24  Mike’s Piece  Noisy Volume controls

Yet another domestic radio came for fixing the other day with the same old problem. The volume control was scratchy;  i.e. noisy when rotated. For those of you who are younger in the tooth,  I pass on to you the details of the operation I call doing a ‘volume-control-ectomy’.

But first you have to get the back off, which often easier said than done. Someone had to assemble the case so it should come apart again. In this case there were no screw-holes visible. Mmmm.
However, there were four small round impressions in the plastic back. Tapping a small screwdriver blade into these and turning them, revealed them to be a plugs bunging up holes and when removed, revealed the screw-heads. I was winning. But no, the back would not come off. Where else might a screw be hidden? Ah, remove the batteries. Is their a screw underneath? No! What then?

Ah, maybe the knobs all have to come off before anything will happen…………………………..no go. Look underneath and there’s some nice looking rubber feet screwed on.  Take them all out, just in case……….still no go. Pull up the carrying handle and lo and behold another plastic plug in a hole concealing yet another screw. Now the back is beginning to show signs of separating from the front. This maker was cunning. The back had been sprung into the front of the case as well, because when I squeezed the top and bottom of the back, it came off! Phew!

Oh dear, the tiny volume control is mounted directly on and under the board so it must come out. Find all the fixing screws first This board has little arrows marked on it to show you which ones to remove. Nice. Oh, the telescopic aerial is connected to the board with a soldered lead. Out with the iron and off it comes. Out comes the board and we can now get to the nub of the matter: fixing the pot. Switch cleaning fluid comes in pressurised cans, with a nice plastic nozzle, so you can get the contents to go where you want it. But no; can’t get in as the carbon resistance track and wiper arm are fully enclosed. This where the ‘ectomy’ comes in. Out with the hand drill with a tiny bit and carefully drill a small hole in the side of the case of the pot and then squirt away with a good dose, giving the spindle a turn or two to dislodge any loose, worn off, carbon particles. Put the batteries back and give it a whirl. Usually the scratchiness has gone and you can re-assemble the thing.

You did keep all the different screws in a suitable container didn’t you? An egg box is a good thing to have around in the shack for such occasions. You did make a note of the different lengths of some of the screws and where they went? A diagram helps here. You did remember to solder the aerial lead back on to the board in the proper place? Make a note on the diagram that you made. Good ideas.

But what if the treatment did no good and the pot is still scratchy? Can’t get a spare? If you are lucky there may be a tone control on the board as well. These hardly ever get used and so are in prime condition, so swap it for the volume control. Not the same value? Never mind, put a fixed resistance in the earthy end to make up the difference: no the volume won’t go right off, but so what. In one case I had, all I could do was to reverse the connections, so enabling me to use the less worn part at the other end of the track. So it worked back to front, who cares?       

   Vy 73 Mike G3JKX