[jeyurkon]

I need some advice on dealing with a problem with the volume control on this set. It's a 1 meg composition pot tapped at 500K and 250K. It has a hollow shaft. The Photofact doesn't list any replacements other than Sylvania so it's pretty much going to be impossible to find.

The resistance from one end to the other is 1.2 Meg, which isn't so bad. The Symptom is that the volume jumps up to a loud leve when I start turning it up.

I've attached a scan of this section.

It seems that a spot was burned in the conductive film near the bottom of the pot. Possibly when paper cap C25 was leaky. As you go past this spot the resistance measured at the wiper jumps from 25 ohms to 250 ohms. If I measure the resistance to ground from the other taps they jump down to the correct value when the wiper is in the center of this spot. I imagine the conductive trace having a burned spot in the center of the trace, but good on both sides. I've attached a sketch of what I think it might look like.

I think the taps are there to keep the tone the same as the volume is changed. I could just short the 250K tap to ground. I'd lose a portion of the range. The tone might sound a little different. This would be the easiest solution.

I could try coating the spot with aquadag to cover the burned spot. If it's small enough, it might not be noticiable.

To get at it I have to remove the CRT, the front panel, and the plate that holds the pulley for the dial cord. I hope to avoid that.

Any other suggestions on how to attack this problem?

John