Don't Miss

Missing Part Number?

By on July 2, 2009


I got an email that asked about what would i do if i come across a Transistor that do not have part number printed on the body.

My answer to him was use the highest spec of transistor and test it out (assuming you can’t get the exact model of schematic diagram). Of course we can’t simply just get any high rating transistor and put it in, in fact we need to know what type and in which circuit the transistor was found.¬† Assuming if you found a transistor in the power section, most likely the transistor would be the power N-channnel FET. Now how did we know it is N-channel FET and not P-channel or even bipolar transistor?

Simple, just get other model of schematic  diagram and see what type of transistor it is using. From there you will roughly know the type of transistor and the specification too if you look for the transistor data. You then get an equivalent part number and retest it. One more advice, before you put in the new replacement part number be sure that you have check all the corresponding components otherwise the new transistor will blow again the moment you power up the set.

Another way is to get help from repair friend and forum and hope that they could provide an answer for you.



  1. Waleed

    July 3, 2009 at 3:30 am

    test the part and the reading should tell you if that is a mos N fet or a transitor. for mos n fet, I always use Buz 90 and it works every time. also the reading on the pc board should tell you what it is and where is the source, drain and gate.
    I never came across a part that does not have numbers on it. so far so good.

  2. admin

    July 4, 2009 at 1:12 pm

    HI Waleed,

    Yes that was true but some board do not have the board location label and some company (i came across one company that sell UPS)purposely remove/erase the part number not only to transistor but to ICs too. This will make the repair technician have a hard time in fixing the UPS.



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Your email address will not be published.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.