have you tried cleaning the controls? some directions are posted at the top of this forum.
Talked to a Pionner repair person here in Portland who knows this problem. The unit I have, the volume control turns in both directions un like some models. After answering the question about the control itself he said that the Portentionometer ( sorry about the soelling) needs to be replaced. He has the parts in stock.
I have not tried to clean the volume control itself could not find the procedure and do not want to do something wrong. It seams if it was a dirtty volume switch the the switch would be noisy when turnned. In my case I do believe it is the volume control part it self. I guess it would be the part the volume knob is pushed into.
Thats it for now