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Old 9th Jun 2019, 3:41 pm   #31
TonyDuell
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Join Date: Jun 2015
Location: Biggin Hill, London, UK.
Posts: 5,190
Default Re: GPO planset with external extensions

Are you saying that when you press 'ext to exch' (and everything is on-hook), you get a DC voltage across the relay coil? Because I don't think you should. Try (temporarily) disconnectng the wires to the extensions at terminals 3 and 12 of the Block Terminal. Do you get that DC voltage across the relay (don't worry about the polarity for the moment) with no extensions connected? With just one extension connected (say the wite removed from terminal 3 but the one on terminal 12 in place)? With just the other extension connected?

The telephone line wires go to terminal 4 and 6 of the Block Terminal. Terminal 6 (the 'B wire') should be the -ve one. That is, your meter should read normally with the red probe on 4 and the black probe on 6
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