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need solution display monitor adapter ANALOG RGB to VGA ..

Discussion in 'NEC PC-88 and PC-98+ PC-FXGA' started by nabilafauztin, Feb 21, 2015.

  1. nabilafauztin

    nabilafauztin Newly Registered

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  2. Lum

    Lum Officer at Arms

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    Hmm I really don't know much, but depending on the monitor you may need some kind of video converter.
    Older PC 98 models were of course created before VGA.
     
    Last edited: Feb 24, 2015
  3. Venatus Usque

    Venatus Usque Site Supporter 2014, 2015

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    I would recommend using the GBS-8200 CGA/EGA/YUV to VGA converter/upscaler (USER MANUAL ). I have two; one on my Supergun and the other on a SCART to VGA upscaler that I built … converting RGB to VGA output.

    There are many videos of this converter (GBS-8200) on YouTube using RGB to VGA.

    Here’s an example of an Amiga A2000 using this converter. This Amiga has an RGB 32 pin, two-line output: Amiga A2000 using RGB to VGA converter 15khz to 37khz (first 30 seconds of video)

    Here’s a pin-out chart for the PC 98; Japanese RGB-15 Connector.
     
    Last edited by a moderator: Jul 12, 2015
  4. MrF

    MrF Member

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    I joined up to research this, I have a pc9801uv, and I have been loaned a monitor which can work with its low sync rate (think it is 15khz) and I am using a vga plug cable which came with my PC98, but I have to give this monitor back to the owner now I know the machine works. I bought a GBS-8200 clone on ebay to use with this and a vga monitor, but it cannot see any signal on its inputs when I plug the NEC vga style cable into it. The vga pins are on the same traces as the header cable in use in the amiga video linked above, I know my pc98 has graphics output, and I know my cable with a vga pin on is good because it works for the monitor too. Does anyone know if this does actually work for this? I can reuse this gbs on my amiga 2000 like in the video, but I still need to find a way to connect the 9801 to a normal vga monitor.

    I read the manual linked above again, and it says only the pins for the cga plug support 15hz input. So tomorrow I will make a cable up to use those pins instead of the D plug input and see if that is the problem, and report back if it suceeds.

    And to update, I read the manual again and misread it yesterday, the vga covers ega/cga inputs too. But it does not work for me. I can see little flashes of the display output and if I start the config up at he right time I can see the screen in the background of the menu but all mixed up, but once I exit the menu the GBS decides there is no signal to sync to and cuts the display. Perhaps a sync issue, or just a junk gbs clone. It would be good to know if someone has used one of these on a pc9801.
     
    Last edited by a moderator: Apr 1, 2015
  5. Bad_Ad84

    Bad_Ad84 Keyboard Error: Press F1 to Continue

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    did you hold down the auto button?

    also tried changing the mode?
     
  6. MrF

    MrF Member

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    Yes, in auto mode if I switch off the pc98, the GBS board shows the no signal screen, then when I switch on the pc98, it tries to sync to the signal, but fails then goes back to the no signal output. If I switch mode manually, it shows the mess as it tries to sync, but doesnt lock up. It could be bad wiring still missing one of the sync signals or too low a level for the GBS board. I have tried maybe 9 monitors, crt and lcd, and only this single lcd monitor out of a server cabinet works so far, I think because it was made to support very low scan rates on console displays of old servers. But I need to return it. I have another pc98 and it is the same issue with that too, but that has a problem with the output because even on the good monitor the display only has the green component working. I think I have a jamma monitor cable I can rewire in case the board does need to use that socket instead of the D connector, or maybe the D sync signals are in the wrong pins. Ill try that next.

    No, its the same with a wire or using the pc98->vga cable I already have. I put a meter on the cable I have and it maps the pc98 16 pin DIN to the vga pinout on the other end. And then I made an adaptor for pc98->GBS jamma connector pin header. Why is there a dot clock and +5v coming out of the pc98 socket? I know with the floppy diskettes they moved some timing circuitry into the floppy drive itself, which is why the need for extra circuits in the floppy emulators for them to work. Maybe there is something odd about the display output too. But I cant explain why the first monitor just works. The other monitors display a timing out of range error (do not support low enough scan rates) but the GBS cannot even see a signal. Ill take this GBS for my Amiga and carry on searching for a better pc98 solution. Yahoo auctions again perhaps.
     
    Last edited by a moderator: Apr 1, 2015
  7. Venatus Usque

    Venatus Usque Site Supporter 2014, 2015

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    The link for the Amiga; was to show that it's possible to connect a VGA monitor using the GBS-8200.
    The Amiga and the PC9801 have different video pin outs. My post above provides a link for the PC98 ... did you use that chart to match up the connections on the header connector of the GBS-8200?

