[Joeztech]

This morning I took the chassis out of the cabinet again to look at the volume control and the distortion issue at high volume. I was distrustful of the audio coax that went to the high end of the volume control, so I changed it. It appears that short piece of coax has the shield grounded only at one end and is only a few inches long. I cleaned up some of the solder connections to the volume control. I had already cleaned the controls with Deoxit control cleaner. There is a tap on the volume element some amount above ground which goes to the tone control through a capacitor. I decided to look at the resistance measurements with my ohm meter to see what I could determine about the volume control as it is rotated. The strange thing is that with one end of the meter grounded to the chassis and the other connected to the center variable lug of the control the resistance goes to near ground when the shaft is rotated fully counter-clockwise and rises as it is advanced clockwise, then goes down for a space, then rises again to a very high value and then goes to close to ground again at maximum rotation. That is not  normal. The next step will be to disconnect leads and remove the control and open it up to see if there is some debris inside. One other thing I have seen with a few controls over the years is that some have a bit too much ability to rotate clockwise until the moving finger on the trace passes the end of the carbon trace enough to connect across the gap between the high end and the low end of the carbon trace. I hope that is not what is happening.

Since there is not a resistance path to ground through the tone control (or should not be according to the schematic) I do not see any apparent reason for the dip in the resistance to ground as the control is rotated clockwise. I will report on this later.

Joe