QUASAR CODES 3140 - DTMF Telephone Relay Switcher
5. If you are finding the unit is behaving erratically then you might wish to check that your phone line has
been wired with the correct polarity. The details for the typical BT home phone system are shown below.
Master Socket Schematic
Master Socket Wiring
Although pin 4 has no function in a domestic installation it is usually connected for
the sake of neatness. The quality of wiring carried out by many older BT wiremen is
often approaching art in its perfection.
The BT Drop Cable (The cable coming from the outside world)
This often has Orange, White, Green and Black wires. Usually (but not always)
Orange and White are the active pair and go to connections 2 and 5. In some master
boxes (such as the type with a removable front section) they go to two connectors
marked A and B. Which way around they are connected usually doesn't matter but
3140, some modems (especially older USA sourced ones) and some answering
machines
are
fussy about polarity, so it's wise if possible to check the voltage on the
line and connect -48V to the B leg (J2) and 0V to the A leg (J5).
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