original owner screwd up. There were two left over screws sitting inside the cabinet, which were intended to hold the tuner bracket to the CRT bezel up at the top. They can easily be loosened and then the tuner lifted and pulled out. Speaking of the tuner, I had to take a picture of that disturbing tag I saw. Made in HONG KONG!! The zenith super gold video gaurd turret tuner made in Hong Kong, say it isn't so! Zenith was ahead of its time in more ways than one. They were one of the pioneers in oursourcing US jobs, which is one of the things I'm not proud about with my favorite electronics manufacturer. If I'm not mistaken, the very LAST all USA made parts in a Zenith TV would be 1967. 1968 models started to use the portugese made deflection yokes. As the years went on, you see more and more foreign parts inside the Zenith TV's. Lots of capacitors from japan, yoke from portugal, parts from hong kong like the delay line, tuners. I wonder what the zenith employees thought about that back then. The concept of outsourcing was relatively new then. I don't know when I first started to see Hong Kong made turret tuners though, this must be one of the first. My '70 models have USA made turret tuners. However, UHF tuners I've seen made in Tawain since the '68-'69 models. They were obviously made in a Zenith plant though, the quality is still there, just like the Taiwan made B+W sets from the early 70's.

Anyway, now that its fixed, its a typical zenith performing TV. Perfect picture. Just need to touch up the convergence and pincushion phase. All voltages test within spec at the oscillator and output tubes. This TV is getting its last gasp of true NTSC TV!

Pics are of the 25CC50 chassis, which I think is a pretty neat chassis. This one has 12 chassis tubes, 10 plug in transistors and one IC. I like these hybrid sets with the single duramodule. This chassis is very similar to the 1970 12A12C52 which is my favorite TV chassis. '72 is the last year for this style of chassis.