TROUBLESHOOTING GUIDE FOR A-51 INVERTERS INSTALLATION 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) I. D-C input fuse blows. A. Check power stage. B. Check surge and DV/DT protection. C. Check oscillator printed circuit card. D. Check over and under voltage protection printed circuit card. E. Check Resonating Capacitors C3. II Fuses good - no output volts. A. Contactor does not pull in. B. Contactor pulls in but output voltage is zero or low. PROCEDURE 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    SCR’s    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  SCR’s  as  follows:    Disconnect  the  leads  to the cathodes of the SCR’s. Disconnect the gates at  terminals  2  and  7  of  the  surge  and  DV/DT card AC5. Check the continuity of the SCR’s 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 polarity directions. 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 the other. 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 resistance. 5.   Check  surge  protector  SP1,  SP2  mounted  near the SCR’s. Isolate SP1, SP2.  Ohmmeter reading should  be  open  for  both  polarities.  The  inverter can also be operated without the suppressors. I.   B.   Check  surge  and  DV/DT  protection  card.  If  the SCR’s 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. 8