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Old 17th May 2021, 3:36 pm   #1
Dave Moll
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Join Date: Feb 2005
Location: West Cumbria (CA13), UK
Posts: 6,118
Default Dialling problems with 232 and bellset 26

Yes, it's my turn to be stumped by a telephone that won't dial out, but otherwise works OK! Before you ask, yes the PABX which I am using to test it does accept loop disconnect dialling and is pretty laid back regarding dial speeds and make/break ratios.

For some reason, even without any connection (dial removed) between the dial-pulsing terminals (T3 and T4) there is a DC resistance between them of about 1,600Ω which appears to be sufficient to maintain a loop. In the receiver a dial tone (albeit somewhat reduced in volume) is audible, which is restored to normal volume by closing the contacts between T3 and T4.

Perhaps someone can spot an error in my wiring (see below and diagram N332).

Matters are slightly complicated by the incoming line cord from the BT plug using the following colour convention:
A leg = black
B leg = yellow
ring = red
... but it happened to be what I have to hand.

The wiring to the bellset is:
A leg (black) to B1 (one end of bell)
ring (red) to B2 (via B3 to other end of bell)
no connection to B4/B5 internal capacitor
no connection to B6 (middle of bell)
spare (green) to BE (no connection)
B leg (yellow) to B9 (spare - for onward connection to T1)
and between bellset and 232:
B3 to T2 (green)
B8 to T3 (white)
B9 to T1 (red)

I have used the standard red, white and green between bellset and telephone as I'm not constrained by the sequence of connections in a BT plug. It probably isn't clear from the image of the wiring in the 232, but the line connections are as above (T1 = red, T2 = green, T3 = white).
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