
F-34
F-34
PRECISION TIG 375
TROUBLESHOOTING & REPAIR
STATIC SCR TEST
(continued)
TEST PROCEDURE
1. Remove main supply power to the Precision
TIG 375 and remove the case top and left
side.
2. Locate and remove plug J4 from the control
board. See Figure F.6.
3. Using an analog ohmmeter, test the resis-
tance from anode to cathode of SCR1.
Reverse the meter leads and check from
cathode to anode of SCR1. See Figure F.7. If
a low resistance is indicated in either direc-
tion, SCR1 is faulty. Replace the SCR Bridge
Assembly. See
4. Repeat Step #3 testing SCR2, SCR3 and
SCR4.
5. To further check the SCR’s functions, use an
SCR tester and proceed to the
NOTE:
Also check diode D1.
6. Replace plug J4 on the control board.
7. Replace the case top and left side.
Plug
J4
G3909
Figure F.6 - Plug J4 Location
Figure F.7 - SCR BRIDGE LOCATION
Note
: The negative half of the
SCR Bridge is located on the
top left side of the machine.
The “Finned” heat sinks are
the cathode test points for
SCR 3 and 4. The “Non-
Finned” heat sink is the
anode test point for SCR 3
and 4.
The Positive half of the
SCR Bridge is located on the
top right side of the machine.
The “Finned” heat sinks are
the anode test points for SCR
1 and 2. The “Non-Finned”
heat sink is the cathode test
point for SCR 1 and 2. See
Wiring Diagram.