Old Dell 15" - 1 second lights up, then goes black

[tom66]

Re: Old Dell 15" - 1 second lights up, then goes black

What LED strip did you use? I'm looking into doing a LED conversion on a 19", but is a bit unsure on which strips gives enough light. I've found 2-3 candidates, but it's nice to know what's been successful.

Thanks.

I used these:
http://www.giantcod.co.uk/high-densi...-p-404319.html

Perhaps if I were to do it again I would spend a bit more and get these as the display would look at bit brighter. It was originally fairly dim anyway.

http://www.giantcod.co.uk/ultra-brig...-p-406179.html

They are for model aircraft and I used the left over ones from the metre strip (about 30 cm) for my flying wing.

[sofTest]

Re: Old Dell 15" - 1 second lights up, then goes black

What LED strip did you use? I'm looking into doing a LED conversion on a 19", but is a bit unsure on which strips gives enough light. I've found 2-3 candidates, but it's nice to know what's been successful.

Thanks.

[tom66]

Re: Old Dell 15" - 1 second lights up, then goes black

Okay! The conversion is complete!

Assembly is all that remains... How many screws will be missing!? I tried to keep them in one place...

The circuit for the MOSFET on/off is really simple, and is attached.

I used an IRF510 because I had it on hand, if I were properly designing this I would order the right MOSFET. But the current is low enough that the MOSFET does not heat much.

I used a MOSFET because I'm not entirely sure that switch would be happy passing 280mA as at present, it just controls a MOSFET on the main board.

See the video on YouTube: http://www.youtube.com/watch?v=vevU_Fm6ap0

[tom66]

Re: Old Dell 15" - 1 second lights up, then goes black

Good news is it is now working

Turns out it was a loose LVDS cable; it now works perfectly.

Interesting failure mode when powering the LEDs externally and the LCD is powered down. Very weird.

See video.
http://www.youtube.com/watch?v=ETL8q5nq1ro

I'm ordering the resistors and MOSFETs later, will see how it works when finished.

[tom66]

Re: Old Dell 15" - 1 second lights up, then goes black

Good job so far, now for a couple of points.

The signal card is not looking for an 'Inverter OK' signal.

The LEDs will always be on unless you use the 'inverter on' signal to control them.

There is a 4 pin version of the 78XX series of voltage regulators. One example is the Fairchild KA278RA05CTU. The additional pin is an enable / disable control. You can use that to drop the voltage and turn the LEDs on and off. A REALLY clever guy could even figure out how to use the brightness control to adjust the brightness (don't look at me).

PlainBill

I wouldn't use a 78 series regulator because it's far cheaper to use a power resistor. Also, a 78XX wouldn't drop current, so thermal runaway is a real possibility - not pretty! If I were hyped up about efficiency, I'd use one of my buck converter LED drivers I designed, but I don't have the time at present.

For on/off, I figure I will just wire in the gate of the FET to the 18V_ON on the control panel. This comes out of the switch only when the monitor is on and could probably drive the FET into conduction.

Problem is, at the moment, the display is still white - no video signal is being sent to it. I cannot get the signal board to power up. I tried shorting various connections on the inverter board to turn it on with no luck.

How would the signal board know to shut down with a bad inverter/CCFLs, as was the case before?

[PlainBill]

Re: Old Dell 15" - 1 second lights up, then goes black

Well the good news is, the LED strip I bought for £5 is really bright, and it looks like I can meet the original brightness of the CCFL. I burnt out some LEDs rather stupidly on one strip but it doesn't seem to have significantly affected it.

I'll need to drop 18V down to 12V at about 250mA, this means according to V=IR, I need a 24 ohm resistor, so I'll order a 27 ohm 3W resistor (the resistor will dissipate 1.7W, so I will attach it to the metal casing to help dissipate some of the heat.) I'll probably wire in a MOSFET to control the brightness too.

I need to figure out how to get the monitor to turn on without the inverter; it might be waiting for an "Inverter is okay" signal.

Now I know why to be annoyed when manufacturers want an extra £100 for an LED vs CCFL TV .

It's also interesting that this LED array only consumes around 4-5W but has almost the same brightness as 10-20W CCFLs. More efficient technology I guess.

Good job so far, now for a couple of points.

The signal card is not looking for an 'Inverter OK' signal.

The LEDs will always be on unless you use the 'inverter on' signal to control them.

There is a 4 pin version of the 78XX series of voltage regulators. One example is the Fairchild KA278RA05CTU. The additional pin is an enable / disable control. You can use that to drop the voltage and turn the LEDs on and off. A REALLY clever guy could even figure out how to use the brightness control to adjust the brightness (don't look at me).

PlainBill

[tom66]

Re: Old Dell 15" - 1 second lights up, then goes black

Well the good news is, the LED strip I bought for £5 is really bright, and it looks like I can meet the original brightness of the CCFL. I burnt out some LEDs rather stupidly on one strip but it doesn't seem to have significantly affected it.

