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Here's my 2 cents worth.
On the CTC177, I think they're pretty good sets, except for one major thing, and that's the "tuner-on-board". You've probably noticed that the tuner can't be removed, because it is part of the main PC board. They had zillions of those sets fail because the ground connections to the shield around that tuner would pull apart. It was a thermal thing. The board would expand at a different rate than the metal, causing the solder to crack. When the connections to the shield cracked, various parts of the tuner that needed to be grounded weren't any more. The shield was the only ground connection to some of these areas. They tried a bunch of stuff to fix the problem-different alloys for the shield was a big one. Some of them were made of copper, and you needed a blowtorch to get them hot enough to resolder the shield to the board. I don't see the coppper too often, but I hate it when I do. They also added some additional traces/jumpers to tie ground points together. That helped some. There was a special solder kit that they told us to use to resolder the shield to the board, and it was supposed to be flexible enough to move without cracking as the set warmed up. It came with a tube of flux, and it was messy to use, and seemed to eat up soldering iron tips. But it worked. There were also 6 jumpers to be installed in the tuner, so if the shield came loose again, the wires would keep these critical areas grounded. Another fun aspect of this problem was that if the customer continued to use the set after these connections failed, in addition to tuner type problems, it could kill the memory for the micro, and you could have all sorts of funny stuff happen, from scrambled displays, to a dead set.
Back in '94, when they told us about the design at a training session, a couple other guys and I approached the Field Engineer and expressed concern about how the was grounding was done on these sets. He insisted that all the problems were worked out in advance. I always thought he was concerned too, because his answer sounded like a corporate script.
I guess I shouldn't complain about them though. I made a ton of money fixing them. Still see one every month or so, for the tuner problem. If yours is OK, it was probably serviced sometime in the past. Some stores started sending all of them in for service as "store stock-defective" because so many had failed soon after being sold, and the returns were killing the stores profit.
As for the power supply, I didn't see an unusual number of failures on these sets. Early sets did have a couple minor bugs I know about, but they changed the part numbers and I dont see those problems anymore.
The Zenith
Always makes me nervous to go out on a call on those, because after the power supply fix, you fire it up and the CRT looks awful. Zenith CRTs have made me nervous for a long time.
The power supply probably failed because a little 100uf/25v cap changed value to somewhere around .000000000001 pf, with a lot of ESR. Then the IC goes poof, along with couple other things.
The GC648S
Chassis is CTC92
My advice for a set today?
Hit the thrift stores and find a 1979 RCA or Zenith. If they ever break, you fix them. If a new set fails, it is likely to be dumpster chow. If you did want a modern CRT set, Sony and Toshiba are pretty good, but I don't think they will last as long as the old sets do.
I could keep spewing for hours, but I've already spent way more than 2 cents worth, and the kids yelling for pancakes, so its time to take off the TV guy hat and put on the daddy hat. Hope this info is of value to you
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