Dell Studio One 1909 - 5 seconds to black

[Freezer]

My latest project is a Dell Studio One 1909, it's a 19" all-in-one computer/monitor. The problem is when you turn it on the screen comes up for about 5 seconds and then goes black. If you connect an external monitor the system works fine, so I know the problem isn't the computer side of things. If I shine a flashlight into the screen after it goes black I can still see the image. So the problem is the CCFL backlights.

Taking the back off I first looked at all the caps, especially those on the power supply and inverter boards (less concerned with the caps on the computer motherboard). All caps test fine on my ESR meter. The inverter board is a small board with a 6-pin connector to the motherboard. The pins aren't labeled, but I ran tests and figured each out.

1 and 2 - Both have a solid 12.1 volts during operation.
3 and 4 - Both ground.
5 - When you first turn it on the volts are 0, then after a few seconds it goes up to 3.2 volts and remains steady. I suspect this is the signal from he motherboard to turn on the backlights.
6 - When you first turn it on the volts are 1.6, then after a few seconds it goes up to 3.3 and remains steady. I suspect this is the backlight brightness level.

Since the signals from the motherboard to the inverter look right, I'm pretty sure the problem is either the inverter or the CCFLs. I'm looking for ideas on how to test/diagnose this further. I have two similar sized CCFLs salvaged from another monitor. The connectors are different, but if I adjust the connectors to fit can I just plug those in and try it? I've never swapped CCFLs between monitors before, so I don't know if this will work.

I fear the problem is the CCFLs. When the backlights are on, there is a slight buzzing noise from the monitor.

Attached a picture of the inside of the computer, as well as close-up shots of the inverter.

[diif]

Re: Dell Studio One 1909 - 5 seconds to black

Yes you can adjust the connectors to fit and try the new CCFLs, it can sometimes be just the wiring to the lights and not the tube itself, but this test will eliminate the inverter.

[Agent24]

Re: Dell Studio One 1909 - 5 seconds to black

Try the other lamps to eliminate the inverter, if you need to replace the CCFLs I would get brand new ones, don't put used ones in - who knows how long they will last.

Replacing them is not that hard really, but it's tricky getting the panel apart without damaging it etc so you don't want to have to do it twice.

[Freezer]

Re: Dell Studio One 1909 - 5 seconds to black

I connected some known good CCFLs to the defective monitor. This test allowed me to confirm the inverter board is good. Also, through a process of elimination I can say the problem is the lower CCFL. The upper CCFL works fine.

Now I know where to focus my efforts. When I get a chance I need to remove all the computer parts and get the panel out. This will be my first attempted disassembly of an LCD panel - but I feel up to the challenge. Unfortunately I'm leaving for a long vacation soon, so I'll have to wait 2 weeks or so before starting this project.

The good news is I found this document which details all the steps to removing the computer components.

I'll report back in a few weeks as to my success/failure of this project, along with some more pictures.

[Agent24]

Re: Dell Studio One 1909 - 5 seconds to black

Just make sure you have a clear, flat workspace, and just go slowly and carefully. Take extra attention with the ribbon bonding points at the top\side of the panel etc, make sure you are aware of where they are at all times and don't put any pressure on them etc. It's probably easy to start lifting one end of the panel and forget about the other end, and then find you've torn one of the connections or something.
(Personally, I snapped the CCFL itself the first time I ever did one because I let my guard down after removing the panel and forgot the lamps are just as delicate)

Take notes\photos as you go if you aren't sure about how to get the assembly back together.

Keep the polariser sheets and diffuser etc in the same order, keep them all together if you can, this avoids dust getting trapped between them.

If you are buying new lamps to solder in, buy the lamps first, otherwise you have to work on the panel twice or have it sit around in pieces gathering dust\risk getting broken.

[Chungalin]

Re: Dell Studio One 1909 - 5 seconds to black

Sometimes CCFL are not bad, just the solder failed and caused arcing (ozone smell, important symptom!) on the Cold side (thin wire). I've saved some by just cleaning well burnt zone, removing burnt solder from lamp (difficult, burnt solder gets very hard, it doesn't melt easily!), resolder wire making a ring or loop with cable (this is tricky but important) and put things back together.

Here's a nice tutorial on soldering CCFL: http://www.ccflwarehouse.com/lasotu.html

[Freezer]

Re: Dell Studio One 1909 - 5 seconds to black

I'm back from my trip and I've had a chance to look at this panel. Before disassembling the LCD panel I told myself if the problem was bad solder joints I would try and repair, but if the problem was a bad CCFL tube I would not try and repair it even though you can buy replacement CCFLs. The reason for this is simple. The replacement CCFL plus s/h would run about $20 for a single tube, but on eBay brand new replacement panels cost between $40 and $50 shipped. And the downside to replacing the CCFL is I may spend the $20 to buy the parts for a repair I've never done only to fail and still have to buy the full panel.

Anyway, I started disassembly hoping to find bad solder joints. I was unprepared for how difficult this work is. There are far more parts, pieces, and layers than I was expecting. The biggest problem was trying to get the CCFLs out of the small metal bracket. The CCFLs and wires were both glued and kapton taped in place, and despite my best efforts the metal bracket got bent trying to remove the CCFL. In the end this didn't matter as the problem was a bad CCFL and not the solder joints. The solder joints were fine, but both ends of the CCFL tube were black inside.

As an interesting experiment I tried to reverse the process, reassemble the panel with the bad CCFL, just to see if I would have been able to put it back together if I had decided to buy a new CCFL. I ran into further problems; the various diffusion and polarizing layers would not lay flat and were bunched at the edges, the LCD glass screen was slightly out of position, and the entire panel itself would not close properly - the two metal halves would not press together and snap shut.

My hat's off to anyone with the skill and patience necessary to disassemle, repair, and reassemble an LCD panel.

If anyone is considering this type of repair, on this LCD panel or any one LCD monitor, here's what I would suggest. Find a junk monitor you don't care about (broken or not). Disassemble and reassemble that LCD panel, just so you can see what you're getting into.

My replacement panel should arrive within a week. When it does I'll post additional pictures of the Dell Studio 1909 disassemly and reassembly proceedure. Oh, one more important thing, if you do a similar repair on this make computer/monitor you must have thermal grease on hand. To access the screen you must remove both the CPU and GPU heat sinks which will require fresh thermal grease to reinstall.

As for the broken LCD panel, all is not lost. I'll remove the one working CCFL and wiring harness to use when testing and diagnosing other broken monitors.

[Agent24]

Re: Dell Studio One 1909 - 5 seconds to black

That's a shame you weren't able to get the panel back together. Maybe your panel has a different design to the ones I've done, making it harder to align the layers.

[Jhos]

Re: Dell Studio One 1909 - 5 seconds to black

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