[Premium-Rx] Help with a WJ-8711A

[William Watson]

My trusty WJ-8711A has developed a problem.  The AM bandwidth selector is locked on 6000 and no longer lets me adjust it over the BW range.  Was working fine and after I opened up the front panel to apply cleaner to SPEAKER control it stopped working. Speaker control works fine now, but the BW is broken, as stated.
Any suggestions re trouble shooting this problem?
Joe WatsonW5WBR