Now test the other halve of the bridge. Connect the yellow negative clip to the positive bridge output bus bar at the left. Connect the red positive c...
I design and test high power equipment that uses large SCRs (silicon controlled rectifiers). Sometimes one will go out. I use 6 in a three phase bridge configuration and if one goes out, its difficult to find the bad one without taking them all out. You can make a "in circuit" tester out of a flashlight.
An SCR is a Silicon Controlled Rectifier. They are used in power supplies, welders, inverters and other equipment for controlling power. The one below can carry 350 amps of DC current with a rating of 2400 volts. Think of them as a diode that can be turned on with a small current to the gate. Once turned on, they stay turned on till the current flow is interrupted or below the minimum current. Large SCRs like this one requires 150 milliamps at 3 volts to turn on. The SCR behaves like a solid state latching relay. The large base at the left is the Anode and attaches to a heat sink. The "pigtail" end at the right is the Cathode and the white wire is the Gate. The additional skinny red wire is connected to the cathode and is used with the gate when connected to a triggering circuit.
Step 2: The Circuit
To test the SCR, you need to connect a power source to the device. The anode connects to positive and the Cathode connects to negative. The flashlight's light bulb is in series and limits the current through the SCR to about 400 milliamps. A flashlight can be modified to make the tester. You can also use the modified flashlight as a continuity tester, test diode polarities and smaller SCRs.
Step 3: Drill a hole
You will need to bring out three wires at the end of the flashlight. Start by drilling a hole just big enough for your wires. I used a Yellow, Red and White 18 gauge wire.