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Old 19th Aug 2012, 9:46 am   #41
Station X
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Default Re: Struggling to convert GPO 706.

I reversed engineered this phone from the pictures. It is wired in the same way as a 706, except for the connections to the induction coil.

The following connections to the induction coil are the same as those for a 706:-

IC2 is connected to the common point of the resistors R1 and R2.
IC3 is connected to T1.
IC4 is connected to switch hook contact 4.

The following connections differ from a 706:-

IC1. There is no IC1
IC5 (a guess as to terminal designation) is connected to T11.

I am assuming that there is a winding between IC4 and IC5

I suggest restoring the blue wire of the handset cord to T3 and running a wire from T3 to T11.
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Old 23rd Aug 2012, 11:11 pm   #42
JohnBHanson
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Default Re: Struggling to convert GPO 706.

Worth checking that you have the microphone wires connected correctly - white to T10, blue to T3. If that does not work try connecting the resistor across the microphone or measuring the voltage accross the microphone.
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Old 23rd Aug 2012, 11:19 pm   #43
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Default Re: Struggling to convert GPO 706.

There's no PCB track from T3 of this phone. The wire from D3 is connected to it, but there's no connection to the transmission circuit. Hence my suggestion to connect T3 to T11.
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