A fairly simple trace of a lost audio channel in record mode. One channel was either intermittently or permanently not recording on one channel. Tracing the signal path with a 1KHz test signal applied to both inputs, revealed a break in the path, caused by either a recent repair mishandling or similar during manufacture. I suspect the former as the drive belts had been replaced sometime in the past two years, but NOT BY ME!! ;-) .
This fault proves that test equipment is essential. A test signal generator and some means to trace that signal. In this case a 1KHz audio test tone and an oscilloscope. Test generators are easily built and kits can be purchased on line, as can cheap oscilloscopes.
A simple repair to the broken circuit board was made, though a more elegant repair could have been carried out, simply reconnecting the component was sufficient. Once the fault was found, a full check and test was completed with no other faults discovered.
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