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SQUARE WAVE TIG 255
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F-27
TROUBLESHOOTING & REPAIR
STATIC SCR TEST
(continued)
PROTECTION/SNUBBER
L9255
J10
J11
J12 J13
J14
J15
REMOVE PLUGS J10 & J13
TEST PROCEDURE
1. Remove main supply power to machine
2. Remove plug J10 and J13 from the pro-
tection/snubber board. Refer to Figure
F.11.
3. Remove red insulating paint from heat
sink test points. See Figure F.12. DO
NOT DISASSEMBLE THE HEAT
SINKS.
4. Using an analog ohmmeter test the
resistance from anode to cathode of
FIGURE F.11 - PROTECTION BOARD PLUG LOCATIONS
SCR1
ANODE
CATHODE
(1 & 2)
SCR2
ANODE
SCR3
CATHODE
SCR4
CATHODE
ANODE
(3 & 4)
PLUG
P10
FIGURE F.12 - SCR TEST POINTS.
SCR1. Reverse the meter leads and
check from cathode to anode of SCR1.
A. If a low resistance is indicated in
either direction SCR1 is faulty.
Replace SCR assembly.
5. Repeat Step 4 testing SCR2, SCR3 and
SCR4.
To further check the SCR’s functions
use an SCR tester and proceed to
active SCR test.