We had come to the conclusion that the problems were not necessarily obvious from the diagram so we had to think outside of the sheet of paper.
Bank cleaning was well overdue and we wondered what effect sticky banks would have on the release process- was this allowing something to go out of sequence?, not a situation that I have ever met before.
So off we set with a manual bank cleaner and yellow tape, doing three banks for now just as a trial. +
Also, whilst the selectors were jacked out it was a chance to look at lubrication particularly around the shaft area. I have long believed that with older kit its best not to fiddle with it any more than you have to- indeed AT&E later discontinued all routines as they found they introduced more faults than they cleared. I understand that the GPO also took the same view in later years (1970's).We then busied the selectors that we hadn't serviced and low and behold the fuse blowing ceased as did other odd symptoms.
The problem then settled down to permanent engaged on the first tie line. AT&E called it the D wire (aka PO P wire) to test for line engaged or free. We should therefore have tested a 150ohm battery condition on Tie line 1 but we didn't. We did on Tie 2 but not Tie 1
All the time we kept going back time and again to the same question " what had changed since shutdown"
The wire in the loom between the resistor and bank outlet 19 was dis!
Perhaps the current surge which was causing the fuse to blow finally burnt an air gap in a crack in loom?? and standing for three months allowed it time to oxidise and go HR?
Who knows, but we left it all working once again.
Next Visit: Bank Cleaning and lube check
Mike Stephenson and Paul Dinucci