First of all, sorry for the long post!
This might be something that could be easily searched, but I really don't know where to start. I bought a cabinet style TV last year with the intentions of only using the hardware to install a new flat screen. However, I tested it out and found that the TV had a great picture already! Unfortunately, the vertical hold will not stay correctly adjusted. If you try and adjust it over a period varying from about 10 minutes to an hour or two the vertical hold will fall out of adjustment. I have a basic familiarization of electronics, I repair electric motors for a living, but Im a rookie when it comes to TV repair! Im at work right now, but plan to post pics tonight so everyone will know which TV I have. I believe it was made around 75, there was a sticker someone ripped off that covered up the Motorola address on the rear, I've heard that was done around the time Motorola sold off their Quasar line of TV's

I recommend getting the Sam's PhotoFact folder for that set before tinkering with it. The Sam's should contain the schematic, photos of the inner workings to aid in locating specific parts, and instructions for preforming certain adjustments that may or may not need to be done.

That said if you have an oscilloscope at your disposal I'd start (once I laid hands on the Sam's) by using it to check the waveforms coming off the synch separator, and certain points in the vertical stage. I'd watch the scope as the vertical lock varies to see what is changing during warmup and start checking parts around the point where the waveform varies with warmup.

If you can get it to always synch up, and only have to readjust the hold once or twice during warmup to keep it in synch then it maybe easier to live with it until it gets worse, but it sounds worse than that so repair may be necessary.

What are you using as a signal source? VCRs tend to have funky synch that does not always agree with older TVs so if you are using a VCR as a signal source I recommend trying a DVD player, older video game console, cable, satellite, or a DTV converter box to see if it still acts up with a signal source that has better synch.

Older Motorola era Quasars are nicely made sets.

I wish you luck in fixing it.

A can of freez spray ('circuit cooler') with a fine straw applicator will often quickly identify the heat-sensitive component(s). Radio Shack sells it last i heard.

Not bad for an $8 TV.

Electronic M, Ive tried my DVD player and my DTV box, the TV acts the same with both. I saw here, http://www.videokarma.org/showthread.php?t=246445&highlight=quasar that you can pull the chassis out from the front. Is that possible on my TV too?

Hmm, I just quickly answered my last question! http://www.youtube.com/watch?v=4DZjvWy9ZfA

Nice find-you did good! I'd suspect a capacitor or maybe resistor which is changing value as it warms up, as old coot said. Pinpoint where the vertical circuit is, then spray the individual parts and see what the picture does. If you can make it change with a burst of cold, change that part and see if that clears it up. It usually takes 5 seconds or so for the cold to sink in after you spray.

Holey Cow!

That is the same model and cabinet style set I had as a kid.
Some of my first memories of watching TV as an infant back in the 90's were on one of those. Seeing as there are at least two of those left around it gives me hope of finding one for my collection someday.

That looks like the set I had in '98-'99. One of the heaviest consoles I ever moved. Up 15 feet of stairs. Mine was made in late '75 and had a brass emblem from some furniture manufacturer (in Penna.?) nailed to the back of the cabinet.

I'll try the freeze spray. What do I need to find the Sam's photofact? I can't seem to find anything on the back like a model #. Tonight I'll pull the TV away from the wall and use a flashlight and see if I have any luck. You're right, it's a heavy set! If it ever goes completely out I guess I'll have to gut it out in my living room! I spent years looking for the perfect TV to go into my 70's living room! It matched the Magnavox stereo cabinet that I already had quite well!

See if you can find a number starting with TS-. Might be stamped on the chassis somewhere. We might still be able to narrow it down without that information, but that would make it easier. Several of us on here could provide you with a copy of the Sams, I've probably got a spare myself.

You can also use computer keyboard cleaner "air" cans turned upside down as a freeze spray.