COld Solder/Short

Before taking anything apart, if the TV is on legs, try propping it up in the normal position so the legs are just off the floor. If this does nothing it will show it is not pressure distorting the cabinet.
If it does the movement of the cabinet must be shifting something on a PCB, such as a dry joint or a plug/socket.
In modern sets there is no chassis; the Printed Circuit Boards are usually clipped and screwed directly onto projections inside the cabinet.
The dangerous high voltages are usually well insulated and confined to one PCB.
A PCB for control is usually in the bottom of the cabinet, and this is the one you should look at. It only has low safe voltage on it.
The mains lead goes to the PCB which also has high voltages for the power supply; if this is in the bottom of the cabinet also then suspect a fault on it, but beware you really need an expert.

The silver box where the cable plugs into is the TUNER,there are no fuses in there and the problem is not likely to be there,the loose conection could be anywhere but you have a few places to check,with the tv unplug from the wall you can safely check for loose conections in the power supply area and around the output transistor including the areas of the horizontal drive circuit and output transformer,those are the areas most likely to the symptoms you have but you can also check the edges of the chassis for a broken or crack board.Let Us know if you need more help.Be careful when you are checking for conections.

Ok, so it's the tuner. That makes perfect sense. With the back off, nothing seems loose. The PCB is basically to the right, under and behind the CRT. I had it working for about two hours, then it pulled it's old tricks. Should I pull the PCB, or do you think tapping with an insulated screwdriver on various components would do the trick? I'll be careful not to short a connection. I don't really like poking around in an unfamiliar region, but I can R & R any component, no matter how small the solder. I've fixed power supplies for my studio, and I've done audio gear. It's the high voltage that worries me. I don't want to smoke a component. Supporting it other than on it's base is a good idea. I'll suspend it from it's sides and see if "chassis" flex is what causes it, or if it's directly related to a component moving when it's level, and back again when it's leaned forward. You are correct that the PCB is mounted directly to the base.Thanks for the really good info.I appreciate the help.