# How to find the primary and the secondary coils of a FlyBack transformer

3 Steps
The main problem, in most cases, is that you don't know the pinout diagram of a flyback transformer. So, I shall try to give you a simple method to find the primary coil input pins and also the 0 V output pin of the HV secondary coil.

-=I do not take full credit for this=-
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## Step 1: How to find the 0 V pin connection of the secundary coil?

With a common digital ohmeter it is impossible to find the secondary coil pinout because its resistance is much too high. The main HV output is simple to find : this is the big red cable with the suction cup, but you need to find the 0 V pin of the secondary coil on the flyback transformer. So, I give you a simple method to find this 0v pin :

a) You need a 24 V DC power supply and a digital voltmeter set in 20 V range. Connect the + input of your voltmeter to the THT ouput plug ( in the suction cup ) and the (-) to the 0V of your power supply. Then, with the +24V output from your power supply, test each pin of your flyback transformer. When you measure a voltage between 5 and 10 V you have found the 0 V pin of your secondary coil. This is very simple... Look at the diagram and the photo below :
abhilash476 says: May 21, 2013. 2:39 AM
i could not find the primary and secondary pins/.........
crazy-blender says: Mar 30, 2013. 6:13 AM
What multimeter is that it seems that everybody has that multimeter
a226263 says: Jul 4, 2012. 11:12 AM
I'm trying to find the pins to the primary coil. I bought a new flyback a couple of weeks ago. My flyback has 10 pins. I got these results:

Pins ..... Resistance
1 + 5 .... 2 ohms
1 + 9 .... 1.8 ohms
5 + 9 .... 0.9 ohms

2 + 8 .... 0.9 ohms

3 + 4 .... 0.8 ohms
3 + 6 .... 0.8 ohms
4 + 6 .... 0.6 ohms
All the other combinations (i.e; pins 1 + 3) produced no resistance, so that means that pins 1 + 3 are not connected. Conversely, this means that pins 1+5+9 are connected; pins 2+8 are connected; pins 3+4+6 are connected; and pin 7 and pin 10 are not connected to any other pins.

The first problem is that many of these gave me a resistance close to 1 ohm, so I still don't know which pins to use for the primary coil.
The second problem is that a flyback should have two sets of connected pins; pins that connect to the primary coil, and pins the connect to the secondary coil. However, I seem to have 3 sets of connected pins (or five sets, depending on how you count). Does this mean something is disconnected inside my flyback?

I didn't know what to do, so I just went ahead and connected it to the CFL circuit. I tried pins 5+9, 2+8, and 3+4 as the pins to the primary coil, along with every combination of the 4 pins on the CFL circuit, but did not get a single arc for any of them. Does this mean that my brand-new flyback is bad?
crazy-blender in reply to a226263Jul 17, 2012. 5:47 PM
it might be bad double check with each set of pins and if it still does not work buy another flyback and see if it works
a226263 in reply to crazy-blenderJul 17, 2012. 10:38 PM
Alrighty. Will do. Thanks!
crazy-blender in reply to a226263Jul 18, 2012. 6:12 AM
crazy-blender says: Jul 17, 2012. 5:44 PM
will a 9 volt battery work for finding the primary and secondary coils ?
R.A.T.M says: Feb 7, 2012. 7:29 PM
so i know what the main THT out put is but i have 3 other wires hanging about what are they 4
geckomage says: Oct 25, 2011. 6:09 AM
hey man, ive been searching and searching on how to find these and everyone always gave some far out crazy ways that i could not get to work. but yours has. so i would like to thank you! :) with a continuity meter i found that there were 2 pins with no matches (one turned out to be hv ground) then 3 pins with matches. 2 of those made the 1 ohm resistance thing for the primary coil. and then 7 pins all seemingly connected together with about a half ohm of resistance between them all. if you could explain what that is it'd be appreciated. also i couldnt get my slow volt meter to read a spike of 30ish v. but i did get it to read about 13-15 with a 9 volt battery pulsing it. and the other polarity got like .3v or somethin. so i'd say i found a winner ;) ima make a driver now and hope i dont blow up my transistors. haha. thanks so much! :) i wish you the best of luck in all your endeavors.
Bumba Lodh says: Sep 7, 2011. 5:54 AM
i don't have 24 volts dc power supply but i've 12 volts dc power supply
Jimmy Proton (author) in reply to Bumba LodhSep 7, 2011. 8:14 PM
That might work, if it does then you should see around 3 volts on your meter.
Rbwood says: Aug 16, 2011. 1:15 PM
I have to say thank you so much! Your instructions are the one and only set of directions that actually worked for me. Thank You.
Jimmy Proton (author) in reply to RbwoodAug 16, 2011. 10:16 PM
Your welcome but i do not take full credit for these.
ARJOON says: Feb 1, 2011. 1:25 AM
don't forget guys. ac from wall socket will not work. frequency is too low.
trekman says: Dec 28, 2010. 2:27 PM
The fly back transformer I have came from a 19” TV. I followed the instructions and found the 0 V pin and tested for the 2 primary pins. I got very low reading using a 9 volt battery. I happened to have a 9 volt A/C adaptor but the output was 9 volt A/C so I used that to find the primary coil pins. The thing is I found 2 sets of 2 pins that give me 35.5 and 34.7 volts output. Pines 9 and 10 also pins 10 and 1 give almost the same output. Which 2 should I use? This reading is on the A/C scale on my VOM. Using a 9 volt battery I was only able to get 3 to 4 volt reading.

Thanks for any help.
Tom
Jimmy Proton (author) in reply to trekmanDec 28, 2010. 4:30 PM
flybacks often have more than one primary, use whichever one you like.