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Old 31st May 2022, 12:52 pm   #1
lachlan
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Default BT 746 - rotary dial does not retract and no dial tone

Hello all,
Recently bought an old 746 phone, and did the conversion for a modern line. However, there is no dial tone, and the rotary dial does not retract. Can anyone help me, or know of any specialists in Birmingham?
Thanks
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Old 31st May 2022, 12:57 pm   #2
Station X
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Default Re: BT 746 - rotary dial does not retract and no dial tone

If you "retract" the dial manually do you get dial tone then?
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Old 31st May 2022, 2:46 pm   #3
Dave Moll
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Default Re: BT 746 - rotary dial does not retract and no dial tone

Is it that you get no dial tone even with the dial in its rest position, or is the dial unable to return to this position? If the latter, this would explain the absence of dial tone as the transmitter and receiver are both shorted out while the dial is "off-normal" (i.e. away from its rest position).

Regarding the dial not returning, it would be worth opening up the 'phone and checking that there is nothing obstructing the dial mechanism (which may be enclosed in a plastic "cup" behind the dial).
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Old 1st Jun 2022, 1:26 pm   #4
dagskarlsen
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Default Re: BT 746 - rotary dial does not retract and no dial tone

The rotary dial has 5 wires, when the dial is moved out of the rest position 2 of these short out the receiver (loudspeaker) to eliminate noise. 2 of the 3 others shorts out the transmitter (microphone) to protect it from damage, The third is connected to the 2 others until the dial returns, when it returns it sends out small breakes (pulses) on the line to tell the exchange what number it dials, these pulses must be of a pretty accurate timing to work OK. A 0 gives 10 breakes of approx 67 milliseconds with approx 33 milliseconds between during a time of 1 second. when a 5 is only 5 of those pulses etc.

When the dial is in rest position you should have the dial tone.
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Old 4th Jun 2022, 8:48 pm   #5
winston_1
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Default Re: BT 746 - rotary dial does not retract and no dial tone

A non retracting dial is often caused by a broken spring.
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