4.12 GENERAL TROUBLESHOOTING PROCEDURES - CONTINUED.
(2) To check for voltage to the logic circuits, use a multimeter set to measure ac voltage and carefully touch
probes to terminals 1 and 3 on TP6. Line voltage should be indicated (nominally 208 vac). If no power is
(3) To check for voltage to the solid state relays (SSR's) output control switches, use a multimeter set to
measure ac voltage and carefully touch probes to terminal 3 on TP6 and terminal 8 on TP3. Line voltage
should be indicated (nominally 208 vac). Note that this only confirms that power is being supplied to the
output control fuse (J3/Fl). If no power is indicated, check the interconnecting wiring per paragraph 4.16.
(4) To check the output control fuse (J3/F1), disconnect power from the FDECU and carefully remove the fuse.
Using a multimeter set to measure continuity, check continuity between fuse terminals. Continuity should
be indicated. If no continuity is indicated, discard the fuse and replace it with the spare fuse located at the
top of the pc board. Replace the spare fuse as soon as possible.
(5) To check the SSR's, connect power to the FDECU then carefully place the dual inline parallel (DIP) switch
(S3) into the maintenance mode by pushing switch 8 to the ON position (down). Each of the remaining DIP
switches correspond with one of the SSR's. Place each DIP switch 1 through 7 to the ON position (down)
and observe the LED adjacent to the associated SSR. The LED should come on and the component
controlled by that SSR should also operate confirming voltage at the SSR output. If the component does
not come on or cannot be detected, check voltage across the associated SSR as follows: Using a
multimeter set to measure ac voltage, carefully touch probes to terminal 8 on TP3 and the associated
terminal 1 through 7 on TP3. Minimal voltage should be indicated (less than 5 vac) if the fuse J3/F1 is good
and the SSR is closed. Line voltage (nominally 208 vac) would indicate a blown fuse or open SSR. If this
occurs, test the fuse J3/F1 and replace if necessary. If line voltage is indicated after replacing the fuse, the
SSR is defective and the pc board must be replaced. If a feedback signal is being received from a
component contactor (component operating) without a control signal going to that contactor, the pc board
will enter a major failure mode (completely shut down) and the binary indicators will display the terminal
number on TP1 associated with the failure. To determine whether the associated SSR or component
contactor has fused closed, check the output voltage of that SSR to see if it is sending a signal. If it is,
carefully pull fuse J3/F1, using insulated tool, to open the circuit. If the contactor opens (component shuts
off), this will confirm that the SSR has fused closed and the pc board must be replaced. If the component
continues to operate, then the contactor has fused closed and must be replaced.
(6) If pc board failure is suspected, notify direct support maintenance to v rify and replace as necessary.
Lethal voltage levels are used in operating the FDECU. Be sure power has been
disconnected prior to servicing the unit. Injury or death can occur if personnel
contact any electrical terminal while the unit is connected to power source.
b. Contactors K1 through K5. Be sure power has been disconnected prior to testing the contactor.
Tag and disconnect leads from contactor coil terminals A1 and A2. Using a multimeter set to measure
continuity, check continuity between coil terminals. Continuity should be indicated. Connect wire leads per
tags. Remove tags.