Westinghouse vertical roll
 

Even after the recap and almost complete overhaul of the 17TV7C last summer the set began to progressively lose vertical hold control until it's at a point now where after about five minutes it doesn't matter where the knob is, it won't lock. All of the resistors between the vertical output tube were previously replaced by me. The vertical hold pot and a few original resistors remained as they were within tolerance. Tube also checked good last I plugged it in the Sencore. What baffled me more was I pulled the chassis out to poke around and change out another two resistors just in case and I couldn't get it to lose vertical like it normally it did. There was still a bit of touching the hold up but otherwise it remained rock solid for the eight or so hours I left it tuned into MeTV. Turned it on again last night to watch Murdoch Mysteries and nope, unwatchable after a few minutes. :sigh:

Hey Mips, I had a 17" Rogers set doing the same thing and it turned out to be one of those tubular ceramic capacitors. It was the one coupling the received vertical pulses coming into the vertical section. Changed it and rock solid, no more problems.

Gregb

It's a heat related issue - there's a component that gets warm and goes out of tolerance.

Get yourself a can of freeze spray. Or the 'canned air' at office stores. Turn it upside down.

You need chassis access here. Let the set run normally, until the problem appears. TURN THE SET OFF. The hit the suspect are with freeze spray. Try it again. If it's ok, let the problem re-appear. Repeat, but hit a smaller area (fewer components). Keep trying until you narrow it down to one component. Replace that one.

I had this with my Bendix a few months ago. It takes a bit of time, but once you find the bad part, you'll know it - because hitting it with spray ALWAYS fixes the problem for a while.

There's no need to turn the set off. Just watch the screen (using a mirror if necessary) while hitting each part individually with the spray.
We used to use a movers quilt over the set to get it warmed up good, before going in with the Freez Spray. A hair dryer would probably work as well for a jiffy warm up.
Is 'canned air' actually cold enuff to work? We didn't have that back in the day.

I actually considered thermal issues as well but never considered the hot air gun trick. I could give that a try and see what happens.

I agree that its the input coupling cap from the sync separator. As caps get old they no longer pass low frequencies (30 Hz.) but they do continue to pass high frequencies.
Does that set have a vertical integrator network? Thats a three legged ceramic network. They go bad too but can easily be duplicated by discrete components.

Be Careful some "canned air" is highly flammable !

Have a nice day !

rrrhre2s

look into micas if there are any in the verticle section, they do go bad, rare but they do.

We do have a hybrid circuit, yes. Connects from pin 6 on a 6U8 (Sync Nosie Sep. Lim.), through itself, a 22K resistor, .01 cap I replaced and to pin 1 on the 12BH7. Seems to consist of three resistors (22k, 8.2k and 8.2K) and three capacitors (.002, .005 and .005) While I was trying to figure out my width control problems I was testing it on the bench to see if it least ohmed out right and that seemed correct but never tested it any further.
I know someone here has a copy of the schematics. My digital copy is currently on a server which is a little...sick.