Extending the display cables

[colinus]

Hi all, and thnks all for this great forum!
I'm totally new here, and I plan to build a screen tablet from a 15" acer display, and a wacom intuos A4. I already have the components.

For my first question here, I've got a problem.
I have totally dissasembled my LCD panel, and I have made an extension of the display cable (the cable between the display controller unit and the lcd connector).
The original one was approx 15 cm (6") and i have oversized it to 65 cm (25"). I've used the same type of wire (copper, non solid, 0.45 mm2).

The problem is that now I have a lot of interferences in my display, especially if the cable is moving. If I take the cables in one hand, the jitters gently diseapears, but not totally. I've tried to set the refresh rate, the resolution, turned the backlight off, putted an interference filter (ferrite) on my cable, but it's always the same problem.
I've also double-checked my weldings, but it's ok.

Is my cable too long? 

If you have any suggestions, please feel free to reply!
Thanks a lot.

Sorry for my terrible english, it's not my mothertongue... 

[AdrianEvans]

sounds like a loose connection??? did you keep the wound magnet in the long version. I just extended mine and it works just fine...

[AndreZX]

Try shielding the cable. It seems like the extra length means extra interference and is probably shieldable.

Try the aluminum foil and wax paper/plastic wrap method that most of us have resorted to. It might work better than the ferrite filter you tried. Then again, it might not! 

Worth a shot though.

~Andy

[Drewid]

What he said.

[colinus]

Ok folks, I'll made some tests with aluminium foil and wax paper. I post here as soon as I have results.

Thanks a lot! 

[colinus]

Wow!
I've wrapped my cable with:
- two layers of wax paper
- one layers of aluminium foil (the hard one)
- one layer of electrical fabric tape

To this cable I need to add:
- backlight cables (not extended for now)
- usb cable for the wacom

It works perfectly! No more jitters.

Thanks all for your suggestions. Thanks AndreZX for your technique.

Happy happy happy!

I must start a build log  with pics as soon as possible.

colinus

[Switz]

Congrats!
Start a build log asap!

[Monarch]

What type of wire (gauge) did you use to extend the wires that go to the backlight to the inverter? I need to do this myself and wanted to make sure that I purchased the right stuff from the local radio shack.  I am ashamed to say I don't have experience in this type of thing. I know it's a trivial question but I really need to know. I am using the Dell 1503FP AO1 model. I need to go about 15". (yea, it's a long distance but in the end it will make for a clean design build)

Monarch

[colinus]

What type of wire (gauge) did you use to extend the wires that go to the backlight to the inverter? I need to do this myself and wanted to make sure that I purchased the right stuff from the local radio shack.  I am ashamed to say I don't have experience in this type of thing. I know it's a trivial question but I really need to know. I am using the Dell 1503FP AO1 model. I need to go about 15". (yea, it's a long distance but in the end it will make for a clean design build)

Monarch

Hi, Ive not already finished the backlight cables extension, I've just made some tests.
I've used copper cables of two different diameters: 0.75 millimeters square for the positive, and 0.45 for the negative. It works nice, but I have some problems with the insulation system: if I use heatshrin tubes, it dosen't work, my backlight is flashing; if I use electrical fabric tape, it works perfectly. I have to solve this.

I thing you have to use wires with the same diameter than the original ones. My inverter push out 220v at 1.2 A, so I have to use sufficient diameter in order to avoid overheating.

Hope it's useful to you!

colinus

[colinus]

Confirmed:
if I isulate the backlight cables extension with heatshrink tube, I have a flashing backlight. Now I have used electrical fabric tape, and its ok...

could someone explain it?

for tomorrow:
- extending the second backlight cable
- mounting everything on a prototype chassis
- testing with my wacom!

yihaaa!

colinus

[Switz]

Most likely the Heatshrink is blocking the connection somehow.
There isn't really a way to fix it, just try to avoid heatshrink in my opinion.

[id192]

I have had a similar problem with the back light extension as well. I replace it with electrical tape and I have no more flickering problem. An interesting problem indeed

Great tip for any newbie(like myself) having a flashing backlight problem when using the Heatshrink
to insulate the back light cable...  A note of caution when touching those cables as these are  high voltage wire and they are NOT friendly. As I have found out for myself when I was trying to find out the problem of flashing backlight..."YIIKKKEEEs!!!!".."***!!!"... :'( :'( :'( :'(

By the way guys is it necessary to ground the backlight cable when you are shielding it?  

[Drewid]

I'm wondering if heatshrink is prone to slight leakage at high voltages.  I've no idea what it's made of.
Shielding the high voltage cables.  It's not strictly necessariy as far as I know, but if you've shielded everything else and it still jitters then it's worth a try. 

[bernard]

Shielding is not effective if the shield is not grounded.

Yes, the higher the voltage the more it will "arc" (spark to a nearby object) and (probably) disturb more its environment. The pale pink/blue and whit-ish cables are special insulation. Sometimes you can see one of the cable is bigger than the other (one side is more prone to arcing I believe). If you are getting electrical shocks (even minor) when touching it (ouch!) then add extra insulation like electrical tape or heat shrinking tube before shielding it with metal -- else it will arc to your shield!!  Note that air is a good insulation -- so anything non-conductive that will keep an adequate space (like ~1 mm) is good.