Chapter 5. Diagnostics
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6. If the red FAIL LED is illuminated on the power supply front panel, the power supply
over/under voltage detectors or fuse failure alarm circuitry has activated. Check for an alarm
indication on the fuse(s) by removing, inspecting, and replacing each fuse. If there is no
alarm indication, proceed to step 8 below.
7. Measure the DC voltage at the test points indicated on the power supply front panel. These
are approximately equal to the actual voltages on the backplane. Use a high-impedance
(greater than 1 megohm) DC voltmeter for all measurements. Acceptable readings are
within 10% of the marked voltages.
8. If a replacement power supply also shows a red LED failure and the DC voltage check
indicates that one output is low, a possible cause is a shorted card elsewhere in the shelf.
To check for this, systematically remove non-power supply cards from the shelf while
observing the power supply failure light. Removal of the shorted card will allow the voltages
to restore themselves and will extinguish the power supply FAIL LED.
9. Check the D/I Mux III system software programming using the Display line Card
configuration (DC), Display system Parameters (DP), and related commands.
Common Equipment and Line Card Testing
The primary method of isolating trouble in the D/I Mux III line cards is by replacing the suspected module
with a known good one.
Note: When changing plug-in units, allow at least two minutes for the alarms to clear before continuing. If replacing
common equipment, power down the shelf first, then swap cards as appropriate. Follow this procedure for
replacement of the LIUs, CCU/MCU, strobes and power supplies.
1. Replace the suspected module.
2. Test the replacement module to verify normal operation.
3. If the replacement does not clear the trouble, remove it and verify all option settings, then re-install
the original module.
4. Repeat steps 1 through 3 on the next suspected module.
Defective Units
DO NOT ATTEMPT TO REPAIR PLUG-IN UNITS. Return defective units per instructions in the D/I Mux
III warranty.
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