Thermal Arc ARCMASTER 300S Service Manual page 67

300/400TS and 300/400S
b. Verify the no-load voltage (OCV) in High Fre-
quency TIG mode.
WARNING
This welding mode produces high frequency and
high voltage. Extra care shoul d be taken to prevent
electric shock.
1) When in HF TIG mode, the unit will gener-
ate high voltage. To prevent personal harm
and test equipment damage, mark and
then remove the indicated wire from the HF
UNIT1 shown in Figure 11-18. To prevent
electric shock, always wrap the removed
wire with electrical tape or other suitable
insulation.
Figure 11-18: Removal and installation
(To disable the operation of the HF unit.)
2) Press the Welding Mode selection button
to select HF TIG welding mode.
3) While depressing the Torch switch, verify
the OCV using a DC voltmeter. (The capa-
bility of the voltmeter should be more than
100VDC.) The check point with a tester is
the voltage between output terminal + and
-. In TIG mode, the OCV ceases 3 seconds
after you depress the torch switch.
4) The normal no-load voltage is approxi-
mately 65V.
5) Return the setting variable resistor (VR1)
to the original position.
fully clockwise:
fully counter-clockwise: VRD OFF
6) Return connection with HF UNIT1 to the
original position.
11
ADVANCED TROUBLESHOOTING
HF. UNIT1
from the HF UNIT1
VRD ON
11 – 17