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Accuscore Plus LCD conversion

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  • Accuscore Plus LCD conversion

    Ok, I'm going to resurrect an old topic regarding the conversion of uppers, in my case wells gardener monitors to LCD panels. I started on this a few years ago but it faded into the background as a replacement monitor was found and the urgency dwindled. A recent monitor scare prompted me to actually start prepping for the worst case scenario as storm season approaches. I've read pretty much every thread on here with regards to this subject and a large percentage of source material from arcade and retro conversion websites mainly involving the GBS 8200 converter board. I have read many teething problems getting these boards to work. It seems that the main problem that arises is although these boards can convert CGA from Accuscore+, which we have, but the RGBHV lines breaking out from the monitor control board are running at 15khz. The seemingly logical wiring is to the RGBHV port on the converter, but as most have found out no that matter how many fingers are crossed when powering up its Voila...garbled video output on the LCD and/or failure to lock onto the signal, blank/green screen followed by No Signal and make another cup of coffee and scratch head while hoping staring at it will magically fix it.

    So, after researching over a thousand pages of pre-failed attempts and the results and mods others have done and of course the helpful information Deb and others have contributed here I though my I would share my own revelations and maybe receive a little enlightenment to help fix the most frustratingly "so close but yet so far" final problem I have run into.

    The GBS 8200 I have is V3.0, the CGA input accepts 15khz signal but only through the RGBS port, the RGBHV port will only accept 31khz, rendering the RGBHV harness it is supplied with pretty much useless and only a false hope when wired up.

    So here lies the problem.

    The conversion of RGB and separate H V sync lines into RGBS with combined sync to feed into the GBS 8220 to produce a stable output, something which has proven to be a headache for a lot of people.

    The RGBHV signal from each CWC runs through the house to the monitor control board which lies between each pair of upper monitors. It then is split to left and right lanes via db25 connectors. It is from here that I have taken the RGB signals and wired a harness up accordingly and soldered to the 8220 converters CGA 5 pin connection.
    The separate H V sync lines needed a little jiggery pokery to even get any kind of stable display output.
    After researching sync combiners/strippers/cleaners, only one seems circuit has been able to produce an image.
    I tried twisted sync, stealing the csync from the small amf board the db25 connector plugs into, a basic OR gate, an OR/XOR combination, and a few other coarse methods all to no avail. The only sync combiner circuit that produced a messy but reasonably stabilizable image was using all 4 gates of an SN74LS86 quad 2 input XOR chip with 2 2.2k resistors and 2 22microfarad electrolytic caps.

    I replaced both resistors with variables and set about tweaking them along with the geometry settings and finally have a stable image in the LCD that looks good aside from minor ghosting.

    The one thing that is baking my noodle is when the clamp settings of the board are set to 100 and 99 the colour is perfect but gradually brightens over a period of a few minutes and produces a washed out screen image that can be reset by removing the power and re-applying it, only for the same phenomenon to treat itself. If I change the clamp settings to 81 and 14, there is minimal ghosting, perfectly stable image but the colours are not reproduced correctly, it looks ok but the yellow score grid has a darker yellow hue while the the blue background appears black. No amount of tweaking seems to fix this, it does not increase in brightness to a washed out display like when the colour scheme is correct using different co settings. I actually prefer the colour scheme and actually it's easier to see than the original colours but I'm not one for accepting it in the basis that something isn't quite right and I'm determined to find this gremlin and perfect this.
    I hope someone this information may have been useful to anyone still scratching their head trying to obtain a useable image with a GBS8220 and would be interested to hear if anyone has had the same results or know of a method of correcting what seems to be a clamping/sync related issue.
    Attached Files

  • #2
    Finally the project has come to fruition!

    Success!

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