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Problems with screen backlight and allen controller setup

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  • Problems with screen backlight and allen controller setup

    I tested my screen (lg lca4ve02a) about an hour ago, but i ran into a few problems:

    1) The screen doesn`t light up. I put a voltmeter across the output of the inverter, and got 60mV at 50hz. This seems like a very low voltage, and the brightness control makes no difference to this voltage. I`m using an ac at psu to test the supply, and this reading stays the same whether the PSU is on or off, so i suspect i have a bad inverter. If anyone could confirm that i`m correct, plz reply. The inverter came with the screen (damn ebay), and it`s called Unidim, and is made by Computer Dynamics.

    2)I then used a torch to see the pixels of the screen. The screen is connected to an allen controller with a homemade hirose cable, which i checked for shorts, etc. When i looked at the screen, there are blocks of white and blue, and the blue blocks have turquoise stripes across them. The screen also takes about 2 seconds to refresh, it`s looks like a jpeg loading on a really slow computer. I havent a clue what is going on here, this problem seems a lot harder to solve than the 1st problem. Is the screen bad, or is the controller the problem. I`m using 640x480 @ 60hz, and i`ve tried double checking everything, but 2 no avail. Plz help, i need to get this lot in the car soon! Thanx in advance.
    My Setup

  • #2
    Ok, i had another go at it today. The backlight inverter was definately the problem, cause i tried another inverter, and the screen now lights up fine.

    However, i`m still stuck on the problem number 2 (see previous post). I`ve tried different video cards, different computers, but the screen, controller or the connections are definately at the heart of the problem. If anyone has had a similar problem, or know of anything else i could try to get this going.... plz let me know.
    My Setup


    • #3
      Mine makes those patterns when it loses it's signal. When I put it in standby, it'll flash that for a sec before it goes to black. I think it's your cable. :/

      Oh, and your avatar scares me


      • #4
        Thanx for the info. I'll check my VGA input cable.... (I have wired in seperate grounds in for the red, green and blue signals, but i have no gounds on the hsych and vsych signals... is this right?). The wierd thing is that the white and blue pattern changes when the computers signal changes... as it boots up (the computer is showing the win98 bootscreen), the screen was loads of white, but when the computer has booted, the lcd shows a lot more blue, so the signal is sort of getting there somehow.

        Oh, and don`t worry about my avatar, the face isn`t mine. It`s actually Aphex Twin, who does really wierd electronic music. I can change it if you like.
        My Setup


        • #5
          You probably don't have the hsync or vsync right. Maybe you have them switched or something. Also, pins 5 and 10 on the VGA need to go to the same ground the controller is connected to.


          • #6
            Thanx again 4 the help... I just checked every single pin on my vga/power lead, and everything is at it should be (no shorts, etc.)... heres how i've got it wired:

            controller plug - vga plug
            pin 1 ----------- pin 5,pin 10 and power ground
            pin 2 ----------- power 12v
            pin 7 ----------- pin 8
            pin 8 ----------- pin 3
            pin 9 ----------- pin 7
            pin 10 ---------- pin 2
            pin 11 ---------- pin 6
            pin 12 ---------- pin 1
            pin 14 ---------- pin 14
            pin 16 ---------- pin 13

            Yet it still doesn`t work. This is right isn`t it?
            My Setup


            • #7
              That is correct.

              Time to painstakingly check every connection on both the vga cable and your hirose cable


              • #8
                After spending ages checking the vga lead, i found the hirose lead was the problem. Virtually all the connection are in the wrong order, so i`ve now got to spend ages resolding, and getting the order correct. I hope this lot still works when i plug it up properly. Well, at least I found the problem. Thanx again 4 all your help... It`s much appreciated.
                My Setup


                • #9
                  The saga continues:
                  Ok, I spent ages resoldering my hirose lead. I checked it twice, and it is definately correct (connected one to one). I was expecting it to work, so I tested the whole setup again about 2 minutes ago: all i got was a blue screen with a few static stripes for the first second the computer was on. All i got then was a black screen. That`s it. I let the computer boot, still nothing. I checked brightness, etc. but still nothing. So... I have absolutley no clue what the problem is. The only possibility i could think of is that i must have damaged/killed something when i used the incorrectly wired hirose lead. Anyone, plz. help!
                  My Setup


                  • #10
                    Ok, the 5v regulator on the allen controller is fine, I tested it today, but I`m now totally stuck as the spare inverter I was using had to be returned (i borrowed it from a laptop). Anyway, the inverter that I got with the screen (a Computer Dynamics Unidim revision A.02 - datasheet here ) isn`t dead. It outputs zero volts to the screens backlight, and here is why:

                    The inverter consists of a base board, with all of the connectors and circuitry to do with brightness control. The base board also has a daughterboard piggybacked on it, which does the actual inverting. The daughterboard was 2 inputs from the mainboard... v+ and gnd. The problem is that 12v from the power connector goes straight to the v+ connection on the daughterboard. The ground is meant to have a variable voltage to control the screens brightness, but the never reaches the gnd of the daughterboard, so no high AC voltage is produced (open circuit). I did "cheat" though... I wired +5v and GND from a AT psu straight to the daughterboard. This gave an output voltage of 340V AC (rms i think), but this wasn`t enough to power the screens backlight up, however.

                    So i have three options here:
                    1) Make my own variable PSU that outputs between 5volts and 12volts (tricky).
                    2) Replace the components on the mainboard, and hope the mainboard works and gives the correct voltages to the daughterboard.
                    3) But a new inverter (no money tho).

                    Any help appreciated.... I feel like everything's stacked against me here.
                    My Setup


                    • #11
                      Yeah this is offtopic but after MP3KID and now MikeHunt I think we have to make a new rule --- NO SCARY AVATARS!!!!


                      • #12
                        Ok, your not the first one to comment, so I changed my avatar to something less scary

                        Oh, and to get back on topic.... I finally got the damn thing going, here's how i did it:
                        1) I put 12v straight to the inverters daughterboard. The screen now lights up. No brightness control though.... but i'll sort it.
                        2) Thanx to infrared 4 this one: I rewired +5v to the LCD through the hirose lead, as I blown the contollers onboard PSU with my crappy wiring.

                        Anyway, the damn thing now works... I am so happy! I now have a fully functioning 10.4" LCD with 18 bit colour! I just have to make a housing now...
                        My Setup


                        • #13
                          Yay! glad everything works for you

                          btw, if that's a guy's face, your new avatar is equally scary


                          • #14
                            Thanx again arby, i`m still can`t believe i got it going (woohoo).

                            About my avatar... Judge 4 yourself! I`m gonna change it to a piccy of my car when i get my digicam back, which should be in about a week or so.
                            My Setup