Testing CCFLs

[OldLes]

The saga continues, but more confusion.
As stated earlier, this inverter board will fire up the two CCFLs which are series connected as in my sketch.
The off load voltage is 8,200 V pp (3,900V rms), falling to 3,100V pp (1,095V rms). The tubes from the Toshiba 23" LCD measure 20" each, so I expect it to light up the 28" tube from a 32" LCD, and the 35" tube from the 42" LCD.
Not so!  Once again, just some excitation at the ends, but no proper illumination. I really can't explain this; I even tried linking two sections in the hope of increasing the output level, as I did with the Samsung inverter earlier, but no luck this time.
Oh well! At least I have two testers for shorter length CCFLs.
The search continues.
Les.

[Keith]

Hi Les,

What have you done to overcome the protection circuits?

Keith

[OldLes]

Kieth, for the Samsung inverter, see my earlier post. I supplied +12V to the supply pins (10,11 and 12), and  the -12V to pins 1,3,5,6,8 and 9. I then connected the +12v through a 10K resistor to the pin4, which fired up the inverter for about 2 seconds, plenty of time if the CCFL is OK.

For the 23" Toshiba's inverter (LG-Phillips manufacture), I connected it exactly as shown in the sketch I made (LC-230W01-opn_1.pdf  --See earlier) Pressing the push button switch, holding and then releasing  runs the inverter for about 900mS, again enough time for a good CCFL. You will see from the sketch that pin 8 needs to be held at ground, with pin 7 somewhere between 1V and 5V, hence choice of 3V3 zener. The fact that it will fire two 23" CCFLs in series, but NOT a 32" or 42" confuses me.
As somebody else once said, "I will be back"!
Help gratefully accepted.
Les.

[Keith]

The reason they dont stay on is because the protection is activating. Download the data sheet for the control chip to find the  protection pins.

Keith

[OldLes]

Kieth, sorry, I misunderstood your question.
Problem is I don't have a circuit for the LG-Phillips board. It has six pairs of HV transformers, powering through six connectors, the 12 CCFLs (made from twos in series).
They are divided up into three sections (thus four CCFLs per section) each with a BIT3106, presumably "in control". Any suggestions?
When I first got it working, I had a 3k3 resistor where I now have the 3v3 zener. It then needed the push button pressing, then releasing. The CCFLs would light, and generally STAY on, until I BRIEFLY pressed the push switch again. Maybe playing around with values would help. Possibly using a resistor (4K7??) in parallel with the zener? However, if the CCFL is good, I think the ON time is OK.
Les.

[Keith]

Hi Les,

Just download the data sheet for the BIT3106, you can then try different ways of bypassing the protection. It is preferable to use a board with only 1 control chip and several drivers, as you will have to bypass each chip.

Try to find a board using an OZ694 type chip.

Keith

[Keith]

Les,

Finally my CCFL tester arrived from Singapore, it has had a nice trip around the world to get here! A few quick tests and it will light 300mm, 900mm from a 40" screen and a U shaped from a 26" that is 1200mm full length. To be honest it is much easier and quicker to use than a modded board and for a tenner well worth it. Also safer than a modded board, with all that HV waiting to bite you.

Ebay item 150948891826

Keith

[OldLes]

Kieth, I have not given up on trying different methods yet, but I have taken the hint.
Unit just ordered. Very busy on the 'bike right now, so whether or not I "play" any more before the tester arrives, we shall see.
Les.

[Keith]

Hi Les,

You will need to check the croc clip on the ground lead, it will probably need soldering as it is just poorly crimped.

I don't fix many TVs, mostly other electronic or electrical items, but this little tester will make it easier to test the lamps.

Keith

[OldLes]

Well, my little tester arrived last week, and I found time to play with it this afternoon. (Kieth, quite right, the croc clip needs soldering to get continuity. Other than that it seems well put together). I tried the three suspect tubes I removed from the 42" Sharp, and of course they tested out OK!!!!
I also checked the tubes in the 32" sharp sitting patiently on the bench, and all seem OK, but not as easy to test in the set as loose on the bench. I want to test a few more, preferably some known (definitely!!!!) faulty ones, as well as more of all sizes.
I have powered it from my bench supply, at the stipulated 12v, and it seems to draw current according to the tube length, but too soon to be definitive.
Les.