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Testing CCFLs

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OldLes:
I tried the samsung inverter for real this morning, but I only had CCFLs from 32" and 40" sets.
The "standard" output (950v rms off load) did nothing whatever on either size of tube.
Trying the two high level outputs in series as explained yesterday (2760v rms off load) succeeded in lighting up both ends, perhaps a little over 1/3rd of the length, but the centre 1/3rd remained unlit. Same for 32" and 40" set CCFLs.
I did try varying the supply up to about 14v, but saw no significant change.
I will keep this for shorter CCFLs, and try something else for longer ones.

I have the two inverter modules from a JVC set I scrapped (cracked LCD panel) for which I need info, but will open a separate thread for that.
Les.

OldLes:
I pulled the CCFLs from a Toshiba 23WL46B, which turn out to me two tubes in series, so effectively equivalent to a 46" set's CCFL.
Once more, the Samsung inverter would not light them up, BUT, using the two outputs in series as mentioned, I could get one half to light up perfectly. The off load level of 7,200vpp fell to 2,450vpp (approx 865v rms), with the original sine waveform now distorting during its rising period. The current passed was 5.5mA. The supply current increased from 0.4A quiescent (no CCFL connected) to 1.25A, suggesting a 50% conversion efficiency. Now I just need to light the full length of the two tubes.
I have the inverter board from the Toshiba, but so far can't persuade it to produce any output.
I will search for a circuit for that next.
Les.

sabre504:
Hi Les
assuming i have the right ones these may help

OldLes:
Sabre, thanks for that. It seems to be generic sheet covering panel and inverter, but there is a difference with my inverter. Mine has pins 4, 5 and 6 with no connection. I have tried feeding supply via 10K and 22K to both pin 7 (yellow) and pin 8 (White), so far with no response. Maybe further study of this will lead to a result.
I know it is OK, as I tested it out 5 mins before dismantling. It had one vertical line on screen, but backlights etc were good.
Les.

OldLes:
A bit more study of Sabre's info has lead me to the simple circuit attached. It will now fire up the two series connected CCFLs, so should be OK for the 42" set I need to test out the individual CCFLs before replacement.
These inverter boards seem to be quite common, so maybe they could be OK for others to use.
I may change the 2K2 resistor for a 3.3V zener, and may need minor changes to get it to switch off consistently. This could allow the supply voltage to be reduced for smaller CCFL tubes.
I will measure the off load and on load voltages as well as the current thro the tube.
Circuit now modified. Test results will follow.
Les

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