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Yes, these devices work with much higher voltages as your meter and at that point C and G are blocking - they go up to 200 to 1000 VAC between A and C with only a few volts needed on G to turn on
A SCR fails only in two ways:
1. It doesn’t turn ON at all
2. It turns on On all the time
It basically looses its ability to act like a switch or relay
Ok, C and G are like a Diode - however it doesn’t matter - the only two questions which matter for an SCR is that A and C are conducting when G is connected to A and it stops conducting when G is removed from A - this test has to be performed in Ohm setting on DMM not diode test
Only between C and A if G is connected with an extra wire to A while A is on your DMM Plus Lead and C on the Black Lead - you need three hands for this test - G acts like an on off switch when connecting to A
If conducting between C and A in either direction with G not being connected to A = failed with short
If not conducting between C and A when G is connected to A = failed open
Procedure to Test the SCR with the help of Multimeter:
To test the SCR, keep the Multimeter into Ohmmeter mode.
Connect the positive output lead of the multimeter to the anode and the negative lead to the cathode.
The multimeter should indicate no continuity.
Touch the gate of the SCR to the...
That’s an scr with one leg being the gate and the other two anode and cathode -
http://www.completepowerelectronics.com/how-to-test-scr-with-multimeter/
Ok, desolder R1 and R3 and check resistance, if they check Ok, take a close look at T1 - check primary coils for dc resistance - if they check ok check Q1 and Q2
Ok, check the six Diodes CR1 to CR6 for short - you may have to desolder each lead to test each Diode individually - if your meter has Diode test, then note voltage drop in conducting direction and check that the diode blocks in block direction
That’s good, pass now onto test 3 - you may want to connect your rheostat to 120VAC as in test 1 with phase and neutral - set to 12VAC apply that to each coil system as in wiring diagram
For test 2 I would leave only the phase 240VAC connected to rheostat and connect wiper to T2 H1 and The other phase of 240VAC connected to T2 H2
Adjust rheostat to 208VAC across T2 H1 and H2
Take the white wire off the rheostat, connect it to one side of R2 if this neutral.
Leave black wire on rheostat if this is your phase 120VAC, connect wiper to other side of R2 - apply power and adjust to 95VAC across R2 - then check voltage on VR board in DC range
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