    Make sure the power supply is outputting a minimum of 2amps, the GBS-8200 will not function properly.
     
    Last edited: Apr 1, 2015
  8. retro

    retro Administrator Staff Member

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    Good to have you here - welcome to the forums! However, please calm down a bit....

    Firstly, your post was moderated by the anti-spam system, as explained here. You would have also received a message telling you it was awaiting moderation. If you don't see your post immediately, be patient - a moderator will get around to approving it. There's no need to keep posting the same thing over and over again until it appears.

    Also, please don't double/triple post. If nobody has replied within the past week (and certainly not within minutes), use the edit button. You can also use the quote button to make it easier to see what post you're replying to, or the multi-quote button to quote several posts at once.

    Anyway, enjoy the forum!
     
    Last edited: Apr 1, 2015
  9. MrF

    MrF Member

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    Understood, it proves the idea works not the exact step by step instructions for the pc9801. The psu is 10amp. I think now either this specific GBS clone I have is junk, or the pc98 needs something else also (timing signal from the monitor?). I will test the GBS on my Amiga, and find another monitor for the PC9801. A internet friend is sending me some model numbers of known pc98 working monitors to search for.
     
    Last edited: Apr 2, 2015
  10. MrF

    MrF Member

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    Update as promised. GBS9800 worked on amiga, but still cannot get it to function on pc98. Has anyone actually got a GBS board working on a PC9801?
    For me, someone has given me a old 15khz capable rgb monitor that can display amiga etc natively, so I will wire it to this to see. I know the PC9801 has display output because it worked on that one special monitor.
    Looking at plug spec, does the pc9801 need a clock signal from monitor or other strangeness? The same thing happened on the floppy drive interface.
     
  11. Venatus Usque

    Venatus Usque Site Supporter 2014, 2015

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    I did a some additional research on this; it appears that the PC-98 displays video at 24khz.

    Looking at the GBS-8200 manual; RGB input is recognized at the 30.5khz – 32.5khz range, therefore, the GBS-8200 will not sync the computer and monitor.

    I should of looked at this a little closer when I replied to the OP, but made the assumption that if it worked on the Amiga… it could work on the PC-98… Sorry, I feel bad about all the time you spent on this.

    Reading back through your posts, you made mention that you had an NEC VGA cable; in order to use a VGA monitor, it will require that it support 24khz frequency.

    An alternative solution; but rather expensive, is this video scan converter: XPC-4, it specifically notes support for the PC-9801.

    These are available online from various merchants including eBay and Amazon.
     
  12. dj898

    dj898 Site Supporter 2015

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    PC-9801? Boy that brings memory. ^ ^
    I once had Analog RGB monitor that used with PC-9801 as well as FM-NEW7 back in late 80s.
    It's heavy 14" monitor from memory. Those were obviously designed for 15Hz signal.
    Think there was SONY LCD TV/monitor that can sync at 15Hz signal as well - late 90s?
    If you can get hold of one try to see if it works.
     
  13. MrF

    MrF Member

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    I ended up not returning the special compaq rack monitor, instead my friend now owns my spare cd32 console he was lusting after and is happy too :)
    I traced the offical nec vga cable out with a meter and it is just a straight cable with pins connected as per the wiring guides, no extra pins or resistances inside.
    But, I got a second pc98 and connected it to a belkin omni kvm and now I can run my normal 19" generic vga monitor on the second one in the office too. I know the belkin interfers with scan rates because I can run higher resolutions without it in-line on my main pc, so maybe its acting as some kind of converter for the video scan frequencies.
     
  14. Melchior

    Melchior Rapidly Rising Member

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    The GBS Is picky about certain refresh frequencies; e.g. Arcade style ones its very twitchy with (e.g. anything not 15Khz or 31Khz - 30/29/24Khz and other non-standards).

    That said there are 3 or 4 different versions of the GBS82XX available - some do kinda work with additional signal clean-up. (e.g. sync regenerators)
     
  15. MrTimscampi

    MrTimscampi Member

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    If I remember correctly, the PC-9801 uses 24Khz video at 640x400. (There's also a mode in 640x200 at 15Khz)
    More recent models (Mid-90s) had VGA support and output 31Khz, but were made primarily for Windows.

    Micomsoft makes an (expensive) converter called Micomsoft XPC-4. It's made specifically for the PC-98, X68000, FM Towns, ...
    But it's 40,000¥.

    I ended up importing a NEC PC-KD854 from Japan, for about 150€. If you hunt a bit on Yahoo Auction, screens like that can be found rather easily and cheaply.
     

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