TOSHIBA - 70
TX Series 48 - 1250A
7.2 SCR Testing Procedure
Failure to remove both line and control power
before starting this procedure may cause
personal injury or death.
Remove both line power and control power from the unit and lock out.
Disconnect any two motor load leads and any two line leads. Disconnect
the SCR connections to main control board J5, J6 and J7. Refer the
Chapter 6 for the main control board layout. Note the type of color coding
of the wires connected to J5, J6 and J7. Toshiba uses two possible
configurations. Both configurations have 4 wires going to each plug. The
first configuration consists of 4 wires color coded black, yellow, grey and
white. The second configuration consists of 4 wires color coded red, white,
red, white.
The testing procedure for SCRs is comprised of two separate tests. The
first one tests the anode to cathode integrity of the SCR by performing the
following ohm checks:
The second tests the gate to cathode integrity of the SCR. The chart below
indicates good versus bad readings.
Note: If any of the above readings are out of specifications, replace
the faulty SCR.
Note: The best way to test an SCR is with an SCR Tester and look for
leakage current less than the manufacturer specified values.
