How are inverter boards controlled ?

[120volts]

Hi I'm new to the Badcaps forum.

I took a four years coarse in electronics at a tech trade school and then worked for over fifteen years for various companies as a bench tech.

Here's my question.

On the typical CCFL backlight inverter board how is the brightness controlled?

Is it by raising or lowering the control voltage or is it controlled by varying pulse width?

[tom66]

Re: How are inverter boards controlled ?

The DIM signal an analog voltage typically from 0 - 3.3V which controls brightness from approx 10% to 100%, or a PWM signal (pulse width modulation.)

Note minimum brightness around 10% for CCFL because they cannot go below that without having to re-ignite which takes about a second to occur.

[120volts]

Re: How are inverter boards controlled ?

Thanks for the replay Tom.
Time to get the scope up and running.

[120volts]

Re: How are inverter boards controlled ?

Ok, when I turn on this DX-LCD32-09 Dynex I get sound but back-light for only 1 sec.

The inverter board is getting the 24V and 5V. and on the PWM I get a steady +3.4V
with the scope I don't see any pulse or frequency at all.

[budm]

Re: How are inverter boards controlled ?

That is the 2-second to black problem which can be the MOSFET, Inverter transformer, CCFL, etc.
https://www.badcaps.net/forum/showthread.php?t=10419

[120volts]

Re: How are inverter boards controlled ?

OK thanks for the links but, my question was should I be seeing a control pulse?
I bought a used inverter board and was told it was working 100% and the TV still has the same problem.

[budm]

Re: How are inverter boards controlled ?

The PWM is about 200Hz. But does it also has another connection for the analog dimming? Set your meter to AC to see if you will get any AC voltage. Board P/N?
Is this the board, which only has PWM only.
http://www.shopjimmy.com/vit68001-95...t-inverter.htm
According to what I found about your LCD panel spec, the PWM can be fed with Anolag signal.
https://cdn.badcaps-static.com/pdfs/...4256d2d602.pdf
3.3VDC = Max brightness. If this is the panel you have.

[tom66]

Re: How are inverter boards controlled ?

You probably have "2 seconds to black". This occurs when the set detects an open or shorted bulb in the panel, which causes it to shut down after the ignition phase (2 seconds.)

[budm]

Re: How are inverter boards controlled ?

I agree.