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Old 5th Jun 2019, 6:41 pm   #13
Join Date: Jun 2015
Location: Biggin Hill, London, UK.
Posts: 3,819
Default Re: GPO planset with external extensions

OK, I think it's time to go through this logically. I am working from the diagrams on pages 6 and 7 of N4507 (from Sam's site).

Now we have Exch-to-Extn operated, so contact KE5 is open, disconnecting the 'main unit' bell. KE1 is changed over, so the B wire (terminal 4 in the main unit) goes out on terminal 1 to the relay coil in the ringing converter. Contact A2 (part of the relay inside the plinth) should be open as relay A is not energised, so the relay coil is not shorted out. The other side of the relay coil comes back on terminal 9, then via KA1 or KB1 (both not operated) to the bells in the extensions, then to earth (and thus back to the A wire which is assumed to be earthed at the exchange)

The relay in the ringing converter has one contact. This conects the +v side of the PSU to one side of the buzzer, the other side of the buzzer goes to the -ve side of the PSU via contact A3.

OK. Now I believe you said the extensions do ring in this mode So there must be a path from the B wire to the appropriate line of the extension, the to 'earth' and back to the A wire.

So there seem to be several possibilites :

1) Contact A2 is closed for some reason, shorting out the relay coil

2) The relay in the ringing converter is not operating for some reason.

3) Contact A3 is open for some reason

4) The buzzer is faulty

5) The PSU is defective.

Start by taking the cover off the ringing converter. The relay is obvious. Now have an incoming call. Does it operate? If not then either relay A is operated for some reaso or the wiring is wrong.

Maybe the line current sense reed relay LS has stuck closed? That would cause A to be energised.
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