I'll need to drop 18V down to 12V at about 250mA, this means according to V=IR, I need a 24 ohm resistor, so I'll order a 27 ohm 3W resistor (the resistor will dissipate 1.7W, so I will attach it to the metal casing to help dissipate some of the heat.) I'll probably wire in a MOSFET to control the brightness too.

I need to figure out how to get the monitor to turn on without the inverter; it might be waiting for an "Inverter is okay" signal.

Now I know why to be annoyed when manufacturers want an extra £100 for an LED vs CCFL TV .

It's also interesting that this LED array only consumes around 4-5W but has almost the same brightness as 10-20W CCFLs. More efficient technology I guess.

[tom66]

Re: Old Dell 15" - 1 second lights up, then goes black

The original CCFL is about 310 mm long. I checked a spec sheet, and the rated brightness is 46,000 Cd/m^2

PlainBill

I was going to use 1206 SMD LEDs rated at 260mcd each. The tube is about 2mm dia and 310mm long = that means 2 * pi * r * h = 0.004m^2 = 223 cd for the tube. That means I'll need 1,000 LEDs+, which seems like way too much given that I've seen Edge LED screens with far less.

[PlainBill]

Re: Old Dell 15" - 1 second lights up, then goes black

As an idea on how to size my LED strip, can anyone give me a source for the average light output from a single CCFL in a 15" monitor at full brightness?

The original CCFL is about 310 mm long. I checked a spec sheet, and the rated brightness is 46,000 Cd/m^2

PlainBill

[tom66]

Re: Old Dell 15" - 1 second lights up, then goes black

As an idea on how to size my LED strip, can anyone give me a source for the average light output from a single CCFL in a 15" monitor at full brightness?

[tom66]

Re: Old Dell 15" - 1 second lights up, then goes black

I'm almost tempted to do an LED conversion as the CCFLs are $10 each and the inverter is $14. Not really worth it. I can buy two strips of high power white LEDs (total around £9) and run them straight off the 18V supply (possibly using a relay or FET to switch them on, so they don't run when the monitor is in standby.) To be considered, I'll let everyone know how it goes .

[PlainBill]

Re: Old Dell 15" - 1 second lights up, then goes black

Hmm, I tried to push the lead back in, but I got a sound like glass being crunched. Sounds almost like the tube is broken or was broken by me putting the lead back in. I guess, since the tube is broken, I will need to dispose of it properly; is there a way to remove it from the support it sits in and change it out for a new one?

Yes. The best way is 'carefully'. I'd suggest spending some time on the CCFLwarehouse site, looking at all the information they have on supplies and procedures. I've never reached that point. I have heard that one way is to simply remove the old tube and the silicone mounting blocks, solder the leads to the new CCFL, then use silicone adhesive to hold the tube in the channel.

PlainBill

[tom66]

Re: Old Dell 15" - 1 second lights up, then goes black

Yeah, a loose high voltage lead would explain everything. You were lucky; every one I had to deal with required a complete disassembly of the LCD panel.

Several users have reported excellent results with CCFL Warehouse.

As far as replacing the inverter, it's your call. I guess what I would do is repair the broken lead and seal any damage with silicone adhesive, letting it cure for a day or so. Then test both CCFLs on the existing inverter. Using the swap technique you can determine if there is any problem with the existing CCFLs and inverter. If everything works, put it back together and cross one more item off your bucket list. If there is any problem, I'd replace both CCFLs and the inverter.

PlainBill

Hmm, I tried to push the lead back in, but I got a sound like glass being crunched. Sounds almost like the tube is broken or was broken by me putting the lead back in. I guess, since the tube is broken, I will need to dispose of it properly; is there a way to remove it from the support it sits in and change it out for a new one?

[PlainBill]

Re: Old Dell 15" - 1 second lights up, then goes black

Okay, they weren't too difficult to remove once I figured out how to do it. They are on little sliding rails and come out in these modules.

So, when I was removing one of them, the pink wire on one of them came loose very easily. Could this have been causing the problem?

What source for CCFLs would you recommend?

Do you think a new inverter would be a good idea too?

BTW, the LCD panel part number is LM151X2 and it is made by LG-Philips LCD (Korea).

Yeah, a loose high voltage lead would explain everything. You were lucky; every one I had to deal with required a complete disassembly of the LCD panel.

Several users have reported excellent results with CCFL Warehouse.

As far as replacing the inverter, it's your call. I guess what I would do is repair the broken lead and seal any damage with silicone adhesive, letting it cure for a day or so. Then test both CCFLs on the existing inverter. Using the swap technique you can determine if there is any problem with the existing CCFLs and inverter. If everything works, put it back together and cross one more item off your bucket list. If there is any problem, I'd replace both CCFLs and the inverter.

PlainBill

[tom66]

Re: Old Dell 15" - 1 second lights up, then goes black

Okay, they weren't too difficult to remove once I figured out how to do it. They are on little sliding rails and come out in these modules.

