Spark Gap Adjustment; Testing Diodes; Important - ESAB ESP-150 Manual De Instrucciones

SECTION 5
Voltages in plasma cutting equipment
are high enough to cause serious injury
or possibly death. Be particularly careful
around equipment when the covers are
removed.
Be sure that all primary power to the ma-
chine has been externally disconnected.
Open wall disconnect switch or circuit
breaker before attempting inspection or
work inside of the power supply.
Voltages in plasma cutting equipment
are high enough to cause serious injury
or possibly death. Be particularly careful
around equipment when the covers are
removed.
C. SPARK GAP ADJUSTMENT
The spark gap, which is part of the high frequency generator, is factory set at 0.040-in.
(+/- 0.002). After extended operation or if erratic operation is noted, it may be neces-
sary to readjust or replace the electrodes. Use a feeler gauge when readjusting the
gap. Cleaning or dressing of the spark gap electrodes is not recommended. When
replacement is necessary, both electrodes should be replaced.
D. TESTING AND REPLACING BRIDGE ASSEMBLY COMPONENTS
The silicon diodes and SCR's used in the power supply are devices which allow current
to flow in only one direction. They block current in the other direction. The diodes and
SCR's are designed to provide long troublefree operation; however, should a failure
occur, they may require replacement.

1. Testing Diodes

a. Locate the main rectifier assembly containing the silicon diodes and
SCR's.
b. Electrically isolate main bridge rectifier assembly by disconnecting
the main transformer secondary fuse links F1 and F2.
c. With ohmmeter on RX1 scale, place negative lead on the diode heat
sink and touch positive lead to each pigtail terminal. Meter should
read a low resistance of approximately 3 to 15 ohms on each diode.
d. Reverse leads and check each diode. All readings should show high
resistance of 2 K (2000) ohms or higher. With most ohmmeters on the
RX1 scale, 2K ohms is the highest possible reading available.
e. Since diode resistance is non-linear with voltage (using any scale),
diodes are good when they show low resistance in one direction and
high resistance in the opposite direction. They are bad when they
show no or very low resistance in both directions (shorted), or if they
show very high assistance in both directions (open).
2. Testing SCR's
a. Follow steps a. and b. under Testing Diodes. Disconnect the SCR pigtail.
b. With ohmmeter on RX1 scale place the negative lead on the anode
(end of SCR with screw threads) and positive lead on the cathode
(pigtail end). Meter should read a high resistance of 2 K (2000) ohms
or higher.
c. Reverse leads and check each SCR. All readings again should show
high resistance. When SCR's are bad they show low resistance in either
direction.
d. Now check the gate circuit on the SCR's by placing the negative lead
to the gate (wht wire off SCR) and the positive lead to the cathode.
Meter should read approximately 20 ohms and should vary only
slightly (5 ohms) when leads are reversed. If the meter reads zero or
infinity in either direction the gate circuit is faulty and the SCR should
be replaced.
IMPORTANT: When replacing Diodes or SCR's make sure mounting surfaces
are clean. Coat mounting surfaces with Alcoa No. 2 EJC Electri-
cal Joint Compound (no substitutes) available in 8 oz. bottles
under P/N 73585980. Use a torque wrench to tighten diodes
and SCR's. Recommended torques are 20-30 in.-lbs. for diodes;
125-150 in.-lbs. for SCR's.
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MAINTENANCE