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Thread: Gridcase Laptop EL Display Help Requested

  1. #1

    Default Gridcase Laptop EL Display Help Requested

    Hello all.
    My name is Shawn. I will apologize in advance. This post may get long and involved.
    I am the owner of a TEMPESTed Grid Gridcase (8086) that originally had a broken EL display. The display was visibly cracked and could not repaired. The display is a rare Sanyo LJ640U07. I thought I could get lucky and hack in a newer Sanyo LJ640U34. That ended disastrously in a $450 failure.
    My next goal was to verify that the video circuit was still alive. The goal was to connect an external monitor to the Grid and get a display. The laptop boots form the floppy. I can type 'dir' and see drive activity. So, I know the computer is alive.
    I want to connect an external monitor and see a command prompt. I have been unsuccessful.
    I attached a picture of the motherboard. The 15 pin female connector is the video connector. Of course, it's not a standard pin configuration.
    I have an Digilent USB Analog Discovery 2 module that I use as an 'scope. The pins of interest are pins 1 - 5. There are display supply voltages on 6-8, and mostly grounds on 9-15.
    One interesting fact is pin 5 is not connected to anything inside the mating connector. Of course, the display is a monochrome display. So, wouldn't only 1 be needed? If two are being used, is it red and blue? Blue and green? Green and red?
    Looking at online documentation, an analog display basically needs H-Sync, V-Sync, Red, Green, and Blue.
    Using pins and alligator clips, I've manually connected the Grid video lines to a variety of newer LCD displays and older CRT displays. Other than make them "come alive" for a few seconds, I cannot get anything to appear on the display.
    I will attach screen shots of the waveforms on the different pins. The waveforms look OK to me, but I can't get a monitor to recognize them.
    Perhaps someone will say, "Oh, the waveforms look great. Just plug in a <insert magical device> and it will work just fine!" HA!
    I am thinking of "throwing in" some sort of 6 inch tablet display. Worse case, run an cable outside of the laptop and connect it to a standard monitor.
    If the people of the forum could give me some pointers, or tell me what I'm doing wrong, or what I need to to, I would appreciate it. Any (reasonable) suggestion would be appreciated.
    Thank you,
    Attached Images Attached Images

  2. #2
    Join Date
    Jan 2018
    Los Angeles, CA, United States


    Hi Shawn, I believe we recently corresponded on the grid yahoo board about TEMPEST motherboards (but, for some reason my name shows up as a bunch of numbers/letters there).

    Coincidentally, I actually ran into this same issue last year and spent quite a bit of time trying to get something out of that odd video connector.

    First of all, I believe you might be talking about a Sharp LJ640U07 EL Display. I only bring that up because there are datasheets floating around for the "cousins" to the LJ640U07 which provide a bit of info on what is the display expects to receive (I realize you might have mis-typed, since you reference purchasing a LJ640U34, which is one of those "cousins" I was referring to).

    I was able to use the input signals table from several Sharp models of that vintage (including the LJ640U34), to determine which signals were common to all models. I do not have my findings in front of me at the moment (in a notebook somewhere), but off the top of my head: I believe that there's a vertical sync, horizontal sync, a data line, and a clock. There might have been more, but that's what I seem to remember. Also, there were multiple power lines since the display required both +5v and +12v (actually, it might have even been higher than 12v?)

    I'll look for my notebook and get back to you with which pin is which, or at least what my best guess was at the time.

    In any case, the short version: The video signal is, I believe, a form of TTL video. I was able to get a picture up on a Commodore monitor (will attach a picture here) by hand-wiring a DIN-8 plug to the monitor's "RGB TTL" port. The picture was distorted, but readable. In later attempts, I believe I was able to clean up the picture and fix some of the skew/shear/etc. by shielding the connections (but, I might have just jostled something and got it working, to be honest).

    There's hope!


  3. #3
    Join Date
    Jan 2018
    Los Angeles, CA, United States


    Alright, I found some of my notes on that video connector.

    What I'd done to try and reverse-engineer what was going on was:

    I pulled apart the AMP connector shell, (attached to the EL Display assembly), and traced the wires coming from the display to their corresponding pins on the board. I then traced around the board to find the first stop for each of these. And lastly did some scope'ing around to see what was on each one.

    Pin 1: (Brown wire in AMP connector)
    Connects to -> C31 -> U41 7474 flip-flop's 2Q (Pin 9)

    Pin 2: (Red wire in AMP connector)
    -> U41 7474 flip-flop's 2CLK (Pin 11)

    Pin 3: (Green wire in Amp Connector)
    I believe this is horizontal sync
    -> U62 (Pin 9) 7474 flip-flop's 2Q (Pin 9)

    Pin 4: (Blue wire in AMP Connector)
    I believe this is vertical sync at 60Hz
    -> U78 7404 (Pin 5)

    Pin 14: (White wire in AMP Connector)
    I don't know what this does, but there's a note that says "Possible Data?"

    Depending on the board revision, I realize the connections might be completely different, but I'm guessing the overall situation is rather similar since the EL Display itself is the same model.


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