ARC Preamp going to full volume

Greetings Audiogoners. I'm having a serious problem with my Audio Research Preamp (Model LS15). I'm listening at low volume when all of a sudden the system goes to full output. At that point, before turning it down, the volume level as indicated by the LEDs shows a level consistent with the
lower output. I then turn the volume knob and the output instantly returns to the lower initial setting. The volume control is supposed to decrease volume in 1.5 db increments not jump like this. I wonder if the computer chip that manages the volume level is bad. I'm fortunate I didn't blow my speakers. Does anyone have any experience with this? Thank you for your insights.