18 Systematics , Inc. 1025 Saunders Lane West Chester, PA. 19380
TESTING AND REPLACING
DIODES
Silicon diodes have proven to be
highly reliable. However, weld
spatter build-up in the torch can
short out and cause diode overload
and consequent failure. The fol-
lowing information is provided as
a guide should a failure be sus-
pected.
Silicon diodes exhibit two main
fault conditions:
1. "Open Circuit" - causes a re-
duction in welder output.
2. "Short Circuit" - causes the
circuit breaker to trip.
If a fault is suspected, the
diode may be tested as follows:
1. Remove the top connection of
each diode to be tested.
2. Using a Volt-Ohm Meter set on
RX1K, check for continuity
through the diode in both di-
rections. If there is no
continuity in either direc-
tion, the diode is in "open
circuit" condition and must be
replaced. If there is continu-
ity in both directions, the
diode is in "short circuit"
condition and must be replaced.
If there is continuity in one
direction only, the diode is
functioning properly.
CAUTION
+-
+-
12 VOLT
LIGHT BULB
DIODE 12 VOLT
BATTERY
12 VOLT
LIGHT BULB
DIODE 12 VOLT
BATTERY
3. If all the diodes check out
satisfactorily with the Volt-
Ohm Meter, a load check must be
made. This is easily accom-
plished using a twelve volt
battery and a twelve volt light
bulb connected as shown. Again
test for electrical current
flow in both directions. The
bulb should light in one (1)
direction only - not both.
NEVER use a "megger" or a
high voltage device to
test a diode.
4. When replacing diodes, it is
very important that a heat
conductive compound (Radio Shack
#276-1372) be used where the
diode makes contact with the
aluminum heat sink. Do not
grease the threads on the di-
ode.
FIGURE 16. DIODE LOAD CHECK
CONNECTION DIAGRAM
- TEST FOR FLOW IN BOTH DIRECTIONS
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