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Old 17th Aug 2012, 4:49 pm   #21
Station X
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Default Re: Struggling to convert GPO 706.

That resistor certainly shoudn't be there. As I said before it's probably a bodge to get round a fault on the PCB.

Have you cleaned off ALL the corrosion yet? Until you've done that you're wasting your time trying to carry out any form of fault finding.
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Old 17th Aug 2012, 5:03 pm   #22
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Default Re: Struggling to convert GPO 706.

Yes I agree with that because without the resistor the phone is totally dead, so must be to cover some sort of fault.
I've scraped all the corrosion off as good as I can get it, not sure where to go with it now! Seems to almost be working but not quite right.
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Old 17th Aug 2012, 5:11 pm   #23
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Default Re: Struggling to convert GPO 706.

Quote:
Originally Posted by Station X View Post
That resistor certainly shoudn't be there. As I said before it's probably a bodge to get round a fault on the PCB.
Unless it was a way of manually tweaking the sensitivity of transmission/reception or the amount of sidetone, on-site, i.e. in place of the usual regulator.

Nick.
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Old 17th Aug 2012, 5:15 pm   #24
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Default Re: Struggling to convert GPO 706.

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I've scraped all the corrosion off as good as I can get it, not sure where to go with it now!
You need to get a meter or test bell/buzzer. Plenty of people here can tell you what tests to make.

I note Nick's comments, but side tone has nothing to do with the ability to sieze the line, dial out and trip incoming ringing.
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Old 17th Aug 2012, 5:34 pm   #25
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Default Re: Struggling to convert GPO 706.

One thing you can try is short-circuiting the transmitter (microphone) to eliminate it from you enquiries. Simply connect both wires to it to one of its terminals.

Then see if you can get dial tone, dial out and trip ringing.
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Old 17th Aug 2012, 8:48 pm   #26
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Default Re: Struggling to convert GPO 706.

ive tried to different handsets and both the same so pretty sure its not the mic.

Ive removed the original resistor between 1 and 10 and wired it up the standard way minus the resistor. With no resistor fitted at all the phone still rings.

So it seems it does not need a resistor. However the handset only answers the call when it has a connection between 1 and 10.

Therefore I need to find a way of making it stop ringing in an alternative way to linking 1 and 10 because although this operates the answer call properly, the volum is low as explained before and the caller cant hear on the other end of the line

Stumped!!!
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Old 17th Aug 2012, 9:38 pm   #27
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Default Re: Struggling to convert GPO 706.

You need to check the continuity of the calling loop. If it's OK, there's no reason why ringing shouldn't be tripped on answer.

With reference to the diagram linked to in post #3, the calling loop is as follows:-

White of line cord.
T18
T19
(via PCB track)
Switch hook 5
Switch hook 4

I'm guessing the next bit.

(via PCB track)
Induction coil 4
Induction coil 5
(via PCB track)

End of guessing

T3
Blue of handset cord
Mic
White of handset cord
T10
Pink wire.
Dial spring 4
Dial Spring 5
Orange wire
T8
Red of line cord.
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Old 17th Aug 2012, 9:46 pm   #28
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Default Re: Struggling to convert GPO 706.

Looking at your pictures I'd say the PCB link from T19 to the hook switch looks pretty dodgy.
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Old 17th Aug 2012, 9:54 pm   #29
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Default Re: Struggling to convert GPO 706.

I've come to the conclusion that this phone is a 706 without a regulator and having a "mechanically" different bell. What were connections B, C and D of the non-existent regulator will be connected together.

It should convert exactly as per a 706, but could be loud on a short line.

I reckon your problems are down to corrosion which may have affected switch hook and dial contacts as well as the PCB tracks.
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Old 17th Aug 2012, 9:58 pm   #30
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Default Re: Struggling to convert GPO 706.

Cheers guys, I guess I will just have to keep this one for show! Thanks for all the help and your time.
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Old 17th Aug 2012, 10:04 pm   #31
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Default Re: Struggling to convert GPO 706.

