AT&T System 25 - Manual (Page 257)

MAINTENANCE
Emergency Transfer Unit Trouble
If the Emergency Transfer Unit (ETU) will not enter the power failure mode, do
the following steps:
1.
2.
3.
Unplug the cable bringing the control signal from port 7 or 8 on the
CPU/Memory CP to the ETU. This cable terminates in a modular jack
that is inserted in a modular plug labeled CPU on the left-hand side of
the ETU.
If the ETU goes into the power failure mode, the CPU/Memory CP is
probably faulty or a wiring problem exists. Plug the cable back in, then
reset the CPU/Memory CP by removing and restoring power to the
system. If the ETU still does not go into the power failure mode, the
CPU/Memory CP must be replaced.
If the ETU does not go into the power failure mode after the control
cable was unplugged in Step 1, the ETU is faulty and must be replaced.
If the ETU remains in the power failure mode continuously (preventing normal
operation of the system), follow these steps:
1.
2.
3.
4.
At the ETU, unplug the cable bringing the control signal from the
CPU/Memory CP.
Using a modular jack breakout box and voltmeter, check to see that 48
volts are present between pins 1 and 2 and pins 3 and 6 of the control
cable from the CPU/Memory CP.
If the above voltages are present, the ETU is faulty and should be
r e p l a c e d .
If the above voltages are not present, either the CPU/Memory CP or the
cable is faulty and should be replaced.
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