Thermal Dynamics SIGNATURE PAK 1250XRTM, Owner'S Manual

Page: 47 / 68

35 SERVICE
4.5 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
power to the system for all other tests.
To check the main contactor remove the side panels of the
machine. The contactor should close when 24 VAC is
applied to lines 45 and 46 (when the torch switch is
pressed). At this time line power should be present at lines
105 and 107. Power should always be present at lines 1
and 4 when the primary power is turned on.
The high frequency transformer has too much voltage
(6000 volts AC) to check under power. The resistance of
the primary coil should be 5 ohms and the resistance of the
secondary coil should be about 20K ohms.
To check the high frequency capacitor (C10), it is necessary
to try to start the torch. The spark between the spark gap
points should be bright blue. If the spark appears to be
weak or nonexistent, disconnect the wire between the
spark gap and the capacitor and try to start the torch
again. If the spark is stronger with this wire disconnected,
the capacitor must be replaced.
The pilot arc resistor is located on the rear panel beside the
fan. Its resistance should measure 2.5 ohms between wire
10 and wire 38, and should measure 12 ohms between
wire 10 and wire 68.
A ‘quick check’ can be made on the main diodes without
removing them from the circuit. Using an ohmmeter with
the Rx1 or Rx10 scale, measure the resistance of each diode
in both directions. The readings should differ by at least a
factor of 10. If they do not differ (both high or both low)
the diode has failed and must be replaced. There are four
potential causes of diode failures. If a diode fails it is
important to check several things to make sure the replace-
ment diode will not fail:
1. Isolate and check each diode to determine which diode
has failed.
2. High frequency protection for the diodes is provided by
capacitors C4, C5, C6 and C7 which are installed be-
tween each side of the bridge rectifier. These capacitors
and their connections should be checked.
WARNING
A. Main Contactor Check
B. HF Transformer Check
C. HF Capacitor Check
D. Pilot Resistor Check
E. Main Diode Check
(continued)