Failure of Jeff Rowland Model One

My Jeff Rowland Model One is stuck in stand-by mode. Pushing the front button nothing happens (*).
Any suggestions to fix this issue?
I would also appreciate any suggestions for disassembling the unit, as this does not seems so easy.
Thank you very much.

(*) In a working unit, pushing the front button causes the passage to operating mode, and you can hear the click of a relay and see the indicator bulb increase in brightness