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How to identify a primary side of a FLYBACK ?

Discussion in 'General Electronics Chat' started by ranatungawk, Oct 10, 2011.

  1. ranatungawk

    Thread Starter AAC Fanatic!

    Oct 30, 2008
    • How to identify a primary side of a FLYBACK ? (only a FBT which has removed from the board).

    • I have a SAMPO flyback of a 17’ IBM monitor. But I couldn’t find any t technical information on it from the internet. Do you know how to find a sillier one ?

    • are there any data-sheet sites for FBT on the internet ( such as for semiconductor- datasheet) ?
  2. iONic

    AAC Fanatic!

    Nov 16, 2007
  3. DerStrom8

    Well-Known Member

    Feb 20, 2011
    The best (and safest) way to do that would be to test each combination of pins with an ohmmeter. The primary coil generally has a resistance of between 1 and 10 ohms.

    Be careful with these things. they often have built-in voltage triplers, which mean high voltage caps potted inside. These can store a dangerous charge. Please take all necessary precautions before attempting to fool around with it. ;)

    Good luck!
    Der Strom
    ranatungawk likes this.
  4. Lundwall_Paul

    Active Member

    Oct 18, 2011
    Check each winding and go for the lower resistance reading that will be the primary.
  5. DerStrom8

    Well-Known Member

    Feb 20, 2011
    Not always. It could be a tap, in which case it may be too small to give you a good output. You have to match it perfectly to suit your needs.
  6. tgotwalt1158


    Feb 28, 2011
    Do you mean without referring to diagram and PCB? If this is the case, even then you can find out the primary winding of a removed FBT. Look at the attached drawing. Its a typical FBT connection drawing. Note that there are three sections : 1) Primary, 2) Secondary HV, and 3) Secondary Grid Center tapped winding. By ohm meter on Rx10K you can single out primary as follows:
    Check any two ends which give indication of diode i.e. low resistance in one direction and the infinite resistance in other direction (One end in this case is always terminal under anode cap). That would be your HV secondary. Note it down or mark by a marker pen. Grid winding is simple to find since it has center tap. Just check by ohm meter three ends which show continuity mutually. The last left section will be your required primary winding.
    You can not find information about a particular FBT until you do not have its part no., since most are custom designed for their particular CRT. So, last resort is to check by the circuit diagram. For circuit diagram, try to find diagram for your IBM monitor from following link :

    • FBT.GIF
      File size:
      4.7 KB
    Last edited: Oct 20, 2011