I found this small, yet very important detail on a DB-37 connector attached to the back of a Nautel V-1 transmitter:
The black wire is the ground wire and the orange wire is the remote RF off command. A closer view:
The transmitter had been shutting down unexpectedly since it was installed. When these shutdowns occurred, there was no overload, no fault, no power interruption or other indication of a problem. When the RF on command was issued, the transmitter would turn back on and run with normal readings until it shut down again. It was a bit of a mystery; the transmitter was removed from its mountain top home and hauled back to the shop to be repaired. It was connected to all sorts of test equipment and studied intently for many days. Still, the problem could not be replicated in the shop.
Then the transmitter was hauled back to its mountain top transmitter site and re-installed. It ran well for about a month and then started going off again. This time somebody looked at the event log and noticed that a “Remote RF off command” was being issued at the same time the transmitter would shut down. Ahhh, the missing bit of critical data. That prompted me to take apart the DB-37 connector used for the remote control interface. The problem was obvious as soon as I removed the hood.
Sometimes the most valuable piece of test gear is the venerable Mk I, Mod 0, EYEBALL.
I unsoldered the ground lead and put some heat shrink over the connection to the DB-37. Hopefully, that will take care of it.