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Old 28th Aug 2021, 11:58 am   #1
Electricawe
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Default GPO 332 converted but not ringing

Hi All,

I have recently converted an old GPO 332 to work with plug and socket. I have followed the instructions on this website: (https://antiquephones.blogspot.com/2...telephone.html), and it works, however, the ringing does not work. I have tried to put a wire between T10 and T12 as someone suggested, and I have also tried to clean the armature and tops of the bell coils, as another website suggested. It does sometimes try to ring, i.e. the armature moves a small amount upon first dialing the phone, but it will not ring after that. I did have it semi ringing, but then it stopped again. Not sure why that was?

I'm a bit stumped by this, any suggestions please?

Thank you.
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Old 1st Sep 2021, 9:14 pm   #2
crackle
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Default Re: GPO 332 converted but not ringing

I assume you have a master BT socket with ring capacitor.
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Old 2nd Sep 2021, 3:16 pm   #3
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Default Re: GPO 332 converted but not ringing

First thing those new to telephones/electronics should remember. A capacitor /condenser etc in a telephone has (usually) one function -block DC. With that in mind, the bell circuit( from hours of lectures at many GPO training schools ) was from line through a (usually 2/1.8uF capacitor) , through the bell coils and back to line.
If a bell tried to ring, I'd suspect a magnetised bell assembly and in my days as a GPO tech, I'd just change the phone.
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Old 2nd Sep 2021, 6:27 pm   #4
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Default Re: GPO 332 converted but not ringing

Thank you both for your reply. Yes, Mike, you are right, it's a BT NTE5 type.

Is there any way that I can test to see if it is in fact the bell coils causing the problems?

I'm guess that the capacitor within the phone no longer works, as it is 70 years old, but because I have the capacitor in the master socket it's not needed anyway?

Thank you.
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Old 2nd Sep 2021, 6:39 pm   #5
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Default Re: GPO 332 converted but not ringing

If it's "converted to work with plug and socket", the internal capacitor will have been disconnected as the expectation will be that the ringing current is coming from the capacitor in the master socket.

It is worth double-checking that the conversion has been done correctly according to the instructions at https://www.britishtelephones.com/pstconv1.htm#332.
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Old 4th Sep 2021, 12:06 pm   #6
Electricawe
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Default Re: GPO 332 converted but not ringing

Hi Dave,

I have checked on this website, and it is correctly wired inside the phone. So therefore the capacitor is not connected, which is good. What should the next troubleshooting step be?

Thanks.
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Old 4th Sep 2021, 2:27 pm   #7
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Default Re: GPO 332 converted but not ringing

Check the resistance across the bell coils (T2 & T12 according to diagram N432). The DC resistance should be about 1K.

If open-circuit, check between the soldered connections on the coils themselves, including between each end and the centre point where the coils are connected to each other. That should identify which coil has gone o/c.

If the resistance is correct, it means the ringing current isn't reaching the bell. Check the AC voltage between T2 and T12 (white and blue line cord wires respectively if the standard colours are in use) while the 'phone is being rung. If no pulses of current (in the ringing cadence) are present, it means the phone socket isn't delivering the ringing current and your investigations need to move to there.

If you wish to ignore the ringing current that is supposedly available from the socket, you can disconnect the ringing wire and reinstate the strap between T10 and T11 that was removed during the conversion. This will then use the internal capacitor instead of the one in the master socket.
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Old 4th Sep 2021, 5:07 pm   #8
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Default Re: GPO 332 converted but not ringing

Thanks Dave, It was o/c between T2 & T12, and as it turns out, the left bell coil as you would look at the phone if you opened it has a much higher resistance than the right one, the right one has the resistance of 500, which is correct but I had to switch to the 200k setting for the left one, which displays around 160 on the display, this cannot be correct? I have a 3K resistor in place, but this seems very high?

Thank you.
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Old 4th Sep 2021, 5:08 pm   #9
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Default Re: GPO 332 converted but not ringing

If I measure between T2 and T12 on the 200k setting, the reading bounces around, but is around 160 or so, any idea why it is throwing up this? That seems rather excessive?

Thanks.
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Old 4th Sep 2021, 6:48 pm   #10
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Default Re: GPO 332 converted but not ringing

As a quick test you could try shorting out the high-resistance coil and see whether you can obtain some sort of ringing from the one good coil, but it sounds as though the left coil is a-goner. Unless you have the facilities for rewinding coils, it sounds as though you will need to replace the bell motor.
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Old 5th Sep 2021, 8:37 am   #11
Electricawe
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Default Re: GPO 332 converted but not ringing

I will try that and let you know. That's a shame that the coil is finished. I wouldn't know how to rewind the coils, unfortunately, so I guess it's replacement time. I have looked around and can't seem to find one, where would I look at getting one of these please?
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Old 5th Sep 2021, 10:12 am   #12
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Default Re: GPO 332 converted but not ringing

I'll have a look this afternoon (not at home right now) and see whether I have a spare I could pop in the post to you.
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Old 5th Sep 2021, 6:57 pm   #13
Electricawe
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Default Re: GPO 332 converted but not ringing

Thank you. I did try shorting the other coil, but it didn't really work, unfortunately.
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Old 7th Sep 2021, 3:54 pm   #14
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Default Re: GPO 332 converted but not ringing

Quote:
Originally Posted by Dave Moll View Post
I'll have a look this afternoon (not at home right now) and see whether I have a spare I could pop in the post to you.
Apologies that I've only today managed to get round to checking my stores.

Although I have a few spare bell motors for 700 series, I only seem to have one 300 type one, and that also has one o/c coil. It should be possible to swap your o/c coil for the good one from mine as the coil is held in with a single nut, but you also have to remove the armature/clapper (by sliding out the pivot pin) to clear the path to remove or replace the coil. If you would like my good coil, PM me your address and I'll pop it in the post - no charge other than postage.
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Old 8th Sep 2021, 2:20 pm   #15
Electricawe
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Default Re: GPO 332 converted but not ringing

Thank you for the offer, but last night, I soldered a piece of wire to short the o/c coil, and it's working now! Must have been the fact that the joints were dirty and the metal I was shorting it with wasn't making good contact. Thank you for the advice though.

Thank you.
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Old 8th Sep 2021, 2:50 pm   #16
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Default Re: GPO 332 converted but not ringing

For temporary connections as you had before I have a few wires with a crocodile/alligator clip on each end. The teeth of the clip are quite good at biting into solder joints to bypass any surface oxidation.

Anyway, it's good to know that you have reasonably satisfactory ringing using only one coil.
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