Tweco 15XC Merlin - Manual (Page 101)

Manual 0-2251 5-29 CUSTOMER/OPERATOR SERVICE
5.12 SERVICE AND TEST PROCEDURES (continued)
120 VAC is supplied to the motor control contactors (MC1
and MC2) from the voltage selection PC board, which
selects the proper tap on the main transformer (T1). The
return path (see Figure 5-J) travels from wire #110 through
the remote connector (J15) on the rear panel to the E-Stop
switch (or if no remote is used, through K1 on the switch-
ing control board) to wire #8, through the ON/OFF switch
(SW1A) to wire #9, through fuse F2 to wire #10 and T1.
Only one of the MC contactors should have voltage ap-
plied. If the red LED indicator (D18) on the voltage selec-
tion board is lit, MC2 should be energized. If D18 is not lit,
MC1 should be energized.
1. Check the voltage across the coil on the contactor for
approximately 120 VAC. If voltage is present, replace
the contactor. If it is not, perform the 120 VAC test (see
Section 5.12-Test A) to check for a proper voltage sup-
ply from the voltage selection board. If okay, continue
to step 2 to isolate the problem in the return path.
2. With one meter lead on the supply side of the contactor
coil (wire #3 for MC1 or wire #4 for MC2) measure to
wires #8, 9, and 10 to determine where the return circuit
is broken. On the return path, F2, SW1-A, and E-Stop
can be measured for continuity. K1 on the switching
control board will normally be open when power is off.
3. When the remote control cable is installed, a jumper
between J15-26 and J15-27 pulls J7-20 on the switching
control board to 0 V (board connector J7-19). When the
jumper is not in place (remote cable is not plugged in)
J7-20 measures +15 vdc and K1 should energize, by-
passing the E-stop function. If not, replace the switch-
ing control board.
There are fourteen diodes in the main heatsink area,
including six large 150 amp input rectifier diodes (D1-6)
and eight small 70 amp diodes (snubbing diodes D7-10
and freewheeling diodes D11-14). To check the diodes
without removing them from the circuit, use an ohmmeter
set to the Rx1 or Rx10 scale to measure the resistance of
each diode in both directions. The readings should differ
by at least a factor of ten. If they do not differ (both high
and low), replace the diode. Check all diodes before
turning on power to the system.
C. Motor Control
Contactor Check
(MC1 or MC2)
D. Diode Check