System Troubleshooting
6-11
Figure 6-10 FBUS+ PIU Troubleshooting – MOD OK LED Off
Front
BXB-0655-95
MOD OK
OC
OT
OV
48V
RESET
V-OUT
DISABLE
ENABLE
MOD OK
OC
OT
OV
48V
Both
MOD OK
LEDs Off
Yes
B
A
Check the CCL-to-PIU cabling.
Check that the DISABLE/ENABLE
switch is in the ENABLE position
(down).
No
Only one
MOD OK LED
Off
Replace that regulator.
Regulator A and B in the FBUS+ PIU are dependent on each other. For
the MOD OK LEDs to be on, the following sequence of power applies: 3
volts from A, followed by 5 volts from B, followed by 2 volts from A.
Therefore, if any one of the voltages fails, both regulators will turn the
MOD OK LED off.
