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

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=-
Remove these ads by Signing Up

## 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 :

## Step 2: How to find the pins location of the primary coil?

With a simple ohmeter this is very simple, you will find easily the primary inputs because the coil resistance is about 1 ohm
Bumba Lodh3 years ago
i don't have 24 volts dc power supply but i've 12 volts dc power supply
Jimmy Proton (author)  Bumba Lodh3 years ago
That might work, if it does then you should see around 3 volts on your meter.
3 days ago

crazy-blender1 year ago
What multimeter is that it seems that everybody has that multimeter
3 days ago

If you can read it is NG60... :)

trekman3 years ago
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)  trekman3 years ago
flybacks often have more than one primary, use whichever one you like.
1 year ago
what if you use multiple primaries?
abhilash4761 year ago
i could not find the primary and secondary pins/.........
a2262632 years ago
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?
2 years ago
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
2 years ago
Alrighty. Will do. Thanks!
2 years ago