Hi,
The phone looks like and Ericsson N1900 or similar, which would have been used on a PAX, as previously suggested.

The additional resistor would have been to reduce the excessive sidetone on a short line so may not be required depending on how far away you are from the exchange.

There's no reason why the phone shouldn't work if wired in the same way as a 706 or 746, if bell tinkle is experienced this may be either due to ADSL filters elsewhere on the line or Strap T7-T8 and/or T6-T7 being present.

As has already been suggested the damage on the pcb needs investigating before going any further.

Regards

Andrew
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Old 17th Aug 2012, 10:05 pm   #32
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Default Re: Struggling to convert GPO 706.

Quote:
I guess I will just have to keep this one for show!
Why? Just bridge any broken tracks by soldering a wire across the gap and clean any dirty switch contacts.

Only an open circuit induction coil (an unlikely event) will be fatal.
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Old 17th Aug 2012, 10:16 pm   #33
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Default Re: Struggling to convert GPO 706.

like I say my electrical knowledge is minimal so wouldnt really know how to repair any broken tracks!

The only problem seems to be no volume from the mic on the other end of the call and the speaker volume a bit low. What would be the best way to start tackling this particular fault?

Cheers
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Old 17th Aug 2012, 10:17 pm   #34
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Default Re: Struggling to convert GPO 706.

Quote:
Originally Posted by AndiiT View Post
There's no reason why the phone shouldn't work if wired in the same way as a 706 or 746, if bell tinkle is experienced this may be either due to ADSL filters elsewhere on the line or Strap T7-T8 and/or T6-T7 being present.
Non of the straps mentioned are present and the ADSL filter is removed, so I guess its most likely the PCB damage is the cause.
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Old 17th Aug 2012, 10:48 pm   #35
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Default Re: Struggling to convert GPO 706.

Quote:
What would be the best way to start tackling this particular fault?
See post #28. At least try relating the crcuit diagram to the phone you have in front of you. If you don't have a meter, inspect the tracks and contacts visually, possibly with the aid of a magnifying glass.

These phones are really very simple bits of kit.
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Old 18th Aug 2012, 12:21 am   #36
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Default Re: Struggling to convert GPO 706.

Hello,

I'm no expert on telephones, but looking at the pictures of the phone it has links joining terminals 4, 5 and 6 together; 8 and 9 together and 16, 17, 18, and 19 together wheras looking at the circuit diagram, for normal use should it not have links joining terminals 4,5,6 and 7 together; terminals 8 and 9 together; terminals 16 and 17 together and terminals 18 and 19 together?

Yours, Richard
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Old 18th Aug 2012, 7:21 am   #37
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Default Re: Struggling to convert GPO 706.

The diagram shows a "hardwired" phone. This is how it would have been used prior to the advent of the current plug and socket system. The line cord would have been directly connected to the exchange line pair.

The pictures show the phone as converted for use with a plug and socket system. This disconnects the bell capacitor in the phone, as this capacitor is now located in the master jack.

No matter how the phone is wired, I fear that it will not work correctly as it obviously has faults which need attention.

In another life, about 45 years, ago I used to repair and install these phones. All faults on them can be located by simple continuity testing, or at a push visual inspection.
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Old 18th Aug 2012, 11:14 am   #38
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Default Re: Struggling to convert GPO 706.

I managed to solder a wire between 1 of the broken tracks ( pretty advanced stuff for me) the one you said looked badly corroded but still no joy. However the terminal which you say is for the mic does not have any track running from it? Is this the only place this wire can be connected?

Cheers
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Old 18th Aug 2012, 12:46 pm   #39
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Default Re: Struggling to convert GPO 706.

I assume you mean T3? In a 706 this would connect to the regulator and hence to the induction coil. T11, which would be spare in a 706, looks like it's connected to the induction coil. Try connecting the blue wire there.
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Old 18th Aug 2012, 1:00 pm   #40
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Default Re: Struggling to convert GPO 706.

If no joy, try reverse engineering the PCB to see how it differs from diagram N806. I don't have time to do it right now, but perhaps another member could do it from the pictures?
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