Low Cost CCFL Tester Article By Gerry Of GM Computing UK
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:
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.
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
ISO 9001:2000 certified factory
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).
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.
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.
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