My nightmare set: RCA 9T240

[Phil]

I've been working on a RCA 9T240 that has proven a real challenge. The set had been worked on previously by someone who made a mess of it. First of all the power supply was nothing like the schematic indicated. There were resistors that weren't supposed to be there and connections where none should exist. I started by putting the power supply back as it should be according to the schematic. I then made a list of every connection to the various power supply buses (two handwritten pages) and verified everything was connected as it should be. Of course, all paper capacitors and electrolytics were replaced and every resistor checked with any out of tolerance being replaced.

At this point I had a very out of focus picture which was way off the left side of the screen and terribly out of focus. HV was 6.5 KV. It seemed the flyback might be bad so I ring tested it with a Sencore VA62 and it tested bad. (see also my post in the test equipment section for more on this) I obtained a HVO-10 Merit universal flyback and in the process of installing it found that basically every connection to a terminal strip in the HV cage was wrong. I disconnected every wire from that terminal strip and reconnected it according to the schematic. After doing that I had a normal sweep and proper high voltage. The linearity was poor, but at least there was a picture. In the meantime I bought a HVO-3, which is a direct replacement for the original part. I installed it tonight and had an out of focus picture for about 15 seconds until it died. At that point I reinstalled the HVO-10 and now have a picture again.

Another issue I havent mentioned before is that the vertical osc. was way off frequency. There is supposed to be, according to both Sams and Riders, a 1.5M resistor from the moving contact on the vertical hold control to the rest of the circuit. It had a 4.7M when I started working on it. I had replaced it with a 1.5M. I have checked the circuit over and over and it all seems to be per the schematic. I replaced the 1.5M with a 3.9M and now the vertical with sync. This seems strange. Something must not be right. The vertical linearity is very poor as you can see in the attached image. Any ideas? It would seem the need to change that resistor would be a clue? Perhaps the vertical osc. transformer has problems?

Any thoughts would be appreciated.