BT/GPO 746 Dial Problem

[samaudio]

Hello folks,

I have a proplem with an old 746 phone. The dial was very sticky and slow on returning once dialed. I decided to unscrew the dial to se if there was anything obvious I could do. Unfortunately, once I had taken the clear plastic dial off, I unscrewed the 2 smaller screws underneath the dial and heard an ominous 'ping'.
Now the dial hardly works and has no tension.
Could anyone point me to a site that has information and diagrams for repairing this problem. Or does anyone have any other tips?
Many thanks,
Sam

[Nickthedentist]

Hi Sam and welcome!

The simplest solution would be to look for a new dial mechanism, especially as yours sounds like it was past its best anyway.

They often turn up on eBay for less than a fiver, and are frequently NOS or New Old Stock, i.e. are still in their unopened original GPO packing

Nick.

[AndiiT]

Hi,
You might find some information here http://www.britishtelephones.com/

Nicks suggestion of a replacement dial seems like a good one though, I too have never had much luck with slow/broken dials.

Andrew

[russell_w_b]

At the risk of inducing apoplexy in all the ex-GPO types here, I wish to add the following: not much use with a 746 dial admittedly, but I have had great success with the more substantial metal dial of the type 300 instrument.

These older dials can be stripped of their plastic parts and boiled in water for about 20 minutes to remove all grime and filth, then re-lubricated immediately with light clock oil - even WD40.

All I can suggest for the 746 type of dial is to apply judiciously some PTFE lubricant spray to the moving parts. Don't be tempted to clean it with 'Inhibisol' or 'Colclene' degreasers, unless you are sure that they are the sort of chemical that doesn't dissolve plastic.

Just thought I'd mention it...
--

Regds,

Russell W. B.

[Mike Phelan]

Hmmm - WD40 is not really a lubricant. Clock oil should be fine as it stays where it is. I did dismantle and lubricate a similar mechanism on my Avo CT160 valve tester.

Sam
Your "ping" was probably the spring that is pre-tensioned. Others will know more about this than I; someone will sort you out!

[russell_w_b]

When you took the plastic dial off, presumably you unscrewed the two small screws in the centre boss, either side of the dial mounting screw. As Mike points out, these screws retain the coiled-up tensioning spring (rather like a clock mainspring) held in the brass cup below the pulsing disc on the back. You could try:

• Removing the dial to expose the two nuts (on the same thread) that hold the pulsing disc in place on the brass spring-cup.
• Using a 7mm socket (pliers will chew it), wind the nuts and pulsing disc anti-clockwise. You should feel the tension increasing as you wind. Try not to let go, as the sudden release may take things beyond the point of repair!
• When you can wind no further, observe the two screw-holes on the front centre-boss, either side of the dial face mounting screw-hole. Release the socket slightly until the holes in the plate beneath align with the holes in the centre-boss. Remember that the spring is under tension. Don't let go too much!
• Insert the small screws you removed in the first place, locking the spring up.

To gain access to the governor and operating mechanism, all that is necessary is to remove the small spring-clip on the number disc behind the dial, which simply lifts off. Apply appropriate lubrication here. The governor should not normally need adjusting (I have found) and is held at one end in an adjustable brass cup, accessible behind the dial on the edge of the casing.

Don't release both nuts on the thread, as you'll lose the position of the pulsing disc in relation to the finger plate!

HTH

[Majicou]

Please please please never use WD40 to lubricate a dial. It will work for a short time but will collect dust and clog it up even worse than before. I can do dial repairs be they slipping cam types ( No10 ) or trigger types (No12 or 21 )

PM me if anyone requires help

Cheers

Andy