Troubleshooting & repair, Switch board test (continued), Warning – Lincoln Electric INVERTEC SVM129-B User Manual
Page 72
TROUBLESHOOTING & REPAIR
F-34
F-34
INVERTEC® STT® & STT® II
SWITCH BOARD TEST (continued)
FIGURE F.11 - SWITCH BOARD RESISTANCE TEST
TEST PROCEDURE
NOTE: There are two switch boards. One is
located on each side of the machine.
NOTE: The switch boards are designed to
receive gate (turn-on) signals from the
driver board (pulse transformer secon-
daries). The internal board circuitry
processes the signals and outputs them
to the FETs. The switch board circuitry
contains snubber circuitry to protect the
FETs. This protection is supplemented
by off-board resistors. The switch board
design accommodates the connection
point(s) for the capacitor(s), main trans-
former primary windings, input rectifier,
and reconnect switches.
1. Turn off INVERTEC® STT® & STT® II and
disconnect main AC input power to the
machine.
2. Using the 5/16" nut driver, remove the case
wraparound cover.
3. Perform the Input Filter Capacitor
See
the
Maintenance section.
ELECTRIC SHOCK can
kill.
• Before continuing with the
test procedure, perform
the capacitor discharge
procedure to avoid electric
shock.
4. Disconnect all wiring harness leads (401/403,
1/8, 9, 12, 4/5, 402/404) from the switch
board.
5. Fold the leads up so they do not interfere with
the exposed terminals. See Figure F.11.
6. Using an analog ohmmeter, perform the resis-
tance tests detailed in Table F.5 and shown in
Figure F.11. If any test fails, replace both
switch boards. See the Switch Board
Removal and Replacement procedure.
7. If the switch boards appear to be burned or
overheated, or if the machine was supplied by
a 380 VAC or higher voltage supply when the
failure occurred, replace the capacitors and
the switch boards.
WARNING