The Denon UD M30 is a rightly popular mini system which delivers excellent sound from a unit the size of a shoe box.
Mine was purchased as a replacement for a very nice Marantz separates system which would not fit in our newly decorated lounge. The bijou Denon gave the Marantz a run for it’s money, much to my surprise. Unfortunately it recently developed a problem with the volume control.
The problem manifests itself when you turn the knob and the volume suddenly shoots up to a deafening level. This is a common problem on old Denons. I have discovered that it is caused by the lubricating grease on the volume control getting into the wrong place and confusing the digital controller electronics, which actually controls the volume.
Here you can see the volume control taken apart. The three brass contacts press against the metal disc. As you turn the control the contacts are connected to each other in sequence. it is this sequence of on-off actions which the controller interprets as the knob turning.
In this picture you can clearly see that the contacts and the disc have a liberal coating of grease. This shouldn’t be here. The grease actually conducts electricity well enough to cause all sorts of problems. The grease was originally installed on the control shaft and provided that pleasant resistance to movement which made for an “expensive” feel to the control. Over time the grease found it’s way into the main body of the switch.
To fix the problem you need to remove all traces of this grease from the contacts and wheel. I took the whole thing apart and cleared grease from the entire switch mechanism. This meant that the control no longer has that expensive feel, but it does work properly.
As always with such things the fix is fairly easy, but gaining access is a bitch. This is not quite a “first reduce your appliance to it’s constituent atoms” situation, but it’s not straightforward. The front cover needs to come off and the PCB housing the controls needs to come out.
i’ll finish with some high resolution photographs so you can see how it goes together.