This classic Sennheiser MD421 Microphone came in DOA and deserved to live again. Some of these older mics have a bucking coil to reduce RF interference in series with the coil on the diaphragm – this one had an open circuit fault in the bucking coil and had to be unwound to the break and re-wound to complete the circuit. There are some very fiddly parts in the filter assembly in these mics so they are a very slow and steady type of repair job.
The old beast of a bass was not outputting signal from one pickup. In it’s old age corrosion had caused some intermittent connections through the switch and pots. The pickup circuit itself measured correctly so it was a fairly simple clean and re-solder connections throughout. All pots and the switch get a good spray with De-Oxit and it’s good to go. These Ricky’s are massive sounding basses and it’s a good feeling to help nurse these classics back to health.