4-2-1. Troubleshooting the Power Supply Unit. Fault isolation of the Power Supply Unit to a defective
component(s) can be accomplished with the use of a Model 8840A/AF-05 Digital Multimeter (or equivalent) and
120 VAC, 60 Hz and +28 VDC power sources.
Based on the reported fault, follow the schematic diagram, checking for shorts, open circuits, or continuity. Use
the circuit breakers and switches for isolating sections of the unit, and if necessary, disconnecting P1 from the
8VDC power supply to isolate this section. With the multimeter set for ohms, check for continuity, opens, or
shorts, as appropriate.
The following table lists symptoms and probable cause(s) of the most likely faults.
Table 4-1. Power Supply Unit Troubleshooting
AC INPUT POWER LED does not illuminate, AC power output
Check R1, CR1,CR2.
present at AC connector J4 and RDF connector J6.
DC INPUT POWER LED does not illuminate, DC power output
Check R2, CR3.
present at DC connector J5 and DCT connector J3.
RDF LED does not illuminate, power output present at RDF
Check R3, CR4, CR10.
PROCESSOR LED does not illuminate, power output present
Check R4, CR5.
DCT connector J3.
AC or DC PWR circuit breaker trips when power applied.
Replace circuit breaker.
No power output at RDF connector J6, power output present at
Check S1, J6.
AC connector J4.
No power output at AC connector J4, power output present at
Check S2, J4.
RDF connector J6.
No power output at DCT connector J3 with DC primary power
Check CR6, S2.
applied, power output present with AC primary power applied.
Check CR7, CR8, T1, S2.
No power output at DCT connector J3 with AC primary power
applied, power output present with DC primary power applied.
Check C1, C2 for short. Check
No power output at DCT connector J3 with either AC or DC
8VDC Power Supply.
primary power applied.
AC output at AC connector J4 and RDF connedor J6 low.
DC output at DC connector J5 low.