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OK, I think it's time for a recap on this thread.
I have replaced all the resistors and paper caps on the main PCB. The couplates were replaced with ones made by Bob. Under the chassis I replaced all the paper caps and most of the resistors, I left a few that tested good. K7 is original. The IF and tuner sections have not been touched. My 21EAP4 was/is weak, zapped it with the rejuvenator and it tests well into the green now and passes the life test easily.
Got the new modulator. I'm glad I had the test TV to get it set up correctly with, it took a few minutes to get the sound set right and so on. Hooked it up to the Predicta and I was getting a very unstable picture and no sound still. Since I'm more comfortable with audio, I started trouble shooting that and soon discovered that the 12CA5 looked ugly, I'm surprised I hadn't noticed that already. Checked voltages and the 140V supply was way low. Replaced tube and voltage came up but still no sound. Injecting an audio signal into the 12CA5 did produce a tone. Started working my way back and found a broken wire on the volume pot. Fixed that and still no sound. Disappointed, I was fiddling around with the fine tuning and what do you know, I got sound! The picture is a little unstable, but when it is locked in it is pretty good.
Remaining issues:
I have to tune for not quite the best picture to get sound. Best picture = no sound. The set tunes with the tuning control very close to one end. I see there is an adjustment pot next to the DIP switches on the modulator. Maybe tweak that to get the channel tuning centered? I found a manual for the modulator when at work and can't seem to find it now. I am feeding the signal to the set with coax and a balun, not transmitting and antenna.
When the picture has a lot of white, the sound gets way more buzz.
Horizontal control is unstable. It will lock for a while and then roll, sometimes re-locking, sometimes not. When rolling I get diagonal re-trace lines, sometimes across the entire screen, sometimes just in sections. It's easier to lock the picture when I have it tuned for best picture but then I get no sound.
12CA5 looks like it runs hot to me, it's lit up like a Christmas tree. And that is the socket that had to be replaced and the components around it look like they have been baked.
So many thanks for all of the help! Rio and I watched the set for about 3 hours last night and while the rolling was annoying it was still so much fun to watch. And when the picture is locked in it is more than acceptable. Once I get the dang thing to lock it needs some linearity adjustment, things are a little tall and skinny but not too bad. Really great to see this project start to come together!
Jonathan
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