HannsG Monitor Repair!

[Ohmzilla]

Greetings! I have an old 22-inch HannsG that has worked faithfully as a security screen for years. (On 24/7 365)

Couple days ago it started to come on for 3-5 second and then the backlight would go out, I could still see a picture if I illuminated the screen with a LED flashlight.

I pulled it apart and changed the two caps that looked suspect the others visually looked fine. No change, power on 3-5 secs and the backlight would turn off

Being a newbie in electronics repair, is it possible for a capacitor to fail internally and show no outward signs?

Thanks!

[PA0PBZ]

It's most likely the backlight tubes, available on EBay if you take the right measurements (thickness and length).

[Ohmzilla]

It's most likely the backlight tubes, available on EBay if you take the right measurements (thickness and length).

Is there a way to check this? I have not been able to find a data sheet on the monitor. It is the hi221d

Thanks!

[PA0PBZ]

The only way to check if it is the CCFL tubes is to replace them and see if it solves the problem. Sorry but there is no way you can measure it. The fact that it runs fine for a few seconds seems to indicate that the inverter is still doing its job so there's no major failure there. If you can take the screen apart and look at the CCFL tubes you can probably see they are darkened at the ends, which is a good indication that they are end of life. My experience is that with this kind of failure mode it is most likely the tubes, but of course it's not a 100% guarantee. If you want to solve it the easy way just throw away the monitor and get a new one 

[Ohmzilla]

It was more of my first real project, I have a bench supply I was hoping there was a way to power em up to see. Just looking around I realize now they are pretty high voltage to start and my 30v bench supply is not going to help.

I appreciate you taking the time to answer me

[RGB255_0_0]

You can try measuring the AC output of the inverter. From repairing laptops I can say it's not always the CCFL.

[Ohmzilla]

Good call on the CCFL bulbs, o well the bulbs are more than the monitor is worth. They look pretty toasted.

[mariush]

If it's not the capacitors feeding the high voltage circuit powering the cffl tubes...

Either one of the CFFL bulbs is broken or disconnected (sometimes due to heat the wires become loose at the soldering point, or the wire just carbonizes there) , or the CCFL bulbs are using too much current (when they go old they do that) which triggers a protection meant to protect the high voltage transformer and turns off the circuit that produces the voltage for the ccfl bulbs.

ps. yeah, ccfl is dead.

ps. there are on eBay led drivers designed to replace inverters so that you could put led strips where the ccfl bulbs are and connect the on/off and led brightness wires from the display board to the led driver board and maintain the whole functionality... here's such example : http://www.ebay.com/itm/New-15-17-19-19-Wide-22-23-6-24-26-Monitor-LED-Strip-Kit-Drive-Board-/222208441821?var=&hash=item33bca7bddd:m:m0rUGn--ro-_CH5K2hGl7qQ
May want to have a look at something like that, because cffl bulbs are otherwise expensive (and you'd have to buy them in pairs to match the current of each one with the other, otherwise the driver may trigger overcurrent protection) and they can easily be damaged during shipping.