This grand old, 1960s MONO record player came in with the fault: "IT HUMS"

And no, the client didn't mean it had a bad odour, it was just making a very loud HUMMING noise. I recognised this as 50Hz Mains Frequency him coming through the amplifier, which meant either the input AC/DC conversion had failed or the output stage had.

Being easy to get into and glancing at the schematic, lead me to either the Bridge Rectifier Diodes or the Main Smoothing capacitor. The latter being the cause of the fault. Testing the capacitor on my normal DMM, lead to some erroneous readings, even when compared to a know good capacitor, so I tested it again using my component tester - built from a kit bought on e-bay.

That proved the capacitor had lost it's capacitance and required replacing. I had to fit a Radial type replacement as I didn't have an axial type of the correct value but it solved the problem. I then went on to clean the control pots and service the turntable mechanism, leading to a fully working record player. Hope you enjoyed the video.