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Old 17th May 2021, 2:36 pm   #1
Dave Moll
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Default Dialling problems with 232 and bellset 26

Yes, it's my turn to be stumped by a telephone that won't dial out, but otherwise works OK! Before you ask, yes the PABX which I am using to test it does accept loop disconnect dialling and is pretty laid back regarding dial speeds and make/break ratios.

For some reason, even without any connection (dial removed) between the dial-pulsing terminals (T3 and T4) there is a DC resistance between them of about 1,600Ω which appears to be sufficient to maintain a loop. In the receiver a dial tone (albeit somewhat reduced in volume) is audible, which is restored to normal volume by closing the contacts between T3 and T4.

Perhaps someone can spot an error in my wiring (see below and diagram N332).

Matters are slightly complicated by the incoming line cord from the BT plug using the following colour convention:
A leg = black
B leg = yellow
ring = red
... but it happened to be what I have to hand.

The wiring to the bellset is:
A leg (black) to B1 (one end of bell)
ring (red) to B2 (via B3 to other end of bell)
no connection to B4/B5 internal capacitor
no connection to B6 (middle of bell)
spare (green) to BE (no connection)
B leg (yellow) to B9 (spare - for onward connection to T1)
and between bellset and 232:
B3 to T2 (green)
B8 to T3 (white)
B9 to T1 (red)

I have used the standard red, white and green between bellset and telephone as I'm not constrained by the sequence of connections in a BT plug. It probably isn't clear from the image of the wiring in the 232, but the line connections are as above (T1 = red, T2 = green, T3 = white).
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Old 18th May 2021, 8:29 am   #2
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Default Re: Dialling problems with 232 and bellset 26

Quote:
Originally Posted by Dave Moll View Post

For some reason, even without any connection (dial removed) between the dial-pulsing terminals (T3 and T4) there is a DC resistance between them of about 1,600Ω
Are you seeing this resistance without the bellset connected to the telephone, Dave?
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Old 18th May 2021, 8:35 am   #3
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Default Re: Dialling problems with 232 and bellset 26

No.
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Old 18th May 2021, 8:49 am   #4
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Default Re: Dialling problems with 232 and bellset 26

Further to the above rather terse response, I had realised that the DC path was through the bell coils and the inductance coil - and that I can probably circumvent the problem by connecting the bell via its internal capacitor and the telephone via the one in the master socket - but I would like to solve the problem rather than side-step it!
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Old 18th May 2021, 8:54 am   #5
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Default Re: Dialling problems with 232 and bellset 26

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Originally Posted by Dave Moll View Post
No.
Why do you need a connection between the bellset and terminal T3 on the telephone? Unless you're connecting it as an original installation, of course, with the internal capacitor connected. But I see you're not, reading your post.

I would be inclined to disconnect your bellset from the telephone and measure out the terminals there (including the lead between telephone and bellset).

It looks like with your telephone connected, you are measuring round the loop of carbon mic > 35 Ohm ASTIC winding > down the connecting wire to your bell in the bellset then back up the connecting wire back to T3 on your telephone.

I know this is a 332 instrument and the connections are labelled differently and the bell is contained within the instrument, but surely it's similar otherwise? Would this help? Using your own colours, natch.
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Old 18th May 2021, 9:05 am   #6
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Default Re: Dialling problems with 232 and bellset 26

Quote:
Originally Posted by russell_w_b View Post
Why do you need a connection between the bellset and terminal T3 on the telephone?
Do you mean T2 (green)? T3 is the A leg (white), without which the telephone will receive no signal. Isn't the T2 connection also needed for the speech circuit?

Quote:
Originally Posted by russell_w_b View Post
It looks like with your telephone connected, you are measuring round the loop of carbon mic > 35 Ohm ASTIC winding > down the connecting wire to your bell in the bellset then back up the connecting wire back to T3 on your telephone.
That's the conclusion I reached too.

By the way, what is the electrical difference between your diagram and how my setup is wired?
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Old 18th May 2021, 9:19 am   #7
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Default Re: Dialling problems with 232 and bellset 26

Does it work right if you use T1-B1, T2-B2 and T3-B4 ?

That way you get the 2 uF cap between T2 and T1, that works as a part of the anti-sidetone circuit, and as a capacitor for the ringer as in the old days.

If you use the typical UK system with master socket and no ringer capacitor in the phone you have to change the ringer-capacitor connection.

In my Norwegian setup the only needed line wires will be T1 and T3

dsk

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Old 18th May 2021, 9:49 am   #8
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Default Re: Dialling problems with 232 and bellset 26

Quote:
Originally Posted by Dave Moll View Post

Do you mean T2 (green)? T3 is the A leg (white), without which the telephone will receive no signal. Isn't the T2 connection also needed for the speech circuit?
Ah... See what you mean now - you're leading the plug into the telephone via the bellset. But is the terminal on which T3 connected to the bell in any way? It shouldn't be. It should go straight to the telephone speech cct.


