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Old 15th Nov 2017, 11:34 am   #41
bigus01
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Default Re: GPO 332 transmitter issue

Thanks for that, I have already tried 3 different ones.
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Old 15th Nov 2017, 11:38 am   #42
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Default Re: GPO 332 transmitter issue

Quote:
Originally Posted by bigus01 View Post
'This has the result of reversing the polarity in the handset...'
Don't worry about polarities in handsets. This is unimportant. The line polarity will change under certain circumstances anyway, and the T21A contains a bridge rectifier so it will work either way.

Can you confirm the following re: your handset wiring?

*That the common connection to both microphone and receiver is connected to terminal 5 on the telephone terminal block.

*That the connection unique to the receiver is connected to terminal 6 on the telephone terminal block.

*That the connection unique to the microphone is connected to terminal 4 on the telephone terminal block.

*That when the telephone is off-hook, there is no d.c. voltage (measure and say what it reads) across terminals 5 and 6 of the telephone terminal block.
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Old 15th Nov 2017, 11:48 am   #43
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Default Re: GPO 332 transmitter issue

In the handset I have M1 (green) strap to R2.
M2 (red)
R1 (white)
In the phone I have T4 (red)
T5 (green)
T6 (white)
There is a small voltage of about 2.5v across T5 & T6 with handset off the hook.
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Old 15th Nov 2017, 12:53 pm   #44
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Default Re: GPO 332 transmitter issue

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'There is a small voltage of about 2.5v across T5 & T6 with handset off the hook.'
There should be no d.c. voltage across the receiver. There's a couple of reasons why you may be seeing it.

Have you got another, more modern telephone plugged in elsewhere, or is there something else across the line you're using for your testing?

Can you disconnect your telephone from the line, disconnect the handset from the telephone terminal block and measure the resistance from terminal T1 of the dial terminal block to terminal T5 of the telephone terminal block? The only resistance you should measure is the 35 Ohms of the ASTIC winding.

With the handset disconnected and the carbon mic in place, can you measure the resistance of handset wires green - red and green - white?

Out of interest, can you see the numbered connections on the ASTIC (induction coil)?
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Old 15th Nov 2017, 1:19 pm   #45
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Default Re: GPO 332 transmitter issue

Resistance between T1 & T5 - 22 ohms
Resistance between green & red - 50 ohms
Resistance between green & white 45 ohms
There are no terminal markings visible on the coil. I do have another phone on an extension, which, if disconnected does drop the voltage slightly. Also connected are broadband router and Sky box.
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Old 15th Nov 2017, 2:00 pm   #46
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Default Re: GPO 332 transmitter issue

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Resistance between T1 & T5 - 22 ohms
This seems rather low. Even, with the phone 'off hook' and the 35 Ohm ASTIC winding shunted with the 1000 Ohm bell-coils in series with both non-inductive 30 Ohm windings and the 30 Ohm ASTIC winding will only give about 34 Ohms.

Could you repeat this measurement T1 dial strip to T5 telephone block with the phone 'on-hook', please?

Quote:
Originally Posted by bigus01 View Post
Resistance between green & red - 50 ohms
This seems low, so you must have one of the lower-resistance mic inserts: probably the one original to the 184 handset. The 164 handsets usually have a mic in that measures kilohms. It doesn't matter too much.

Quote:
Originally Posted by bigus01 View Post
Resistance between green & white 45 ohms
Sounds about right for a receiver 2P - one with the flat front once you've slid the diaphragm off.

Quote:
Originally Posted by bigus01 View Post
There are no terminal markings visible on the coil. I do have another phone on an extension, which, if disconnected does drop the voltage slightly. Also connected are broadband router and Sky box.
Wonder if there's something in either of these units that shunts the bell capacitor in the master LJU (main socket)? I wouldn't've thought so, mind. The terminals on the coil are tiny and a magnifying glass and good light helps!
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Old 15th Nov 2017, 2:08 pm   #47
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Default Re: GPO 332 transmitter issue

Measures the same 22 ohms.
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Old 15th Nov 2017, 2:57 pm   #48
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Default Re: GPO 332 transmitter issue

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Measures the same 22 ohms.
With the handset still disconnected, could you measure the resistance:-

Between terminals 5 and 6 on the telephone terminal block? Should be something like 105 Ohms on and off hook.

