6 pins and 4 pins Optoisolator
Testing the 6 pins optoisolator IC was not a problem for most of the beginners but for testing a 4 pins optoisolator you may have some problem. First after you have search from the internal schematic of the IC you found that the 4 pins opto does not have the base pins and you do not know how to measure it. Its actually simple, by just measuring the colletor and the emitter pins using analog meter set to x 10 K Ohm and it should have one high ohm reading.
In fact for those who already got my ebook “Testing Electronic Components” just by referring to the testing transistor topic i believe it would be easy for you to test on the 4 pins optoisolator ic. Remember the other two pins is LED and it should have one reading under X1 and X10 K ohm range.
Now let me share with you that not all optoisolator will have the same reading. The reason for it was that the opto that you have checked does not have transistor inside, infact it was a diac and other components. In certain model of laser printers power supply they actually used the optoisolator that have a diac inside and a good one should not show any reading even under X10 K ohm range.
So in order to avoid this kind of problem in the future please find out the part number and check what is inside the internal part of the optoisolator IC first before you do the testing.