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"
Problem solved
The wire in the loom between the resistor and bank outlet 19 was dis!
Possible reason
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
S&T
Sort of followed your blog as a friend was a PO engineer many years ago and I recognised the terms used. Thanks for the update.
ReplyDeleteRegards, Paul.
However I did not follow all abbreviations.
ReplyDeleteWhats dis, HR ?
Dis = disconnected. HR = high resistance (typically occurs when connections get oxidised or corroded)
DeleteSo know you know, keep up plse!.
DeleteAlso FNF, and RWT was useful as clears on Special Faults.
M
Thankyou Mike for the update, still don't know how these really work so thank goodness you understand how it does!
ReplyDeleteRegards
Paul & Marion
This PAX (PBX?) talk takes me back many year. I joined the GPO 52 years ago and spent the next 18 years working on Strowger - RND, UAX 7, UAX 12, UAX 13 and UAX 14 - before winning a management role where i spent 34 years until finally retiring end of June this year. I left my old tool box behind still with uni brushes, detent pins and adjusters of all sorts. Happy days indeed, out in a 'shed' alone or with one other engineer.
ReplyDeleteOh Crikey could have made use of some of those tools!. Uni Brushes and Bank Tape are in very short supply especially the yellow tape.
DeleteAmazing how it does come back yto you, I find that first thing in the morning is best- its over 50 years since I started an a Y3YC in Shaftesbury Avenue.
Helpful field guy retrieved my toolbox and delivered it to me - mysteriously minus uni brushes - if you still want some tools.
DeleteI find it interesting that you use yellow tape to bank clean - during the twilight years of the exchange where I was a TO ( Leamington Spa ) we only used yellow on the most tarnished/burnt banks, plain cleaning heads being the order of the day as the yellow cleaning compound created noise issues only cleared by doing the banks again with plain tape heads ( what a pain that was). There was an experiment done oiling the banks with contact cleaner/lubricant from RS - what a disaster! arcing all over the banks caused by the dust sticking to the oil! the noise on calls was epic! - keep up the good work! I'll ask around my ex-colleagues if they have any strowger spares in their garages!!
ReplyDeleteThanks, that would be very helpful.
ReplyDeleteWas it Mark Twain who said " By old stuff, they ain't making any more of it?"
Well almost that!
Thanks again
WE have a box of a much later type of cleaning head, sort of stacked white horseshoes, but we don't have the tool to drive it. We just use the original sickle type, one level at a time
ReplyDeleteM
Just wondering if these telephone exchanges are the ones that my father obtained for the railway in the early 1980s when he worked for Plessey's
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ReplyDelete