Testing: replace a backlight with a resistor ?

[rb0746]

I would like to prove that a backlight on an lcd screen is good or bad

what size resistor would I use to fool the inverters safety shut-off ?


I have tried a 200 ohm 5 watt last for about 8-10 seconds.

Unfortunately I don't have any more resistors to try. I was hoping someone that has traveled this road before me will share what resistor or resistors worked for this application .

[rb0746]

Re: Testing: replace a backlight with a resistor ?

Okay problem solved !


Thanks to PlainBill , OHM's Law and fortitude.


We need more people like PlainBill

[seanc]

Re: Testing: replace a backlight with a resistor ?

Care to post/link the results here for others to benefit?

[rb0746]

Re: Testing: replace a backlight with a resistor ?

Care to post/link the results here for others to benefit?

as per PlainBill
Ohms law. At a rough guess a CCFL runs at 650 - 1000 Volts and draws 3-5 mA.

E / I = R or 800/.004 = 200Kohms

I X E = P or .004 X 800 = 3.2 watts

So a 200K ohm, 5 watt resistor hooked to an appropriate connector should do it. Probably be a good idea to use a resistor rated for high voltage.

No warranty at this price.

Now, I've been thinking it should be possible to do something similar, except use two resistors (180K, 20K) in series to form a voltage divider so you could actually measure the output voltage without frying a DMM.

PlainBill




This works perfectly !


Thanks again PlainBill

[rb0746]

Re: Testing: replace a backlight with a resistor ?

I would like to prove that a backlight on an lcd screen is good or bad

what size resistor would I use to fool the inverters safety shut-off ?


I have tried a 200 ohm 5 watt last for about 8-10 seconds.

Unfortunately I don't have any more resistors to try. I was hoping someone that has traveled this road before me will share what resistor or resistors worked for this application .

It was my bad I did not make sure I had an input at the time of testing because of this the set did what it should have. 8-10 sec. then backlight off. After hooking up a dvd to the set it worked as planned without a backlight .So as you see it is possible to run with a burnt out backlight ...... if you use OHM's Law of course . !