General question about CCFL backlight

[rtstorm]

Hello, i have one small monitor that have 2 CCFL backlight. Problem is that lamps wont turn on. Tha monitor use external psu with 12V.

I check caps and thay are ok, the inverter board receive 12V but when starting that it drop to 10.8V

I test lamp with external ccfl tester one by one and they turn on.

How can i be shure that lamp are ok or defective?

Interesting thing is when i connect 3rd lamp (external lamp) to the existing two they all turn on and stay on for 10 seconds and then turn off again.

I think that lamps are bad but how can be sure? What is normal lamp current?

[Joe Black]

Re: General question about CCFL backlight

Well, neighbour, since your lamps turn on eventually, they are obviously good.

You have a bad inverter. Post pictures of your board(s)...

You would typically search for shorted transistors, check transformators drivers, and transformators themselves... Of course, caps as always...

[stj]

Re: General question about CCFL backlight

your psu is weak - the 12v should not drop.
if the invertor draws too much current it should blow the onboard fuse.

check your psu.

[rtstorm]

Re: General question about CCFL backlight

I have external PSU, i can increse the voltage up to 30V

I will try with 15-16V

[rtstorm]

Re: General question about CCFL backlight

Well i increse voltage to 14V and backlight working

I do not understand how 12V is not enought when the monitor have a label on backside tjat say 12V input

[stj]

Re: General question about CCFL backlight

12v is not the problem, your not feeding enough amps.

[rtstorm]

Re: General question about CCFL backlight

Hmm but my Power supply have 3A rail. When i set oitput to 12V and backlight try to turn on the monitor pull 1.4A and then drop to 0.6A

But when set to 14V monitor pull 1.6A and stay on, does not make sense to me.

[stj]

Re: General question about CCFL backlight

sorry, but if a 3a suppy drops to 10.8 when you give it a 1.6A load then something is not right - either a connector or the psu is not doing it's job.

if you set the psu to 14v is it still 14v at the invertor when running, or are you still seeing a 1.2v drop?

[rtstorm]

Re: General question about CCFL backlight

When i set psu to 14V i have 13.5V on inverter in stand by and when turn on LCD it drop to 11.5V

[stj]

Re: General question about CCFL backlight

then check the voltage at the psu, because you need to trace the drop.

[budm]

Re: General question about CCFL backlight

Are you using SMPS regulated 12V (4A TYP.) power supply?

[stj]

Re: General question about CCFL backlight

it sounds like he's using a lab supply

[rtstorm]

Re: General question about CCFL backlight

Yes i am using lab power supply

[stj]

Re: General question about CCFL backlight

are you seeing the voltdrop on the psu terminals?

[rtstorm]

Re: General question about CCFL backlight

I will check but i think not.

[jiroy]

Re: General question about CCFL backlight

If this small monitor is for desktops use only , you can always take 12 volts directly from the desktop PSU . Most of those PS provide 10 A at 12 volts .

Less headaches concerning monitors power supplies .

[rtstorm]

Re: General question about CCFL backlight

Well i check there is no voltage drop on my lab power supply

[rtstorm]

Re: General question about CCFL backlight

Here is the picture of main board and inverter

[budm]

Re: General question about CCFL backlight

I think you lab power supply does not capability to handle the in inrush current otherwise you will not see the Voltage drops like that.

[stj]

Re: General question about CCFL backlight

it's probably the wires, those croc clips and the wires they are clipped on are not suitable.