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Old 29th Oct 2009, 12:36 pm   #1
retrotelecom
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Default Another 700 series question (TMA 7214)

I have a what appears to be a 706 with bell on/off switch, but it is actually stamped on underside as TMA 7214. So far I've failed to get it going. Has anyone heard of this telephone - I have looked high and low for ref to it/wiring diags with no luck at all.
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Old 29th Oct 2009, 1:11 pm   #2
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Default Re: Another 700 series question

TMA means it was manufactured for the GPO by the Telephone Manufacturing Co. at their Airdrie factory. This company eventually became part of Pye. TMA was one of a number of codes allocated to TMC by the GPO.

I don't know of a cct for this instrument but it's probably no more than a standard 700 series with a switch in the bell circuit.
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Old 29th Oct 2009, 1:21 pm   #3
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Default Re: Another 700 series question

OK. Thanks for that. Learn something new every day. I've tried configuring it as a 706 w/bell switch. No luck. I'll just have to try harder!
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Old 29th Oct 2009, 1:43 pm   #4
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Default Re: Another 700 series question

Have a look here, go to the Document Repository (or whatever he calls it) and look up diagrams N806 and N808. You may then be able to determine if your instrument is indeed a 706 with switch 5A-3 fitted. That switch, by the way, is a single button which is locked by pressing one end and released by pressing the other end. Is that what you've got?
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Old 29th Oct 2009, 1:53 pm   #5
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Default Re: Another 700 series question

Remember that the bell is turned off by using the switch to place a short-circuit across it. Leave the switch disconnected when you first try the phone. One less thing to worry about.

The switch might also have been used to provide earth loop recall or shared service calling facilities.
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Old 29th Oct 2009, 2:31 pm   #6
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Default Re: Another 700 series question

Unless I'm more tired than I realised, I think that's how I've configured it. I have just noticed (and I'm no expert here) that there doesn't appear to be a regulator on board this instrument?
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Old 29th Oct 2009, 2:40 pm   #7
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Default Re: Another 700 series question

Hi,
If the phone is a 706 type it will have been fitted with a Switch 5A and a Locking button to provide the Bell On/Off facility.

To exploit the Bell on/Off facility when the telephone is wired for PST (Plug and Socket) working strap as follows -

Strap T16 - T17
T18 - T19
T5 - T6
Provide and fit a 3k3 0.5Watt resistor in place of strap T4 - T5; the phone may ring OK with strap T4 - T5 in place but if you intend to use extension telephones you may experience ringing problems if the resistor is not fitted.

Red of line cord to T8
White of Line cord to T18
Green of line Cord to T15 (Spare)
Blue of Line cord to T5

Slate (Grey) and Blue of Switch to T16
Brown of Switch to T18

If Bell On/Off is transposed in operation (i.e bell rings when switched off and vice versa) Swap Blue and Brown leads from Switch.

The N Diagram for a 706 telephone can be found Here and more information about 706 telephones can be found Here

Regards
Andrew
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Old 29th Oct 2009, 2:58 pm   #8
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Default Re: Another 700 series question

Quote:
Originally Posted by retrotelecom View Post
Unless I'm more tired than I realised, I think that's how I've configured it. I have just noticed (and I'm no expert here) that there doesn't appear to be a regulator on board this instrument?
Unusual! It seems to be half way between a 706 and 746 in its construction, with as you say, the regulator deleted
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Old 29th Oct 2009, 3:05 pm   #9
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Default Re: Another 700 series question

Yup! It sure is confusing the whatsit out of me. Not that that's too hard to do.
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Old 29th Oct 2009, 3:13 pm   #10
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Default Re: Another 700 series question

See here

No socket as far as I can see.

The case and chassis are 706-style, but the plastic caps and microswitch-style GS are much more reminiscent of a 746.

Nick.
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Old 29th Oct 2009, 7:06 pm   #11
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Default Re: Another 700 series question

Quote:
Originally Posted by retrotelecom View Post
Unless I'm more tired than I realised, I think that's how I've configured it. I have just noticed (and I'm no expert here) that there doesn't appear to be a regulator on board this instrument?
It'll be a PAX/PABX phone. Because they are only used in a local system they don't need a line current regulator, so it was omitted to save costs. Seems penny pinching, but in a large system of perhaps 200 - 500 phones it adds up. It'll probably work OK if you're not too far away from the exchange.

