191/Repairs

R58, the variable amplitude potentiometer is prone to failure and is usually the reason for symptoms such as scratchy amplitude modulations, incorrect amplitude output, or instrument unresponsive to calibrated amplitude controls. Sourcing an exact fitting replacement for R58 is difficult and it is recommended to try and salvage the faulty potentiometer.

R122 is a potentiometer responsible for regulating the -11 V supply rail. Over time the lubricating grease inside the potentiometer tends to harden or become very viscous to the point where it becomes very difficult to make any kind of adjustments without damaging the shaft.