Pam cooper, I’ve never worked on this exact device, but I have had other similar devices with pretty much the same problem.
Usually, what I have to do to fix it, is to replace some electrolytic capacitors on the board(s) inside. This is due to electrolytic capacitors being very susceptible to increased ESR (Equivalent Series Resistance). This can “destroy” (replacing the caps will un-destroy your device) your device. Getting an ESR meter off of Amazon and measuring each cap, then replacing those that are bad, is highly recommended (I’d probably replace all electrolytic capacitors). Audio- and visual circuits are very affected by bad ESR in caps!
Ceramic capacitors do not need replacing, unless physically broken, because they’re almost not affected by increase in ESR due to the way they’re made.
I’d start by opening up your device, and I’d take careful and good notes as well as good pictures of disassembling it. That way you have everything covered when it’s time for reassembly. Bonus: Create a [link|https://www.iFixit.com/Guide/new/|new Guide] so that others may benefit from you experiences ;) Next I’d go over all contacts and switches / pot meters with some form of electronic cleaner (preferably with deoxidising properties). Sometimes you’re lucky and all it needs is a good cleaning of the volume pots.