Don't Miss

6 pins and 4 pins Optoisolator

By on January 19, 2009


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.



  1. Akhtar

    May 8, 2009 at 12:47 pm

    Free help to any one is greatness and you are doing so. Very good
    Please continue, God bless you

  2. admin

    May 8, 2009 at 11:28 pm

    Hi Akhtar,



  3. tech_dan

    July 6, 2010 at 9:38 pm

    thank you for concern sir

  4. Songre

    December 18, 2010 at 1:59 pm

    Hi Jestine, happy holidays to you and your family at this time all the best and have a great year, next year. I am subscribed to your news letter and I am receiving it. You are the best my Brother...thanks again for everything.....Cheers!

  5. admin

    December 19, 2010 at 12:07 am

    HI Songre,

    You are welcome!


  6. Peter

    April 9, 2011 at 2:06 am

    This is great! i was so poor on optos, it has worked for me. good time tech.

  7. ahmed

    July 22, 2012 at 2:08 pm

    my printer cannon 2900 usb card is formated how to working plz help me sir

    • Jestine Yong

      July 23, 2012 at 10:00 pm

      Hi Ahmed,

      May I know what do you mean by your USB card is formated?


  8. bora

    August 15, 2012 at 2:23 am

    dear! Mr. jestine
    i just got ur webside
    this web is good for all technician for solve problem
    i hope that
    u will continous to do it more
    have a nice time
    good luck
    god blest to u

  9. bora

    August 15, 2012 at 2:26 am

    i have problem with my photocoupler  and mosfet , varistor, phototransistor.
    i don't know how to measurement of photocoupler or optocoupler
    if u got my comment please soon reply to me cos i need to repairing my equipment

    • Jestine Yong

      August 15, 2012 at 11:36 pm

      Hi Bora,

      Try this link:



Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.