AT&T System 25 - Manual (Page 176)

SYSTEM TESTS
TEST TOUCH-TONE RECEIVERS
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At a single-line voice terminal, go off-hook. Dial *3 and the 2-digit
number (01 through 12) of the touch-tone receiver to be tested.
Receivers 01 through 04 are on the ZTN85 or ZTN131 (R3) CP.
Receivers 05 through 12 are only present if your system has two
TN748 CPs (05 through 08 receivers on one, and 09 through 12
receivers on the other).
You will hear busy tone if the receiver is in use, reorder tone
if you misdialed or addressed a receiver not in your system
(for example, you dialed *O5 and your system does not have
a TN748 CP). Try again.
If you hear dial tone after 1 to 3 seconds of silence, proceed
with this test.
DiaI the digits 1234567890 *#.
Repeat
You should hear a dual-tone, multifrequency (DTMF) signal
as each key is pressed.
You will hear dial tone after entering the “#“ if the test
passes.
the test for each touch-tone receiver.
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