Instructables

Current limiting high voltage - ccfl inverter help ?

Okay as my first question i'll say hi first , and Darren from Ireland here , fair "know how" of electronics and how things roughly work.

I have a 32inch TV who's inverter board is toast (okay its going on and off straight away) , I know its getting power from the psu board as there is little or no voltage drop when I flip the TV on and the lights fire up.

I have asked 3 people at work (Electro techs at work) and they all say the same thing , replace the board , its too much work (I think there just lazy) and also they all say they would need the data sheet on all components or the circuit diagram.

So well me with my stupid head wants to try and have a stab and getting a free TV.

So I have ordered a CCFL inverter power source for a neon case light , which I intend to use just to see if any one bulb is gone as im not sure if that is what could be kickin the inverter off.

And the other thing i have ordered is a "Universal inverter for 10-30v 4 bulb 17-24inch" from ebay.

So the question is , if one bulb is gone and well i doubt i can order a bulb like this and replace as that would be end of tv if i open than panel . is there a way to simulate that bulb working in any way to stop the inverter going off because of one bulb.

And the other question is , if I want to use this universal inverter , what is causing it too be a 17-24 inch only ?

From what I understand is if I am wrong correct me please , that the larger bulb would burn the driver chips/fet's drawing too much current.

So would there be a easy / safe way to just limit the out put so they will run but a little dim (as the tv is intended to be used in a dark room any way)

Any ideas welcome , and for what ever comes up , Thanks !

evilad1 year ago
You might be in luck. You say the backlight comes on for a couple of seconds when you first turn on the TV? This is often a sign that the driver IC is flagging a fault condition, usually because one of the ccfl tubes is faulty.

You could test this by finding the datasheet for the IC and trying to override the fault condition. In my case it was bypassing a capacitor to ground so that the 2-second shutdown timer became an infinite second shutdown timer.

If this allows your backlight to stay on then it is probably as I said before. BE WARNED however, this will eventually damage something.

The faulty ccfl could be old or, as in my case, one of the wires going into the tube had become detached from excessive charring caused by arcing. You could replace the tube or simply try resoldering the wire. I had to replace a small length of wire to achieve this.

Also note that, I think I'm right in saying, the charring only occurs on the return side of the tube and so you shouldn't need a thickly insulated wire to handle high-voltages, but see what is already in use.

Your driver board won't like it if you simply unplug the faulty tube. Additionally bypassing it with a capacitor or resistor is going to create a lot of heat somewhere and so is also a bad idea.

Final warning. An open monitor probably has exposed mains voltages as well as high-voltages for the tubes. Keep hands away and don't be working on a metal tray. If you're not sure, take the minimum of precaution of standing well back with a remote power switch.
dwoods-1 (author)  evilad1 year ago
Thank you very much , but I gave up , the universal inverter blew as they had a RED ground and a BLACK v+ ...in haste i blew it.

Also those Driver IC's well there not to be found they have no data sheet i can find.

Even the company who made the board came back with a "sorry we can not give you any details on this board due to contractual obligations"

In the end i did this , running off 1.5a 12v and it looks great here are some pic's

http://imageshack.us/a/img15/1217/imag0248k.jpg

http://imageshack.us/a/img594/9703/imag0249x.jpg

http://imageshack.us/a/img402/103/imag0251au.jpg

http://imageshack.us/a/img13/3092/imag0254k.jpg

But again thanks for the advice , Next time I have a TV like this though I honestly think for 20 euros for those led's its a much better option.
Jayefuu1 year ago
It might also help to list the TV make and model and a link to a teardown on ifixit.com so people can help you.