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Flat Screen Monitor went Black

I was on my computer when my Flat Screen Monitor went black. Just suddenly black, no prior indication of a problem. It's a HP 1740.

As far as I know, this monitor has a florescent bulb to light it.

I'm thinking the bulb died, but I'm noticing that the indicator LED is now flashing, not solid "ON". This light is right next to the ON-OFF power switch.

Pushing the ON-OFF switch does not seem to shut it off either. I unplugged it, then plugged it back in and that light just flashes. This makes me think that something else in the circuitry fried. (Just a guess). It would seem to me that if it was just the bulb, everything else would function normally. But I've never worked on one of these monitors, so I dont really know.

I do have electronics knowledge, and used to work on Tv sets and the old CRT monitors, but it's been years.....

So far I have not even been able to get inside this thing. I got the plastic case off, and now there's a metal case, which has screws along the edge, but then there are wires or plastic strips that hold the shell together.

If it just needs a bulb and they are not too costly, I may fix it, but if it's more than that, I'll just trash it. But just for the heck of it, I want to get inside of it. The problem with stuff built like this, is that as the layers come apart, flat ribbon cables need to be unplugged. Even if I can get it apart, how the hell can anyone test them, when stuff is unplugged. Ideally, it could still be plugged in, and I could measure voltages, etc.... That dont seem possible. I suppose like most modern electronics, it's just a throw away item.

This is almost worse than taking apart my laptop computer.

If by chance I can get it open without destroying it in the process, is there a way to test the bulb? Is there a way to test the whole unit without having layers plugged in to those ribbon cables.

It looks to me like this is one of those factory only repairs, where they know exactly how to disassemble it, and have extension cables for those ribbon cables, and special tools to open the case.

It's stuff like this that made me quit repairing electronics. The old stuff was so much easier to work on. Even the old vacuum tube stuff. (I guess I'm showing my age)! :)

Thanks in advance for all help!

Reply to
electron206
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I have a similar ase here only in my case I know the problem is with the LEDS backlighting the unit. Like you I recall burning myself on tubes even before hybrids. I'll just try reflowing some stuff and continuity testing the lighting circuits however your problem seems rather more complicated.

I googled the info to pull mine apart. If I cannot figure it out and fix it in 2 hrs. out to the trash she goes. I've several adaquate units scored from the thrift stores as well as four CRTs

Reply to
Knoppix User

Reply to
John Keiser

Change all the caps. More than once, I've decided that some of the caps have OK ESR. Six months later, taking it apart to change them too.

Also, unplug the thing and leave it unplugged. As the caps resistance goes up, the voltage spike increases. Your voltmeter still reads nominal voltage, cuz that's still the average voltage. Put a scope on it and you see a very different picture. You can get 20V spikes on the 3.3V supply. The Graphics Chips don't like that and will short. Then, you've got a brick.

Reply to
mike

It's probably not the CCFL tubes but rather the capacitors in the inverter section, which is built onto the power supply PCB.

Thank you for including the model number. Please double check the muddle number as it can be a 1740 or an L1740 display. If you're not sure, tear it open and compare the photos in the following links. There are also different mutations of the PCB.

You can buy a recap (capacitor replacement) kit for about $7.00: (L1740) (1740) There are other kits for replacing the semiconductors, which sometimes also blow up. If you don't feel like doing the repair, you can also get PCB's rather cheaply: Again, notice the different PCB mutations.

You will probably find the PCB between the two big xformers to be overheated and scorched. If the PCB crumbles, take some epoxy and rebuild the burnt area. Use your imagination for how to rework the PCB traces. With a single sided board, this should be easy.

Hint: Take some digital photos as you go along so that you can put it back together without extra screws, etc.

Good luck.

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Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
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Reply to
Jeff Liebermann

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