Tweco 15XC Merlin - Manual (Page 99)

Manual 0-2251 5-27 CUSTOMER/OPERATOR SERVICE
5.12 SERVICE AND TEST PROCEDURES
The following tests are suggested for specific problems
listed in the troubleshooting guide. The letter designations
correspond to those listed in the “Remedy” column of the
troubleshooting section.
Several of these tests involve voltage measurements that
must be made with power on. Use extreme care when
making these tests. Tests requiring voltage measurements
are marked with the warning symbol. Disconnect primary
WARNING
A. Voltage Selection
PC Board Check
When wall power is first turned on, the voltage selection
PC board (see Figure 5-G) senses the low voltage AC
present at J6-20, J6-22, and J6-24 (center tap). The voltage
selection board determines whether the voltage is in the
lower or higher part of the selected input voltage range. If
the input voltage is within the upper part of the range, the
board energizes K1, K4, and K5 relays (labeled ‘HV’ on the
system schematic). If the input voltage is within the lower
part of the range the board energizes the K2 and K3 relays
(labeled ‘LV’ on the schematic). If HV is selected, the red
LED indicator (D18) on the voltage selection board will be
lit. The relays do not energize until SW1-B (one pole of the
ON/OFF switch) is closed because the DC voltage to the
coils passes through it.
1. Check the AC input from J6-24 to both J6-20 and J6-22
for 12 - 18 VAC.
2. Check the AC voltage from J6-24 to both J6-17 and J6-18
for 16 - 22 VAC.
3. If input voltages are correct, check output from J6-19 to
J6-21 for 14 - 18 VAC.
4. If output is not present between J6-19 and J6-21, check
between J6-24 (-) and both J6-16 and J6-23 (+) for 12 - 16
vdc. If voltage is present at both points or neither,
replace the voltage selection board. If voltage is found
at J6-23 but not at J6-16, check SW1-B and all wiring and
connections.
28 VAC Test