GPO 1/232 suddenly stopped hanging up

[shawthing]

Hello all, can anyone help please with a new problem on a restored & rewired GPO 1/232 - it's suddenly no longer able to hang up, after 3 or 4 years of faultless use on a BT line, via an extension socket with ADSL filter and one other modern touchtone phone on another extension, neither phone directly plugged into the master socket. I have opened it and checked that the black plastic end part of the plunger is still intact and that it does separate the leaves of the switch springs when the receiver is on hook (I've read up and studied the pics at the britishtelephones site). I've also tried holding the spring leaves apart with an insulated tool, and the phone continues to be connected to the line even with those spring contacts apart. I've also removed the ADSL filter (no change) and plugged the 232 directly into the BT master socket (again, no change).
It's not quite been an instantaneous problem: a few weeks ago the phone, while not in use and on the hook, suddenly began emitting the siren noise that the exchange sends when you leave it off the hook. I was out, my wife assumed there was problem on the line and disconnected the phone for a few hours, and it's been fine ever since... until last night, when again, out of the blue while not in use it suddenly started doing the same thing. Jiggling the plunger (automatic reaction) ends up triggering the 'Please replace the receiver and try again message' because it thinks you're trying to dial out.
There is currently no way to disconnect from the line, other than unplugging from the socket.
I'm wondering whether a cap or resistor somewhere has gone off spec or failed entirely, but I can't actually see anyone components inside the phone and my knowledge of phone connections is pretty poor. The phone was bought from a vintage phone dealer and had been rewired for modern BT use and has indeed worked perfectly until now, so if anyone could point me in the right direction I'd be very grateful - hugely missing the beautiful real ring!
Thank you in advance and apologies for the long post, but I wanted to include all the info I could think of, Chas

[russell_w_b]

Can you put a multimeter on 'Ohms' across pins 2 and 5 of the BT plug at the end of the lead (with it disconnected from the socket) and tell us what it reads on-and-off-hook?

[shawthing]

Hello Russell, thank you for the reply: it initially reads 4.32M and climbs slowly to 4.66M, where it holds. It's the same on or off the hook, tested several times on and off, to be sure.
Chas

[julie_m]

4.66 MΩ ?! You have a very good meter for measuring high resistances! As far as telephones go, anything over a few tens of kΩ is an open circuit.

The fact of the resistance not changing when the hook switch is operated sounds as though the hook switch contacts are dirty, not closing properly, or there is a poor connection between the line cord and the hook switch. Open the phone up and apply your probes right onto the switch itself, and operate a few times. If all seems normal, move one of the probes one piece of wire further away from the switch, and operate again. Keep repeating this process until you find the bad connection.

[Dave Moll]

At that sort of resistance surely it would fail to make a loop rather than fail to hang up.

[shawthing]

Thanks Julie, I will try this. I've tried cleaning the switch contacts (fine emery and contact cleaner) and each side seems to make contact properly, so I guess the problem must be further on. Best done in daylight, I think, Chas

[russell_w_b]

4.66 Megohms sounds like fingers to me.

I'm presuming, perhaps incorrectly, that your 232 tele looks like this, which you may find helpful. The only discrete resistor might be the 3k3 in series with the bell bobbins.

Do as Julie says, or start at the pin-end and work your way back up the lead. One cradle-switch set makes the loop, the other set shunts the dial pulse contacts via the cap in the master box and the resistance wound on the induction coil, so preventing 'tinkle-bell' when you dial.

White 'A' goes to pin 2 of your BT plug; red 'B' to pin 5. Blue to pin 4. Your colours may be different.

[dagskarlsen]

Originally Posted by shawthing

Hello all, can anyone help please with a new problem on a restored & rewired GPO 1/232 - it's suddenly no longer able to hang up, after 3 or 4 years of faultless use on a BT line, via an extension socket with ADSL filter and one other modern touchtone phone on another extension, neither phone directly plugged into the master socket. I have opened it and checked that the black plastic end part of the plunger is still intact and that it does separate the leaves of the switch springs when the receiver is on hook (I've read up and studied the pics at the britishtelephones site). I've also tried holding the spring leaves apart with an insulated tool, and the phone continues to be connected to the line even with those spring contacts apart. I've also removed the ADSL filter (no change) and plugged the 232 directly into the BT master socket (again, no change).
It's not quite been an instantaneous problem: a few weeks ago the phone, while not in use and on the hook, suddenly began emitting the siren noise that the exchange sends when you leave it off the hook. I was out, my wife assumed there was problem on the line and disconnected the phone for a few hours, and it's been fine ever since... until last night, when again, out of the blue while not in use it suddenly started doing the same thing. Jiggling the plunger (automatic reaction) ends up triggering the 'Please replace the receiver and try again message' because it thinks you're trying to dial out.
There is currently no way to disconnect from the line, other than unplugging from the socket.
I'm wondering whether a cap or resistor somewhere has gone off spec or failed entirely, but I can't actually see anyone components inside the phone and my knowledge of phone connections is pretty poor. The phone was bought from a vintage phone dealer and had been rewired for modern BT use and has indeed worked perfectly until now, so if anyone could point me in the right direction I'd be very grateful - hugely missing the beautiful real ring!
Thank you in advance and apologies for the long post, but I wanted to include all the info I could think of, Chas

Back to the beginning, you got the howling, that indicates OK contacts all up to the phone, so what's not happening is the break of the circuit when going on hook? Why? The switch hooks may have been bent, maybe some dirt in the mechanism stopping the fork moving all the way, or may be a shorted capacitor' doing it? I do not know the 232, but its unlikely the capacitor so I would start with the switch hooks and related mechanics.

Good luck from Norway

dsk

[Station X]

I'd have said it was a problem with the switch hooks, but it's at odds with the OP's statement that he sees around 4Mohm resistance looking into the phone regardless of whether it's on hook or off hook.

[shawthing]

Thanks all - problem is solved, and it was indeed the switch contacts! Although I'd cleaned them, I did it without dismantling and clearly there was something there I didn't see. I initially followed Julie's advice but all the wiring was fine so I too thought it must be the switch. Also, this phone has been rewired for modern use, with an internal bell added, so it doesn't in fact look like the diagram Russell - in fact only one side of the switch is used at all. Anyway, quite odd: I couldn't see anything wrong with the switch at all, but dismantling, cleaning and re-assembling... and bingo, back again!
So pleased - it's such a lovely phone, also would highly recommend anyone using this sort of vintage of phone to upgrade the microphone (easily available on Ebay). Before we did that everyone said they could hardly hear us, huge improvement!
Thanks again everyone, best regards, Chas