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Old 16th May 2017, 2:57 pm   #1
davidm123
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Default GPO Telephone 741 conversion.

Hi.

I have got a 741 Wall mount phone and am trying to convert it. I bought a conversion kit and I have followed all instructions that came with the kit.

All I can get the phone to do is ring and I can answer it and talk and l can listen, but I get no dialing tone and I cannot ring out. I wondered if anyone might be able to help me in some way.

Thank you.
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Old 16th May 2017, 3:11 pm   #2
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Default Re: GPO Telephone 741 conversion.

Quote:
Originally Posted by davidm123 View Post
I can answer it and talk and l can listen, but I get no dialing tone
Are you saying that you can have a two way conversation, yet cannot hear dial tone? Or that there's no reception at all?
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Old 16th May 2017, 3:21 pm   #3
Dave Moll
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Default Re: GPO Telephone 741 conversion.

What you describe implies that it makes a loop (goes "off hook") when you lift the handset in response to an incoming call, yet fails to do so when attempting to initiate an outgoing call. I cannot immediately think of a way to make a telephone do that!

Is there any chance of an image of your wiring? This would give an opportunity to double-check the connections and see whether you have overlooked anything.
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Old 16th May 2017, 3:49 pm   #4
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Default Re: GPO Telephone 741 conversion.

Hi. I'll try and take a photo and upload it in a few minutes.
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Old 16th May 2017, 4:06 pm   #5
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Default Re: GPO Telephone 741 conversion.

Hi. Here are some photos sorry they are not too good, it just looks like a mass of wires but I have tried my best.
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Old 16th May 2017, 4:21 pm   #6
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Default Re: GPO Telephone 741 conversion.

May I suggest that you remove the link between T6 and T7. It may not solve your problem, but what you have does mean that you have the internal capacitor connected in parallel with the one in your master socket.
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Old 16th May 2017, 4:26 pm   #7
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Default Re: GPO Telephone 741 conversion.

OK I' ll do that but does every other wire and strap look OK?
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Old 16th May 2017, 4:26 pm   #8
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Default Re: GPO Telephone 741 conversion.

I can't quite see what's going on around T1 and T2. Is there a short circuit there?

Have you got two rectifiers fitted in parallel? ie a red one and a black one? You only need one. Tidy up that area.
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Old 16th May 2017, 4:29 pm   #9
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Default Re: GPO Telephone 741 conversion.

I'll take a better photo please stand by thank you.
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Old 16th May 2017, 4:31 pm   #10
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Default Re: GPO Telephone 741 conversion.

Could well be, Graham. It also seems to have both a proper and ersatz Rectifier 205.
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Old 16th May 2017, 4:33 pm   #11
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Default Re: GPO Telephone 741 conversion.

Quote:
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I'll take a better photo please stand by thank you.
No need for that. A visual inspection should tell you whether the tags are shorted or not. A short would be entirely consistent with the symptoms as I understand them.

The tag on the green wire of the handset cord appears to be touching the tag of the red rectifier.
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Old 16th May 2017, 4:35 pm   #12
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Default Re: GPO Telephone 741 conversion.

Now that you mention it, there do appear to be two rectifiers in parallel - I suggest you keep one as a spare for any future use. I think that area looks otherwise OK, with the receiver between T1 and T2, and the transmitter between T3 and T10.

I can't offhand spot anything else amiss. Once both of these corrections are made, do you still have the same problem?
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Old 16th May 2017, 4:39 pm   #13
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Default Re: GPO Telephone 741 conversion.

Quote:
Originally Posted by Station X View Post
The tag on the green wire of the handset cord appears to be touching the tag of the red rectifier.
Though, of course, this may be simply a matter of line-of-sight with a separation in the vertical axis. Adding separation in the horizontal axis as well is, however, good practice!

Quote:
Originally Posted by Station X View Post
A short would be entirely consistent with the symptoms as I understand them.
Surely, a short would simply result in little or no sound in the receiver, whereas the OP states ability to talk and listen on answer.
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Old 16th May 2017, 4:42 pm   #14
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Default Re: GPO Telephone 741 conversion.

If they're not touching, it's only the width of a gnat's pyjama cord separating them.
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Old 16th May 2017, 4:45 pm   #15
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Default Re: GPO Telephone 741 conversion.

Hi I have taken off the connection between T6-T7 then i tested the phone again and it now won't ring or dial tone or dial out But I can answer a call OK and talk and listen. Also I took photos of T1-2 as best as I can.
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Old 16th May 2017, 4:48 pm   #16
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Default Re: GPO Telephone 741 conversion.

Remove the red rectifier and slew the green lead round 45 degrees clockwise. Then we can be certain there's no problem or likely future problem in that area.
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Old 16th May 2017, 4:49 pm   #17
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Default Re: GPO Telephone 741 conversion.

I see that the two rectifiers are still in place. If you remove the red one, the problem of the possible short will go away if nothing else!

edit: Station X beat me to it.
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Old 16th May 2017, 4:51 pm   #18
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Default Re: GPO Telephone 741 conversion.

do you mean remove this
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Old 16th May 2017, 4:51 pm   #19
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Default Re: GPO Telephone 741 conversion.

Yes indeedy!
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Old 16th May 2017, 4:53 pm   #20
davidm123
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Default Re: GPO Telephone 741 conversion.

ok ill do that see you in a min but why now has it stooped ringing
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