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Remove the back cover and locate the tuner. That's the metal can with a cable going to the coax (antenna) input jack. Near the tuner, there should be a smaller metal can. This is the IF assembly. Unsolder this assembly from the chassis. You'll have to unsolder the pins as well as the four metal tabs from the main PC board. Now, unsolder the shield from the IF assembly PC board. Once the PC board is exposed, you'll see several variable inductors in small metal cans. These are prone to have loose connections where they solder to the IF assembly PC board. Resolder all of the coils to the PC board, making sure that you don't solder any two terminals together. This board is sort of compact. Also, resolder the terminals on the IF assembly. Re-assemble everything and it will probably work fine. This was a common problem on Sony's from the '80's and early '90's.
Not related to your problem; but, resolder the degaussing thermistor while you're in there. Those were bad about getting hot and breaking away from the PC board.
Those KV1972R's are good sets. I've got one that was given to me by a TV shop. All it needed was a new bridge rectifier and a resistor and I've been watching it for around 6 years.
Just remember to unplug your set while working on it and use caution when powering it up with the back off. There are high voltages inside and the chassis of that TV is "hot".
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