LCD-TV repair

[PowerAmpFreak]

Re: LCD-TV repair

Digikey lists a JKL BF24438-33B, which ignites at 1400 volts and operates at 835 Volts, 5 mA. The 2500 volts you saw should be enough to get the CCFLs to ignite.

PlainBill

This will be simple enough to build, and be very handy when checking backlight panels in the future.

[PlainBill]

Re: LCD-TV repair

Ok, I get it
I think about building a small HV generator for CCFL testing purposes, what is the recommended operating voltage of a CCFL? And how much juice do I need to actually see something light up?

Digikey lists a JKL BF24438-33B, which ignites at 1400 volts and operates at 835 Volts, 5 mA. The 2500 volts you saw should be enough to get the CCFLs to ignite.

PlainBill

[PowerAmpFreak]

Re: LCD-TV repair

Think of it this way - capacitance is directly proportional to the overlapped area of the plates and inversely proportional to the distance between the plates. In my misspent youth I remember unwrapping paper caps - the layers were many feet long. In most capacitors the spacing is measured in thousandths of an inch. How much capacitance is there between 2 pinheads more than a foot apart?

PlainBill

Ok, I get it
I think about building a small HV generator for CCFL testing purposes, what is the recommended operating voltage of a CCFL? And how much juice do I need to actually see something light up?

[PlainBill]

Re: LCD-TV repair

The panel has two HV wires, each on either side of the panel. I believe there are several CCFL or EEFL's connected in parallell, so why shouldn't a few light if one or more were bad? Or their wires were loose.
It looks like one of the inputs has been disconnected so none of the lamps has contact with the HV supply.
By the way, is it possible to make a capacitance measurement across the lamps?

After the easter holiday I'll try to take some close pictures of the panel assembly and see if any of you might have a good idea how to get into the lamp compartment.

Think of it this way - capacitance is directly proportional to the overlapped area of the plates and inversely proportional to the distance between the plates. In my misspent youth I remember unwrapping paper caps - the layers were many feet long. In most capacitors the spacing is measured in thousandths of an inch. How much capacitance is there between 2 pinheads more than a foot apart?

PlainBill

[alexanna]

Re: LCD-TV repair

The panel has two HV wires, each on either side of the panel. I believe there are several CCFL or EEFL's connected in parallell, so why shouldn't a few light if one or more were bad? Or their wires were loose.
It looks like one of the inputs has been disconnected so none of the lamps has contact with the HV supply.
By the way, is it possible to make a capacitance measurement across the lamps?

After the easter holiday I'll try to take some close pictures of the panel assembly and see if any of you might have a good idea how to get into the lamp compartment.

Email ccflwarehouse and find out exactly what's inside your panel, then try to find similar CCFLs to substitute .They may be trying to light but you are unable to see them through the dark LCD panel

[PowerAmpFreak]

Re: LCD-TV repair

The panel has two HV wires, each on either side of the panel. I believe there are several CCFL or EEFL's connected in parallell, so why shouldn't a few light if one or more were bad? Or their wires were loose.
It looks like one of the inputs has been disconnected so none of the lamps has contact with the HV supply.
By the way, is it possible to make a capacitance measurement across the lamps?

After the easter holiday I'll try to take some close pictures of the panel assembly and see if any of you might have a good idea how to get into the lamp compartment.

[Th3_uN1Qu3]

Re: LCD-TV repair

Inside the panel, the connections to the lamps themselves.

[PowerAmpFreak]

Re: LCD-TV repair

No... but the wires going to the lamps can break, a few members here have found loose connections to otherwise good CCFLs.

Ok, you mean inside the panel or the wires from inverter to panel?

[Th3_uN1Qu3]

Re: LCD-TV repair

Is there any protection inside the panel, fuse or something that my go open if there's a CCFL failure?

No... but the wires going to the lamps can break, a few members here have found loose connections to otherwise good CCFLs.

[PowerAmpFreak]

Re: LCD-TV repair

2.5kV is strike voltage, if that doesn't drop off at all before the inverter shuts down, then it's definitely failed CCFLs.

I did the voltage measurements quick, since my oscilloscope probe is rated for 1500V peak but I was so curious so I give it a shot anyway.
I see no additional load on mains when inverter goes on, I would expect the power consumption to raise a bit if the CCFL were properly loading the inverter, but I cannot see this. Which also tells something is bad in the panel.
Is there any protection inside the panel, fuse or something that my go open if there's a CCFL failure?
It feels the HV goes into an open circuit.

[Th3_uN1Qu3]

Re: LCD-TV repair

2.5kV is strike voltage, if that doesn't drop off at all before the inverter shuts down, then it's definitely failed CCFLs.

[PowerAmpFreak]

Re: LCD-TV repair

I had failed ccfls on au-optronics panel (L/G) panel would light up for 2 seconds then shut down.
I first found a bad mosfet on slave inverter. and repaired that and it was working( the inverter).

The best thing I did is take another inverter board (one piece) powered off of 24vdc.

I knew it was good and the backlights did the same thing (2 seconds to black).

I then pulled the panel apart and found 3 bad ccfls.

Took them from another panel and soldered them in (some solder in and some push in).

Then I replaced them all (used) for color match.

Yes, I had the TV all in pieces trying to get into the panel itself and look for bad CCFL's, but I was forced to stop when I found that Samsung used steel rivets to put the panel assembly together and that the panel could be bought as a complete module $$$$, so appearently this will be very hard to repair. I've confirmed that both HV outputs generate voltages about 2.5kV, so I can only see the panel as the problem right now.

[cadiman]

Re: LCD-TV repair

I had failed ccfls on au-optronics panel (L/G) panel would light up for 2 seconds then shut down.
I first found a bad mosfet on slave inverter. and repaired that and it was working( the inverter).

The best thing I did is take another inverter board (one piece) powered off of 24vdc.

I knew it was good and the backlights did the same thing (2 seconds to black).

I then pulled the panel apart and found 3 bad ccfls.

Took them from another panel and soldered them in (some solder in and some push in).

Then I replaced them all (used) for color match.

[PowerAmpFreak]

Re: LCD-TV repair

Pain in the ass.

Hehe ... OK!
Yes - you're right, this has taken far too much time already

[Johnny P]

Re: LCD-TV repair

Pain in the ass.

[PowerAmpFreak]

Re: LCD-TV repair

Right, as long as the values are the same. What a PITA!

PITA? Hmm...

[Johnny P]

Re: LCD-TV repair

Right, as long as the values are the same. What a PITA!

[PowerAmpFreak]

Re: LCD-TV repair

There is no way to simulate the load of the lamps? Then the inverter board should remain on. Just an assumption mind you.

It's a good idea, but the load of the lamps seems to be purely capacitive and I don't know if this actually could be substituted by a resistive load. But one thing I might try is to power up another backlight (on another tv) with this inverter and see what happens. Then I could swap it all around and power the problematic panel with a known good inverter.

[Johnny P]

Re: LCD-TV repair

There is no way to simulate the load of the lamps? Then the inverter board should remain on. Just an assumption mind you.

[PowerAmpFreak]

Re: LCD-TV repair

Thanks guys, but of course I have the datasheet for the '9882 but no schematics of the inverter.