Lilliput 7inch ccfl problems

**marc456** · 05-08-2006, 03:05 PM

Not posted here for quite a while but am having a nightmare with my lilliput (nothing unusual about that!)

The backlight isnt working, i can see a picture on the screen so I know the lcd is ok, but my question is how can I find out if its the inverter or the lamp. I have measured the voltage on the inverter output but my equipment is limited, I used a potentail divider of 18.8Mohms and 200k as they are the biggest resistors I have. The voltage seems to be about 6.3Vac for about 5seconds then drops down to 0 (this equates to about 600Vac) but is this inverter going to drive 2000V across 19Mohms? also I thought that the voltage should be about 1000V under normal conditions once the thing had started or do I have that wrong?

If anyone can let me know of another way to approach this that would be even better.

If it is the backlight tube how easy is it to change it along with a dimmable inverter? as the lcd is perfect for what i need.

Please help! very worried carputer user :-(

Thanks

Marc

**marc456** · 05-22-2006, 05:10 PM

OK, well I have got my oscillascope out to check all the outputs from the inverter but I am getting slightly unusual results to say the least.

I am getting a good 60KHz sine wave at startup but after about 3 seconds it goes to nothing, now when the tube is attached there is no glimmer or anything. The voltage reading is strange as I am not getting consistent results with my equipment. But I will get there.

Now my question is this, does a ccfl tube just blow never to work again?

I have found that RS do a 380mm tube thats 3mm thick, however finding an inverter that fits the Voltage and current requirements is an absolute nightmare.
The tube out of the lilliput is 400mm x 2.5mm but begers can't be choosers.

Anyone know of an inverter that can power the lilliput ccfl tube, I have already removed it thinking that was the problem but now im not so sure.

Marc

**marc456** · 05-22-2006, 06:10 PM

I have two questions, Should an inverter get too hot too touch? and secondly does anyone know what the pins are for the inverter transformer itself?

I have the same inverter as this digitalww picture shows.

http://www.digitalww.com/Lilliput_to...ller_front.JPG

Just to avoid any confusion.

I have tried looking for it on the net to no avail.

marc

**spmclaugh** · 05-23-2006, 11:34 AM

First post for me in a long time...

A CCFL tube could "blow" as you say, if the glass had a pinhole in it and the gas escaped. Also, I guess the electrode could become electrically disconnected, though usually they degrade slowly over time (due to chemical reactions with the particular gasses used). Some fluorescent tubes have incandescent-type filaments to "heat" the tube in cold conditions, but I'm guessing that has nothing to do with this.

But by the way, if it is the tube, most inverters automatically sense an open circuit (dead tube) condition and shut themselves off. I would think that they would take way less than 3 seconds to do this (my naive guess would be on the order of 10's of "dead" cycles).

If you want to test whether the tube still has gas in it, hold it next to a high-power transformer (city power lines) or microwave transmitter (I don't know if I recommend the latter though, especially sticking it in the microwave, because you may destroy the tube and cause other damage). Some high power RF radios can excite the tube by "keying" on the transmitter. Or if you have access to another inverter, that's the easy test.