PG505/Repairs
Power supply
A PG505 that was described by a seller as "no variable frequency" showed an erratic output signal that partly responded to output voltage and rise/fall time controls, but was essentially at mains frequency.
The source of the problem was a dry electrolytic (C555) in the floating power supply. Because the floating output stage is transformer-coupled, the output pulse was effectively triggered by the pulsed supply.
The electrolytics are physically large and soldered on four voluminous pins, therefore removal is not easy. Modern replacement caps fit on the solder side of the board in parallel, however, with Kapton tape for extra isolation.
With the usual cleaning of switch contacts and pot wipers, full function was restored.