746 dial sticking and question about adding buttons

[BGmidsUK]

Hi, just a couple of quick questions about my 746.

The dial is sticking in about 3 places throughout its travel when you operate it, as if there is some obstruction in the gears, this only happens when I rotate it the first time and it always returns smoothly - no problem dialling out - and subsequent rotations seem smooth enough. This lasts until the next time the phone is used so I wondered what could be causing it and whether it will be fairly easy to remedy - as I've never taken a dial to bits I don't want to dive straight in without asking first and possibly end up with a "sprong" and parts flying in all directions!

The other question relates to adding a twin switch so that the bell and microphone can be muted - has anyone done this and is it simply a case of using a latching SPST for each, one to cut the bell supply and one to short the microphone, as I would assume? Or are there any other modifications needed such as a dummy load for the microphone? If I can't find a twin button I'll just go for the privacy option.

Sorry to sound daft but I'd rather not involve a call-out from Virgin


BTW call quality is lovely on this phone, far better than those DECT things


Brian

[Geologytom]

I'm not the most technical person here, but I noted your first issue, and having fixed a similar sounding one yesterday, I thought I would share...

One of my 746's kept sticking because it turned out the dial was fouling on the decorative plastic ring, because the metal band holding the dial to the chassis inside the phone was not tightened up enough, meaning the dial was not central to the hole in the casing. As you have new casing (the purple!) it could be possible that things have been all played with and not quite lined up. Try releasing the case, does it intermittently stop then?

If it is within the dial itself it sounds worrying, could be a number of things...try reading this amazingly detailed page at Bob Freshwater's telephone site.

http://www.britishtelephones.com/dial1.htm

The other question all I can offer to is that I have a number of handsets of various ages with push to make simple switches that mute the receiver very simply by cutting the connection in the handset, if that helps?

[twocvbloke]

In my thread on my 746 I bought today, I just found that the dial gearing was bone dry and needed a few crops of oil, that freed it up and is now spinning as fast as the dial in my linesman phone...

Surprisingly it's not that difficult to work on, I was expecting it to be difficult, but it's only a few screws (leave the contacts in place though, that was fiddly to refit!!!), on my phone it was the gear connecting the hub to the governor, and the the tip of the governor that needed the oil, they don't really need to be removed, but give the gear a little time to let the oil soak in...

[BGmidsUK]

Thanks, I took the dial off and put some lubricant on the gears and it does seem smoother but I'll try it again in the morning to see if the sticking is back. It takes roughly 1 second to dial zero, it always returns smoothly once the dial is released.

There is no evidence of muck or any wear/damage to the gears that I can see.


Brian

[Darren-UK]

Note there should be some slack between all meshing parts of the governor drivetrain, including at the worm. If this is all set correctly, oil shouldn't be necessary. Also, make sure the governor doesn't have too much axial play and that the cup is securely fixed.

Beneath the governor wheel and out of sight when the wheel is in situ is a clutch. When dialling, this clutch disengages the governor drive and then engages whilst the dial is returning. If the clutch is gummed-up, that can cause the symptom you describe. I had the same problem once on an older Type 12 dial; some IPA followed by a spot of light oil whilst turning the pinion by hand cured the problem.

On the matter of muting, providing you're remaining with the telephone you can cheat and mute it by simply moving the dial a few degrees and holding it there until you want to unmute again.

[BGmidsUK]

Hi, thanks - I took the dial apart today as it still got "caught" about ⅔ of the way round the dial on its first rotation. There is no significant contamination on the clutch (which I gave a slight dose of lubricant, as I had with the other gears, to save wear) and as before, subsequent rotation met no tangible resistance. It all looks in good order. I wonder if it's actually the spring catching on the metalwork behind the dial, I've given that a bit of grease as well. I'll see what happens tomorrow when it's been left idle for a bit.

Good tip re. muting, though I'll need to experiment with this to make sure the caller/callee really can't hear the rude things I'm saying when I've got their video or computer in front of me


Brian

[AndiiT]

Originally Posted by BGmidsUK

....The other question relates to adding a twin switch so that the bell and microphone can be muted - has anyone done this and is it simply a case of using a latching SPST for each, one to cut the bell supply and one to short the microphone, as I would assume? Or are there any other modifications needed such as a dummy load for the microphone? If I can't find a twin button I'll just go for the privacy option.
Brian

Hi,
you won't require a dummy load for the transmitter, just arrange a switch to short out T3 and T10 in the telephone instrument. For bell cut - off fit a single pole switch in place of strap T17 - T18.
If you aren't too bothered about drilling holes in the case you could fit the switches either above or below the dial, on the left and right hand areas, on the sloping part of the case, there should be enough clearance underneath the case but it would be best to check first, suitable switches would be ones such as these available from Maplins

If you wished to go a bit more advanced you could also/alternatively fit a "Hold" facility by wiring a switch, in series with resistor of 150 to 470 Ohms across T8 and T18, if you did fit a hold facility it might be best to use a double pole switch and use the extra pole to operate some kind of indicator lamp as a "call held" reminder.
Additionally if the telephone has extra terminals T19A and T19B these would be a better alternative to T18 as using one of these terminals would prevent the line being accidentally held when the phone was on hook.

Regards
Andrew

[BGmidsUK]

Thanks for the info Andrew, this is very helpful. I wouldn't want to drill the casing as a non-standard switch would look out of place, what I would like to do if I can get hold of one is to fit a (preferably latching) button where the blanking plate is. I've had a look around and can find single buttons but haven't seen anywhere selling the actual switches yet.

If anyone has a photo of a switch mechanism fitted it will be great, I haven't actually seen any pictures of 746s with twin buttons fitted though!


Looks like I'll live with the slight sticking on the dial for now as it doesn't appear to be getting any worse, less so if anything, and only affects the first clockwise rotation. I'll tackle it if needed. I think it's nothing more than the spring sticking a bit to be honest.


Brian

[Dave Moll]

The switch mechanisms do turn up on eBay from time to time.

[AndiiT]

Hi,
I don't have any of the split buttons, but might be able to sort out a latching switch (Bell on/off, but I suppose you could use it to mute the transmitter instead depending on how you wired it) and button/spring/plunger assembly for the cost of postage for you.
Some details about fitting these are around halfway done the page at this link

An alternative would be to try and obtain the casing for a 740 type telephone, which has positions for four switches; The 746 can take a maximum of four switches and plungers between the switch hooks.

Originally Posted by BGmidsUK

.If anyone has a photo of a switch mechanism fitted it will be great.

I'll see if I can post some pictures of a 700 type phone with switches fitted for you later.

Originally Posted by BGmidsUK

I haven't actually seen any pictures of 746s with twin buttons fitted though!
Brian

Take a look at http://telephonesuk.co.uk/images/lar..._2_buttons.jpg

Regards
Andrew

[AndiiT]

Hi,
As promised pictures of switches mounted in a 746, these are from the phone with a latching switch assembly the non - latching ones are in the following post.

Regards
Andrew

[AndiiT]

and the non - latching ones with twin buttons

Andrew

[BGmidsUK]

Many thanks for the pictures, I've sent you a PM re the switch parts.


Brian