You can try to clean and lube the original trimmers (worked for me).
If that isn't your solution, try to find a pair of Bourns 3252-W-1-204 (avoid the 3252X with the SIDE adjustment). They are vertical adjustment, 25-turn trimpots, 3/4 watt dissipation with 200K resistance. That should work fine since they are installed with the wiper common to an end (rheostat-mode) and will easily adjust down to the 150K range of the original. They are much larger than the standard 0.100" spacing trimmers at ½" square with larger, longer leads more suitable for 1970s style discrete component boards. Your adjustments will be a lot finer, and tend to stay put because of the worm drive mechanism. The ½" long leads should permit reforming to reach the through-holes of the board at the original trimmer spacing.
You can find them at DigiKey, Mouser, Allied, Newark, etcetera for about $12 apiece. Your local shop may also have something close.
If that isn't your solution, try to find a pair of Bourns 3252-W-1-204 (avoid the 3252X with the SIDE adjustment). They are vertical adjustment, 25-turn trimpots, 3/4 watt dissipation with 200K resistance. That should work fine since they are installed with the wiper common to an end (rheostat-mode) and will easily adjust down to the 150K range of the original. They are much larger than the standard 0.100" spacing trimmers at ½" square with larger, longer leads more suitable for 1970s style discrete component boards. Your adjustments will be a lot finer, and tend to stay put because of the worm drive mechanism. The ½" long leads should permit reforming to reach the through-holes of the board at the original trimmer spacing.
You can find them at DigiKey, Mouser, Allied, Newark, etcetera for about $12 apiece. Your local shop may also have something close.
