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25 August 2008

Checking transistor controllers


After battling with Gordon's' economy transistor controller, I had to come to the conclusion that the transistor may be fritzed. Before getting round to testing the transistor, I spotted this simple way to test on a web site:
"With the meter set to measure ohms, clip one meter lead to the base connection of the transistor. Touch the other lead first onto the collector lead and then onto the emitter lead. The readings should both be the same, either both high resistance or both low resistance.
Now reverse the leads and repeat the procedure. The results should be the opposite of those obtained before. If they were both high before they should now be both low. If they were both low before they should now both be high.
Now measure the resistance between emitter and collector. It should read high resistance in both directions.
Note that for this to work the internal battery of the meter must supply a voltage high enough to overcome the forward resistances of the transistors. Many meters have a position marked with a diode symbol which must be selected when checking transistors or diodes."
(not sure where I lifted the reference pic but suspect in was from Chris Frost's excellent web site on transistor controllers).

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