Service Manual
Test Procedures
7 - 25
3x3 UPS
Issue 2 - November 2001
To functionally test a single SCR and diode pack as shown in Figure 7Ć12 a DC power source and test
lamp is required, typically a 9V PP3 battery and 12V bulb.
1.
Connect the bulb and battery to the SCR as shown, connect the +ve to the anode (1) and
ćve to the cathode (2) terminal.
2.
Using a second power source or link from the battery connect the +ve lead to the SCR gate
terminal 4 and the ćve lead gate terminal 5.
3.
Switch on the SCR by briefly making the gate circuit, use a switch if available.
The SCR will fire and the bulb will light and remain on. The bulb provides a current source
for the SCR and it will continue to fire.
4.
Remove the +ve connection from terminal 1.
The bulb will extinguish an the SCR will switch off.
5.
Using a DVM set to the diode range check the individual diode between SCR terminal 1 and
3 for the forward and revers conditions.
