[HAM] No vibrato - T-412

[David Damroze]

  Model T-412 : I here a change in tone when I flip the vibrato 
switches, but, no vibrato.
   I did search the archives but didn't find much on this issue.
   Any simple fixes,or, is it likely to be somewhere in all them there 
silicon thingies ?
I want to get it sellable and use the money on the M-100 :-)

  David D.