Between terminals 6 and 11 on the telephone terminal block? Should be something like 132 Ohms off hook and open-cct on hook. You may need to squeeze the switch-hook contacts together gently for this one: it will show you if they need cleaning!
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Old 15th Nov 2017, 3:03 pm   #49
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Default Re: GPO 332 transmitter issue

We ave readings of 90
105/ open circuit.
Regards

Just noticed my meter needed recalibrating, so shouldn't be far off the figures you suggest.

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Old 15th Nov 2017, 3:45 pm   #50
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Default Re: GPO 332 transmitter issue

Can you now reconnect the handset with the carbon mic insert in place, wires correct as you now have in post #43 and measure the on and off-hook resistance round the loop from terminal T8 on the telephone terminal block to terminal T1 on the telephone terminal block?

On-hook should be open-cct.

Off-hook should be about 84 Ohms with your particular carbon mic insert fitted. Again, you'll maybe need to squeeze the hook-switch contacts gently together.

Can you do this resistance measurement with the carbon mic insert removed as well? We're looking at open-circuit here.
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Old 15th Nov 2017, 4:16 pm   #51
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Default Re: GPO 332 transmitter issue

It is just under 80 ohms / open circuit both with and without mic.
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Old 15th Nov 2017, 4:46 pm   #52
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Default Re: GPO 332 transmitter issue

Hmmm... The loop should be open-circuit when the mic is removed. I'm thinking 'dodgy capacitor' now. But, before snipping the wires off (if you do this, either tape them up or sleeve them, and don't worry: the tele will work fine on a plug-and-socket arrangement without either cap) could you:-

Remove the mic and measure the resistance between terminal T5 on the telephone terminal block and terminal T4 on the dial terminal strip? Compare this with resistance measurement between terminals T5 and T4, both on the telephone terminal block. Should be the same: open-cct.
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Old 15th Nov 2017, 5:05 pm   #53
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Default Re: GPO 332 transmitter issue

No, 40 and 30 ohms respectively.
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Old 15th Nov 2017, 5:11 pm   #54
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Default Re: GPO 332 transmitter issue

Next thing is to check those dial-off-normal contacts again (don't worry that we're going round-and-round here).

Would you disconnect the dial at dial strip terminals T1, T2 and T3 and repeat the previous test as post #52 describes? What resistance do you measure now?
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Old 15th Nov 2017, 5:15 pm   #55
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Default Re: GPO 332 transmitter issue

Open circuits all round
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Old 15th Nov 2017, 5:35 pm   #56
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Default Re: GPO 332 transmitter issue

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Open circuits all round
It seems you need dial surgery! Your 'dial-off-normal' contacts should ONLY be closed when the dial is being rotated. Yours are closed and are shorting out the mic. Details on how to maintain dials are here.

As a final check, configure your telephone as a 'central battery' model (without a dial) by disconnecting the dial entirely and shorting together terminals T4 and T5 on the dial terminal strip.

Refit the carbon mic, plug the tele in and see if you can hear dial tone, and side-tone from blowing into the mic. If so, try your T21A mic again and see if that works similarly.
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Old 15th Nov 2017, 5:48 pm   #57
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Default Re: GPO 332 transmitter issue

The only contacts that are closed are the auxiliary ones, which (pulse) as dial is rotated.
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Old 15th Nov 2017, 6:00 pm   #58
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Default Re: GPO 332 transmitter issue

Would you still do the test, though? It seems odd that you get O/C with the dial off-normal contacts disconnected but a lowish resistance with them connected. Are you proving the contacts are open by sight or with a meter? It may be the wiring to the dial is iffy.
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Old 15th Nov 2017, 6:04 pm   #59
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Default Re: GPO 332 transmitter issue

Both visually and with a meter. You may see better on second photo. Wiring seems in good order.just a thought, is the dial strip wired correctly? Also, there is a connection across the bottom 2 capacitor terminals, is this of any relevance?
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Old 15th Nov 2017, 6:34 pm   #60
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Default Re: GPO 332 transmitter issue

Quote:
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'Also, there is a connection across the bottom 2 capacitor terminals, is this of any relevance?'
It could be (previous work). Remove all connections from the dial strip, connect terminals 4 and 5 on the dial strip together and give it a go. We'll try that first. If that cap connection is shorting the 0.1u cap out it needs removing.
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