Quote:
Originally Posted by Dave Moll View Post
By the way, what is the electrical difference between your diagram and how my setup is wired?
I haven't drawn yours out yet to see. I shall do, though! there shouldn't be any difference, really, all being well. Just on with another job at the mo so can't give it my full attention just yet. Try separating phone and bell and see if your resistance measurements stack up to what you expect to see on the bellset. But 1600 Ohms sounds suspiciously like a pair of bell-bobbins to me, plus carbon mic and ASTIC winding.
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Old 18th May 2021, 11:28 am   #9
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Default Re: Dialling problems with 232 and bellset 26

Quote:
Originally Posted by russell_w_b View Post
Ah... See what you mean now - you're leading the plug into the telephone via the bellset.
As per the approriate N diagram except that I'm using the master socket capacitor rather than that in the BS26

Quote:
Originally Posted by russell_w_b View Post
But is the terminal on which T3 connected to the bell in any way? It shouldn't be. It should go straight to the telephone speech cct.
It goes both to the telephone and the "earthy" end of the bell - otherwise there would be no return path for the ringing current from the "ringing" wire. T1 (red, B leg) is not connected to the bell. It uses B9 (no internal connection) as a means to pass this to the telephone.


Quote:
Originally Posted by russell_w_b View Post
1600 Ohms sounds suspiciously like a pair of bell-bobbins to me, plus carbon mic and ASTIC winding.
I have little doubt that this is correct. It may be that this was a red herring, but I am still left with the conundrum that opening the pulsing contacts doesn't break the loop (as needed by LD dialling).
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Old 18th May 2021, 12:07 pm   #10
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Default Re: Dialling problems with 232 and bellset 26

Quote:
Originally Posted by Dave Moll View Post
It goes both to the telephone and the "earthy" end of the bell - otherwise there would be no return path for the ringing current from the "ringing" wire. T1 (red, B leg) is not connected to the bell. It uses B9 (no internal connection) as a means to pass this to the telephone.


On the paster diagram, terminal T1 is the 'earthy' end of the bell and the ringing wire should go to T2, yes?

If you look at drawings for a 300 and 700 series instruments, the 'earthy' end of the bell is in the cradle-switch / ASTIC / mic side and not in the LD pulse contact side. Have you tried swapping over A & B (ie: pins 2 and 5 on the plug) and leaving the ringing wire as-is?
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Old 18th May 2021, 1:43 pm   #11
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Default Re: Dialling problems with 232 and bellset 26

As the paster diagram is the bell, I have used Bn numbers therein, reserving Tn for the telephone, so yes, B1 is the earthy end.

Although swapping A and B on the way into the bell resulted in the bell not working, as the ringing current was between black and red, this does give me an idea - I will try swapping red and white between the bell and the telephone. This would have the effect of placing the A leg on the cradle-switch side and the B leg on the LD side as you have suggested.
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Old 19th May 2021, 11:22 am   #12
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Default Re: Dialling problems with 232 and bellset 26

The colors here is pretty random, but this shall work!
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Old 19th May 2021, 6:48 pm   #13
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Default Re: Dialling problems with 232 and bellset 26

Your first diagram appears to have only one bell coil in circuit, but moving your green (conventionally white) wire from 6 to 7, 8 or 1, I agree should work (i.e. using the capacitor in the bellset rather than that in the master socket). As Russell has intimated, it seems that my confusion has stemmed from the wire colours shown in the N-diagram appearing to equate to red for A leg and white for B leg, so swapping these while still using the master socket capacitor should also work.

Unfortunately, my experiments have gone on hold at present as both cables involved have developed o/c wires, so I need to source some replacements (preferably with conventional colouring to be less confusing) before continuing.
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Old 20th May 2021, 5:15 am   #14
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Default Re: Dialling problems with 232 and bellset 26

Yes, you are right, should ofcourse use both coils.

Editid the drawing now.

Maybe you have a leak in the circuit, a bad capacitor, or moist terminal wood strip?

If you just connect the bellset, but not the phone, how does it work?
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Old 20th May 2021, 8:22 am   #15
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Default Re: Dialling problems with 232 and bellset 26

I have now found some reliable cables, and as implied above, the problem was that I had A leg and B leg transposed. I shouldn't have assumed that red = B leg and white = A leg. Connections to the 232 are:

T1 (red): A leg
T2 (green): "ring" wire
T3 (white): B leg

Wired this way, everything (including dialling out) works correctly. Thank you to everyone (especially Russell) for the assistance.
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Old 20th May 2021, 10:39 am   #16
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Default Re: Dialling problems with 232 and bellset 26

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I have now found some reliable cables...
Pleased you got sorted, Dave. Were you using that tinselly-type cable with the nylon wormings in it? I've had that go O/C on the plug before now.
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Old 20th May 2021, 11:09 am   #17
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Default Re: Dialling problems with 232 and bellset 26

It was modern cable with the very thin wires, and it transpired that these were not making good contact with the crimped terminals. A dob of solder seems to have fixed them, but they've now been replaced now anyway.
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Old 20th May 2021, 12:14 pm   #18
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Default Re: Dialling problems with 232 and bellset 26

Good to hear!
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