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Vintage Telephony and Telecomms Vintage Telephones, Telephony and Telecomms Equipment |
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8th Jun 2012, 8:32 pm | #1 |
Retired Dormant Member
Join Date: Jun 2011
Location: Powys
Posts: 14
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Push Button 766 Trimphone Dialling Problem
Hi,
I've just wired up a GPO766 pushbutton Trimphone for plug and socket. It works except for that you can't dial out. When you press any of the pushbuttons the dialtone cuts out when it is pressed but then returns a second or so later. Any help or advice as to what may be causing the problem would be very much appreciated! Many thanks, Gavin |
8th Jun 2012, 9:45 pm | #2 |
Octode
Join Date: Jul 2011
Location: Stockport, Greater Manchester
Posts: 1,208
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Re: Push Button 766 Trimphone Dialling Problem
Possibly an obvious question but does your line actually support "pulse" dialling?
Robert |
8th Jun 2012, 9:50 pm | #3 |
Pentode
Join Date: Dec 2011
Location: Camelford, Cornwall, UK.
Posts: 188
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Re: Push Button 766 Trimphone Dialling Problem
Battery?
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8th Jun 2012, 10:06 pm | #4 |
Retired Dormant Member
Join Date: Jun 2011
Location: Powys
Posts: 14
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Re: Push Button 766 Trimphone Dialling Problem
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8th Jun 2012, 10:45 pm | #5 |
Octode
Join Date: Jul 2011
Location: Stockport, Greater Manchester
Posts: 1,208
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Re: Push Button 766 Trimphone Dialling Problem
I have one in pieces at the moment. Dial unit doesn't take a battery like the earlier units. It's a very complicated circuit, no doubt very advanced for it's time. Check the contacts under the buttons and for bad connections. There are 6 wires connecting mine to the main PCB, are all these connected OK?
Robert |
8th Jun 2012, 10:57 pm | #6 |
Dekatron
Join Date: May 2008
Location: Derby, UK.
Posts: 7,735
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Re: Push Button 766 Trimphone Dialling Problem
Try an analogue meter (on 50V DC range) across the line. The needle should flick up briefly in sympathy with the dialling pulses, if it is sending them.
__________________
If I have seen further than others, it is because I was standing on a pile of failed experiments. |
8th Jun 2012, 10:59 pm | #7 |
Retired Dormant Member
Join Date: Jun 2011
Location: Powys
Posts: 14
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Re: Push Button 766 Trimphone Dialling Problem
I seem to have just 5 on mine as below:
Brown - T3 Pink - T10 Orange - T8 Blue - T2 Grey - T1 This seems to correspond ok to the terminal numbers printed on the keypad PCB. But there are only these 5 connections. |
8th Jun 2012, 11:32 pm | #8 |
Octode
Join Date: Jul 2011
Location: Stockport, Greater Manchester
Posts: 1,208
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Re: Push Button 766 Trimphone Dialling Problem
There are several versions obviously! You could try a conventional dial "borrowed" from one of your 700 series phones to check the rest of the phone is working.
Robert |
12th Jun 2012, 11:24 pm | #9 |
Retired Dormant Member
Join Date: Mar 2012
Location: Milton Keynes
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Re: Push Button 766 Trimphone Dialling Problem
I have a similar problem with a 756 phone so I'll be watching this thread with interest.
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13th Jun 2012, 8:04 pm | #10 |
Dekatron
Join Date: Jan 2005
Location: Oxford, UK.
Posts: 17,820
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Re: Push Button 766 Trimphone Dialling Problem
Are we sure this is pulse dialling? I have (had?) some DTMF-only Trimphones somewhere, so they do exist. They were no doubt designed as PBX extensions as they predate the widespread introduction of DTMF dialling from subscribers' lines. They do work at home, but you have to hold down each button a little longer than you might normally to ensure that the exchange recognises the tone; quick, "staccato" dialling doesn't work reliably.
I also have a few of the DTMF 746-style phones of various vintages and models. At least one wouldn't dial out, and I'm afraid it was the DTMF generator chip (a Ferranti one, ISTR) which had failed. Impossible to obtain except by cannibalising another phone. N. Last edited by Nickthedentist; 13th Jun 2012 at 8:10 pm. |
13th Jun 2012, 9:44 pm | #12 |
Dekatron
Join Date: Jan 2005
Location: Oxford, UK.
Posts: 17,820
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Re: Push Button 766 Trimphone Dialling Problem
Thanks for the clarification, Dave.
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