So, when I was removing one of them, the pink wire on one of them came loose very easily. Could this have been causing the problem?

What source for CCFLs would you recommend?

Do you think a new inverter would be a good idea too?

BTW, the LCD panel part number is LM151X2 and it is made by LG-Philips LCD (Korea).

[PlainBill]

Re: Old Dell 15" - 1 second lights up, then goes black

As a learning experience, I will try to repair this. So what would be the next steps.

I already have two 14" LCDs (just found the other one in the roof), and an 18". This one would just be a trophy for me.

A trophy monitor? Well, it's less expensive than a trophy wife.

Disassemble the LCD panel until you reach the CCFLs. This has been a royal PITA every time I have had to do it. Look for signs of damaged wires, arcing, or broken CCFLs. Try not to get any dust into the layers.

PlaiinBill

[tom66]

Re: Old Dell 15" - 1 second lights up, then goes black

At a minimum you have a broken CCFL or wire (probably the high voltage wire). This may have damaged something in the bottom section of the inverter.

If I had the monitor on my bench at this point I would be saving the CCFLs and the power adapter. The rest would go to a recycling center. A working 15" LCD monitor goes for anywhere from 'Name your price' to $30 locally. I don't think many get sold at $30 or $25.

PlainBill

As a learning experience, I will try to repair this. So what would be the next steps.

I already have two 14" LCDs (just found the other one in the roof), and an 18". This one would just be a trophy for me.

[PlainBill]

Re: Old Dell 15" - 1 second lights up, then goes black

The power indicator light stays on and the supply voltage stays at 17.87V when it switches off...

Without inverter, the display is visible, if you look carefully.



Both plugged in: 2secs to black
Bottom not plugged in: 2secs to black
Top not plugged in: nothing

I then flipped the inverter board around. Top output -> Bottom CCFL. Bottom output -> Top CCFL. The result was a small, brief buzzing sound (<200ms) from the inverter and nothing else - no light.

Then I connected just the bottom CCFL to the top output. Result: VISIBLE ARCING on the PCB pins of the transformer and on the component side of the board as well as a loud buzzing/clicking sound (like a cricket.)

Then I connected the top CCFL to the bottom output. Result: nothing. No light.

Any idea?

At a minimum you have a broken CCFL or wire (probably the high voltage wire). This may have damaged something in the bottom section of the inverter.

If I had the monitor on my bench at this point I would be saving the CCFLs and the power adapter. The rest would go to a recycling center. A working 15" LCD monitor goes for anywhere from 'Name your price' to $30 locally. I don't think many get sold at $30 or $25.

PlainBill

[tom66]

Re: Old Dell 15" - 1 second lights up, then goes black

Were missing something, with the inverter fuse bridged the whole monitor is shutting down [loosing the very dim display] There is something shorted in the inverter section.
I would suggest powering on the monitor without the inverter plugged in, see if you can see the dim display

The power indicator light stays on and the supply voltage stays at 17.87V when it switches off...

Without inverter, the display is visible, if you look carefully.

The pictures of the inverter confirm it. It's our old friend the Royer oscillator. The transformers are driven independently, but controlled from a single controller. If either CCFL or inverter section is bad, you will get 'two seconds to black'.

Earlier you did a test where you tried using only one CCFL at a time; the top one lit, the bottom one didn't. Let's describe it this way. You have two plugs on cables going to top and bottom CCFLs. You have two sockets for top and bottom plugs. They are the outputs of the top and bottom inverter sections.

Connect top plug to bottom socket and test. If the CCFL comes on, the bottom inverter section is good. The problem is the bottom CCFL or the CCFL wiring. If BOTH CCFLs will light on the top socket, but neither will light on the bottom socket, the bottom inverter section is bad. If the top CCFL will light on either socket, but the bottom CCFL won't light on either, the bottom CCFL (or it's wiring) is bad.

PlainBill

Both plugged in: 2secs to black
Bottom not plugged in: 2secs to black
Top not plugged in: nothing

I then flipped the inverter board around. Top output -> Bottom CCFL. Bottom output -> Top CCFL. The result was a small, brief buzzing sound (<200ms) from the inverter and nothing else - no light.

Then I connected just the bottom CCFL to the top output. Result: VISIBLE ARCING on the PCB pins of the transformer and on the component side of the board as well as a loud buzzing/clicking sound (like a cricket.)

Then I connected the top CCFL to the bottom output. Result: nothing. No light.

Any idea?

[alexanna]

Re: Old Dell 15" - 1 second lights up, then goes black

The inverter shutting down also turns off the LCD display. (Before, with the blown fuse, you could at least faintly see the display.)

Top only: switches off in <1 second
Bottom only: nothing (never comes on)

Any idea what the problem might be?

Thanks,
Tom

Were missing something, with the inverter fuse bridged the whole monitor is shutting down [loosing the very dim display] There is something shorted in the inverter section.
I would suggest powering on the monitor without the inverter plugged in, see if you can see the dim display