First thoughts were that it was a power supply problem, but everything looked fine when the oscilloscope is connected. The buzzing was the same no matter what the volume control was set to, which led me to investigate the audio power output stage; in that area there are two transistor bias circuits that could have caused the problem, and it was a matter of elimination to find the faulty one.
A new 150uF capacitor is fitted and all is working again. Or so I thought…
The radio worked fine, but when switched to ‘turntable’ (or in this case “G” for Gramophone!) we find the record is struggling to turn at the right speed, also the speed selector doesn’t work properly. A few drops of oil on the selector shaft and a clean of the idler wheel brought this all back to life.
In total the new component was 29p, I had to buy the circuit diagrams, and there was about 2 hours work so £25 charged in total