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Low Cost CCFL Tester Article By Gerry Of GM Computing UK

By on June 18, 2010

Below is an article provided by Gerry and if you have any question you can click on the comment link below.

A CCFL tester for laptop and monitor backlight tubes could in principal be made from any inverter designed to provide an appropriate output voltage of around 700v. A laptop inverter seems ideal since it is very small and cheap to buy. Unfortunately, in addition to the appropriate DC power supply, it needs appropriate control signals before it will turn on, which are provided by the computer. To simulate these control signals in a tester would be complex. However, CCFL are also used in decorative applications, and inverters made for such use simply produce a suitable output voltage when 12v input is provided. Such an inverter is designed for PC case neons; these are available for low prices on Ebay. See for example this seller, who includes the cabling and switch for about £3.50 all-in:


Each Lot Contains:

One dual output inverter box

Input wiring for the inverter with; switch, and 4 pin molex pass through at one end, and two pin inverter connection at the other.

Product Specifications:

Dual, two pin output inverter, with single 2 pin input

Total 12v wiring length approx: 50cm, unlooped

Low current draw of 5.0mA

Inline rocker switch, and 4 pin molex connection with pass through

Output voltage: 680v

Input voltage: 12V DC

Quality Specifications:

ISO 9001:2000 certified factory

CE compliant

 ccfl tester

The next picture shows the inverter with the top removed – this is done by carefully sliding a thin knife blade round the joint. You will see the two sockets for two CCFL tubes. You will also see that these are not the correct sockets for either laptop CCFL tubes (small socket) or TFT Monitor CCFL tubes (small or large socket).

 backlight tester

However, one or both of the incorrect sockets may easily be replaced by a socket from a laptop inverter – to do this you will need a “dead” laptop inverter from which to obtain the socket (note that some TFT monitors also use the small socket).


Unfortunately, there is not room to replace one of the incorrect sockets with the correct large socket. However, an adapter for the small socket is easily made; once again you will need a dead TFT monitor inverter board to obtain the large socket and a dead CCFL tube from a laptop for the plug.



Alternatively, of course, if you can obtain plugs that fit the original inverter sockets, you can make up adaptors for both laptop small sockets and monitor large sockets.


The final part of the tester is the 12v DC power required by the inverter. You can provide this from a PC power supply which has the required molex plugs. This worked fine, but they are large and heavy. I thought a stand alone power supply as used by hard disk adapters, would be preferable which are very cheap on Ebay – as shown in the picture.



Unfortunately I found that these do not seem to provide any output until a significant load is applied. The startup characteristic of the inverter does not seem to do this. For test purposes I have used a Lab power supply, where voltage and current can be closely controlled. The picture illustrates a 14″ CCFL tube (from a Compaq Evo N600C) fired up by the inverter. You will see the voltage is 12v with 0.49 amps current – the tube is rated at 7w I believe so it is under-running slightly.


 lamp tester

The tester seems to do the job, but I have only tried it with 14″ and 15″ tubes. The next task will be to mount the inverter PCB in a larger case with its own power supply.


GM Computing





Note: To all readers- if you have any interesting repair articles that you need to share with others you can send it to me at jestineyong (at) I will look into the article and if it suitable and have good info i will post it into my blog with your name signature just like the one above-thanks!





  1. janaka

    June 18, 2010 at 3:17 am

    attach video clip how to properly do it then useful sale that divices

  2. beh

    June 19, 2010 at 7:10 am

    yes . a practical diagram of a ccfl tester is also useful for me hope to get this

  3. Daniel F

    September 24, 2010 at 6:44 pm

    I wonder how useful this really is?

    I recently had a problem with a dell 15" monitor blinking on and off.
    I first removed the 4 ccfls, plugged each one into my old IBM Thinkpad T23 laptop inverter and they all powered up.

    However, they were all very black at the ends of the ccfl and also one of the ccfls was not very bright at one end.

    Because the above tester and my laptops inverter has no feedback circuit is it not likely that a failing ccfl would appear to be okay via this method but when plugged back into the dell monitor utilizing a feedback circuit the ccfls may then cause the blinking.

    In other words, the only real way I believe to check whether ccfls are causing a monitor fault is to swap them for new ones.

    Please correct me if I'm wrong.

    Daniel F

  4. admin

    September 24, 2010 at 10:19 pm

    Hi Daniel,

    Yes you are right. Swap the lamp unless you have a ccfl tester.


  5. Amir Mukhtar

    February 18, 2011 at 6:32 am

    Sir Jestine,

    I want to make CCFL tube tester. kindly help me and guide me in order to make CCFL Tester. Could it posible to provide me circuit diagram.i will make and guide to others.

    thanks you
    amir mukhtar

  6. admin

    February 18, 2011 at 8:49 am

    HI Amir,

    I wish to build one too but at current moment have not found any circuit yet.


  7. RK Murthy Challa

    September 19, 2012 at 12:51 pm

    Can U plz  mail  me the circuit diagram of low cost  CCFL Tester ( only Inverter ckt) . I shall be be thankful to U

    • Jestine Yong

      September 20, 2012 at 8:06 pm

      Hi RK,

      Sorry I do not have the schematic diagram.



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