TROUBLESHOOTING GUIDE FOR A-51 INVERTERS
If the unit is newly installed and does not function,
recheck installation and operating instructions.
Check the nameplate data input voltage, input and output
connections, fuses, etc. Check to see that terminals 1
and 2 on the terminal board are jumpered.
Check reverse polarity fuse (F3). If fuse blows, check
input cables for reverse polarity.
OPERATING FAILURE (See Procedure)
D-C input fuse blows.
Check power stage.
Check surge and DV/DT protection.
Check oscillator printed circuit card.
Check over and under voltage protection printed
Check Resonating Capacitors C3.
Fuses good - no output volts.
Contactor does not pull in.
Contactor pulls in but output voltage is zero or
I. A. Power Stage
1. Remove small 4 amp fuse F2. Removing this
fuse de-energizes the pilot start relay which
controls the main contactor. The oscillator is also
de-energized so that the gates to the silicon
controlled rectifiers (SCR) are not energized.
2. Manually close the contacts DK-1 of relay DK.
This connects the battery to the mainpower
stage. If the SCRs are shorted, the relay
contacts will draw a big arc. If the contacts
remain closed, the main d-c fuse Fl will blow.
On small low voltage units, the contactor may be
totally enclosed. In this case, the relay contacts
can be closed by energizing the relay. To
energize the relay, turn on the on-off switch and
short out terminals 3 and 5 on the over and
under voltage card AC3.
If the main fuse blows, one of the fe JI back diodes
SD1 and SD2 or the S( may be shorted. Check
the SCRs as follows: Disconnect the leads to
the cathodes of the SCRs. Disconnect the gates
at terminals 2 and 7 of the surge and DV/DT
card AC5. Check the continuity of the SCRs with
an ohmmeter. Clip the ohmmeter leads to the
anode (heatsink) and cathode, check continuity,
reverse leads or polarity and check continuity
again. The meter should read open circuit in both
3. Check feed back diodes SD1 and SD2.
Disconnect the wire to the cathode end (pigtail) of
the diode so that one end of the diode is free.
Check continuity with ohmmeter from pigtail end
of diode to the heatsink. Ohmmeter should read
continuity in one direction and high resistance in
4. The commutating capacitors can be checked
for a shorted or open condition with an
ohmmeter. Disconnect the wires from the
capacitor terminals, and momentary short the
terminals to ins that the capacitor is discharged.
Connect the ohmmeter leads to the capacitor
terminals. The meter should indicate a low initial
resistance and gradually increase to a high
5. Check surge protector SP1, SP2 mounted near
the SCRs. Isolate SP1, SP2. Ohmmeter reading
should be open for both polarities. The inverter
can also be operated without the suppressors.
B. Check surge and DV/DT protection card. If the
SCRs in test I.A. are not shorted, the DV/DT
circuit may be shorted.
1. Reconnect all wires disconnected in test L. A.
2. Remove wires from terminals 4 and 5 of the
surge and DV/DT card AC5. This completely
disconnects the snubber circuits.
3. Try to start the unit by turning the DC switch to
the "ON" position. The verter may be operated
with these minals disconnected.