Thermadyne Thermal Dynamics PAK MASTER 50XL, Service Manual

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Manual 0-2587 25 SERVICE TROUBLESHOOTING
The indicators on the Gate Drive PC Board as follows:
Gate Driver PC Board
A-01200
D34
RESET
D3
POWER ENABLE
Indicator Meaning
D3
Power Enable - When ON PWM Enable
received from the Logic PC Board.
D31
Reset - Indicator will blink if
primary over-current is detected
when torch switch is pressed.
1. No DC Output
An open circuit voltage of approximately 280 to 325
VDC (depending on input power selected) is pro-
duced when switching transistors in the FET/
Heatsink Assemblies are turned ON by a PWM En-
able signal from the Logic PC Board. A circuit on the
Logic PC Board monitors the output voltage. When
the output voltage drops below 60 VDC, indicating a
problem exists, the Logic PC Board sends a signal
which turns OFF the PWM Enable signal to the Gate
Drive PC Board. Because this happens in less than 50
milliseconds, it is not easy to take voltage readings to
find the source of the problem.
When the unit is at “idle” the AC OK indicator, D34,
should be ON. The Torch Switch Enable indicator,
D5, turns ON when the torch switch is pressed. At
this point the gas begins to flow. When the preflow
time is over the PWM Enable signal is given and the
DC indicator at the front panel turns ON. When the
pilot arc is established the Pilot On indicator, D33,
turns ON.
If the PWM Enable indicator, D3, does not come ON
then replace the Logic PCB.
If the PWM Enable indicator, D3, turns ON then OFF
immediately, the following test should be performed:
a. Disconnect J11 from the CD PC Board to dis-
able the CD signal.
A-01202
J11
CD PC Board