920NW 2 seconds backlight then off

[paulstef]

Power supply is good. voltages stable. The CCFL chip turns off because when TIMER (pin3) ramps up to 3V VSENS is lower than 3V. As described on page 6 of the datasheet of the chip: http://monitor.espec.ws/files/oz9938_140.pdf

VSENS goes up to 1V max, therefore I assume the high voltage is about 1.5kV (?)

Question : Can this be caused by a defective CCFL and if so did anyone disable this protection or modify the circuit to use it anyway? I mean I do have backlight for 2 seconds...

manual: http://galaxybrain.ru/files/Samsung_...ster_920NW.pdf



Frankly I do not know how CCFLs usually behave when they are damaged.

[selldoor]

Re: 920NW 2 seconds backlight then off

Do you have any spare bulbs -another monitor- even a dead laptop.
Can you make a or a couple of test bulbs from cfl - see in Budms signature


EDIT have you done other tests in the 2 seconds to black guide at the top of this forum

[paulstef]

Re: 920NW 2 seconds backlight then off

Do you have any spare bulbs -another monitor- even a dead laptop.
Can you make a or a couple of test bulbs from cfl - see in Budms signature

I may try that... Not really keen to replace bulbs though. :-/

[paulstef]

Re: 920NW 2 seconds backlight then off

@selldoor, you mentioned the Budm signature link but as far as I can see he used CFLs? Since here it seems I have about 1.5kV does that mean I have CCFLs? Or how could I be sure?

I'm assuming a CFL would have a low resistance due to the filament, is that right?

What do they use in LCD TVs? I have several lying around with cracked screens... But what about their wattage?

[budm]

Re: 920NW 2 seconds backlight then off

The filament of the CFL is not being used to heat up the CFL, it is used to supply the connection only, the high voltage from the inverter is high enough to excite the CFL.

[paulstef]

Re: 920NW 2 seconds backlight then off

The filament of the CFL is not being used to heat up the CFL, it is used to supply the connection only, the high voltage from the inverter is high enough to excite the CFL.

Do CFL and CCFL work with different voltages? I read the filament in the CFL heats up to 900F, and to 200F in the CCFL.

If I take any other bulb as suggested by selldoor and take a CCFL instead of a CFL by mistake will I blow up anything else?

I thought TVs use CCFL not CFL as backlight...

[budm]

Re: 920NW 2 seconds backlight then off

CFL needs to have the filament heat up to start the conduction, the CCFL use really the high Voltage to start the conduction.
LCD TV and monitor use CCFL, CFL is only used home lights.
Like I said we are not using the filament in the CFL, the filament is being as an electrode for the high voltage for the test lamp.
https://www.badcaps.net/forum/showth...er+testing+cfl

[selldoor]

Re: 920NW 2 seconds backlight then off

Monitor has ccfl if you can find a broken tv with 18-20 inch screen or less
you could try the tubes. Bigger will probably be too big and damage the
inverter transformers.
Sometimes EEFL bulbs are used.

The CFL is only a temporary test bulb you do not need to think about it, just make one and try it.

It does not work the same as when it is a cfl bulb the filaments do not need to heat. Really you are just using the actual fluorescent tube bit- when you connect the inverter transformer it just causes the bulb to fluoresce.

[paulstef]

Re: 920NW 2 seconds backlight then off

Hum, I only have +42" LCDs.

I assume this test is to determine if CCFL or inverter is the culprit?

[budm]

Re: 920NW 2 seconds backlight then off

The use of the two test lamps is to find out if you have inverter problem or the lamps problem, it saves me lots of troubleshooting times.