> The comp. out of my 3rd envelope is failing to trigger the 4th
> envelope. Is this a common problem Would it be a jack problem
>
> I would welcome any advice.

Connect CP3 out of unit #3 via an external patch cable to the trigger input
of unit #4. If then unit #4 triggers again probably the switching contact of
the trigger in socket of unit #4 is worn out or broken and the socket has to
be replaced. Otherwise something elso is wrong.

Best wishes
Dieter Doepfer