PS on some later phones with a plug-in regulator you can reverse it to bypass the regulator function.
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Old 29th Oct 2009, 7:09 pm   #12
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Default Re: Another 700 series question

Hi,
Looking at your picture you need to Transfer the Blue of the line cord from T15 to T5 (or T6), Currently the internal capacitor in the telephone is being used to ring the Bell and not the one in the master socket/Line Jack.

You also need to remove Strap T8 - T9; with Strap T8 - T9 in place you will have the telephones internal Ringing capacitor in parallel with the one in the Line Jack/Master Socket; Leaving T8 - T9 in place may cause Bell tinkle on your phone when dialing out on other extensions that use Pulse dialing.

You also Need to transfer the Green of the line cord from T17 to T15 - The Green wire is spare and only used for Earth Recall purposes (i.e. when attached to a PBX)

I have to agree with Nick that this phone looks a little like a Hybrid 706/746, however there were 706 models that had Printed circuit boards, the Gravity switch is very 746 esque though.

It is interesting to see that the board looks like it has never had a regulator fitted which suggests that the phones original setting may have been as a PBX extension or connected to a Local battery exchange (where the Battery for speech is fitted at the subscriber end and not at the Exchange) and later modified to include the dial.

On your picture I see that you have removed the Handset cord, presumably for clarity, for reference the handset cord connects White to T10, Red to T1, Green to T2, and Blue to T3.

Regards
Andrew
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Old 29th Oct 2009, 7:56 pm   #13
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Default Re: Another 700 series question

Well, thank you very much gentlemen. Silly old me .... andI thought I had bought a standard 706 just ripe for conversion. I think in future I will interrogate sellers for the numbers on the underside, and not just go on appearances!
I'm armed with screwdriver now to follow your instructions.
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Old 29th Oct 2009, 9:28 pm   #14
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Default Re: Another 700 series question

I think you've got a far more interesting phone than a standard 706, frankly, so don't be upset about it
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Old 29th Oct 2009, 9:46 pm   #15
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Default Re: Another 700 series question

You're quite right of course, and I'm not upset - just a little frustrated. I cannot get her to go. I've followed Andrew's wiring instructions to the letter. I have no dial tone. There's a bit of 'live' line noise in the earpiece, but no sidetone or any reaction from the transmitter (I've tried a couple of handsets). Operating the dial cuts off any life in the earpiece, and the bell-set doesn't function - irrispective of switch position or shorting the switch out. I don't want to push this one on you guys too much - if I'm out-staying my welcome on this one thread, please let me know.
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Old 29th Oct 2009, 10:15 pm   #16
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Default Re: Another 700 series question

No problem. Just post a good pic of how you've got it wired up at the moment and we'll see if anything looks amiss.

Nick.
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Old 29th Oct 2009, 10:38 pm   #17
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Default Re: Another 700 series question

latest effort!
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Old 29th Oct 2009, 11:00 pm   #18
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Default Re: Another 700 series question

Higher-res photo here:


http://picasaweb.google.co.uk/lh/pho...eat=directlink
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Old 29th Oct 2009, 11:02 pm   #19
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Default Re: Another 700 series question

Hi,
Take a look Here

Don't worry too much about the Bell not operating for the moment, we can help you on that one once you have managed to get the transmission side of things working.

As this phone uses a 746 type Hook switch with a 706 type cradle check the operation of the switch and cradle linkage, if the switch isn't operating correctly you can often be faced with some odd fault conditions.

Have you discovered the "Linesmans Latch yet? (Usually fitted somewhere on the Left Hand upright when looking at the phone with the dial facing you) this allows you to place the phone in "On Hook" condition, should you need to do so, whilst fault finding.

Andrew

Footnote - Try adding a Strap to T17 - T18 to see if that gets your Bell working

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Old 29th Oct 2009, 11:25 pm   #20
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Default Re: Another 700 series question

Hi,
I have discovered the 'linesman's latch' - I didn't know that was what it's called though. This 'phone doesn't have one!
The cradle seems to be operating ok, and the switch (when operated slowly) returns two clicks both on the way down and up again. Do I need to get the meter out on the board contacts to make sure it's actually doing what it should, electrically?
I've saved britishtelephones' fault finding sheet - that looks as though it will come in very handy in the future.

Doug
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