Tweco 15XC CE Merlin PAK - Manual (Page 105)

Manual 0-2529 4 - 33 SERVICE
1. If the start LED (D57) does not light, use the negative
voltmeter probe on the logic board common (TP1) or
one of the J1 common pins, check the active ‘start’ input
(J1-21 for momentary start, J1-19 for maintained start
from CNC or remote pendant or J1-15 from hand torch)
for at or near 0 vdc (check the momentary with the
switch held closed). When not activated, the ‘start’
input should measure +12 - 15 vdc. If the ‘start’ input
does not drop to 0 vdc when activated, the problem is
wiring or a defective switch.
2. Check the ‘stop’ input at J10-17 for +12 - 15 vdc. Check
that the ‘stop’ input does not stay at 0 vdc. If start and
stop inputs are okay and start indicator is not lit even
momentarily replace the logic PC board.
3. If no output voltage is produced within 75 ms, the logic
removes the start signal. This makes troubleshooting
difficult. Jumping TP1 to TP4 on the logic board dis-
ables this for troubleshooting. A red LED indicator
(D38) on the logic board labeled ‘W ’ indicates that the
K2 relay (which controls the 120 VAC to J2-12) has
received the signal to turn on. If the start indicator
comes on and W does not, replace the logic board. If W
comes on, check for 120 VAC between wire #110 (120
VAC return) and J2-12. If 120 VAC is not present,
replace the logic board.
4. If 120 VAC is present at J2-12, check J6-1 and J6-3 on the
voltage selection board. If voltage is present at only one
of the two points, replace the contactor. If voltage is
present at neither or both points, replace the voltage
selection board.
To produce DC output, the main switch (Q1) must be
turned on and off rapidly. Power supply output is con-
trolled by the on-time. At the same time the main contac-
tor (W1 or W2) closes, the logic board grounds pin 9 of the
34-pin ribbon cable (J3-9 on the logic board, J10-9 on the
switching control board). This enables the pulse width
modulator (PWM) on the switching control board.
If no DC voltage is detected within 75 ms at J1-24 on the
logic board, the enable signal on J10-9 is removed and the
main contactor opens. Connecting TP4 to TP1 (ground) on
the logic board disables this function for troubleshooting if
no DC output is found.
J. Main Contactor Circuit
(continued)
K. Switching Control Check
(Q1)