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Thread: NEC APC III - information needed

  1. #1

    Default NEC APC III - information needed

    Hi All,

    I've got two NEC APC IIIs I'm trying to get up and running. Both of them had faulty power supplies, wouldn't power on at all, but replacing the electrolytic capacitors fixed that.

    Now I get BIOs beeps for the FDD/HDD version, which I assume is normal as I don't have a keyboard or monitor attached. The dual FDD one doesn't beep, but one of it's EEPROMs is corroded so I think I'll try programming a new one, there's a few other patches of corrosion on the motherboard too.

    I'm having a lot of trouble finding information about them online. Anyone know if the keyboard is IBM compatible? What type of graphics do they have? There's both a "B/W" DIN connector and "color" 9 pin dsub. Also, does anyone have information on the dip switch settings?

    I probed the the color dsub for the FDD/HDD one, I got V-freq of 56.4Hz and H-freq 24.8kHz. That doesn't seem to match EGA or CGA, is it some special NEC standard? I'm getting nothing probing the RGB pins with an oscilloscope.

    I think I got the same frequencies on the connector for the dual FDD one, it's all disassembled at the moment so I can't check. What's weird is I get 12V on pin 7 (secondary blue) for this one, 0 Ohm connection to the 12V rail. Is that normal? I assumed the RGB signals would be 5V TTL?
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  2. #2
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    Although it looks, from the outside, like an IBM PC-compatible, it's not. It's a PC98 (NEC Japanese) based system, complete with C-bus expansion cards. Keyboard as well as BIOS, etc. is NEC-peculiar. If you want to see if it boots from floppy, you'll need a PC98 version of MS-DOS (Sometimes called DOS-V). I believe that 2.11 was shipped with the APC III. The floppy drives are Teac 55Fs (or NEC equivalents); 96 tpi DSDD ("720K") There was a "Compatibility" card add-on option that translated some of the interface details to IBM PC, so you could run some IBM PC programs on it.

    Video is 640x400, so closer to the AT&T/Olivetti PCs. You might get an older VGA monitor to crawl down to that horizontal frequency (say a NEC Multisync). Or you could try an EGA monitor.

    If you look for NEC PC9801, you'll find a lot of relevant information on Japanese sites. The NEC version of the PC once commanded 70% of the Japanese market.

    Good luck!
    Last edited by Chuck(G); July 17th, 2020 at 09:28 PM.

  3. #3

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    Thanks, do you think the graphics are also NEC specific? I don't have the original monitors so that might be a problem.

    I do have an EGA/CGA monitor, I've never tested it as working though. I've also have some Epson monitor which works on MDA mode, has a bunch of dip switches on it, I don't think it's a proper multi-scan though.

    I've also got an old monochrome monitor which seems to be composite. The connector is not the same but I think it would be compatible with the B/W connector on the NEC. I saved it from rubbish collection so it needs a new power cable, I might get on to fixing that.
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  4. #4

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    Ops, I think you edited your post while I was writing out my replay.


    Quote Originally Posted by Chuck(G) View Post
    There was a "Compatibility" card add-on option that translated some of the interface details to IBM PC, so you could run some IBM PC programs on it.
    Oh, yeah I have heard a bit about that. But these two don't have it unfortunately. The HDD/FDD one does have ram expansion, sound and RS232 cards.


    Quote Originally Posted by Chuck(G) View Post
    Video is 640x400, so closer to the AT&T/Olivetti PCs. You might get an older VGA monitor to crawl down to that horizontal frequency (say a NEC Multisync). Or you could try an EGA monitor.

    If you look for NEC PC9801, you'll find a lot of relevant information on Japanese sites. The NEC version of the PC once commanded 70% of the Japanese market.
    Thanks that's good to know, I couldn't find the expected screen resolution anywhere. I do have an old working monochrome VGA monitor too, I might give that a go too. The Epson monitor I mentioned does have an AT&T setting, I think I already tried it though.

    Do you know what I should expect on the RGB pins of the NEC color connector if it's working?

  5. #5
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    I'll get back to this when I've had more sleep. I have a III, with said SLE compatibility card. And III specific color monitor. None of it works anymore. I've been tinkering with my scopes so maybe I'll work on getting some of my favo bebes running soon.

    Certain NEC lcd's should work fine. Stay tuned.

  6. #6

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    Quote Originally Posted by tipc View Post
    None of it works anymore.
    Oh, if the power LED doesn't even come on it might be the same power supply issue mine had. Both has the same issue and were completely dead.

  7. Default

    The PC-98 video was based on 2x uPD7220 display controllers. The 24KHz scanrate puts it 'in between' EGA and VGA, but it can also output NTSC composite (mono). Later models of PC-98 had digital and analog RGB, but considering that the APC III is fairly early in the timeline, it probably only has the digital (8 colors). Color itself was optional early on. Without the memory for the extra color planes installed, only one out of three of the color planes was available.

    https://radioc.web.fc2.com/column/pc...ispout2_en.htm

    Nothing there about a DE-9, it might be a different arrangement of the same signals as the DIN-8.

    Without a bootable disk I think it's supposed to boot to ROM BASIC?

  8. #8

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    an EGA monitor will probably sync to that. Won't hurt anything to try in any case, since they use PLLs unlike the old IBM mono displays. 24kHz is the standard "medium res" arcade mode, so a tri-sync arcade monitor would also work, with the appropriate RGB DAC

  9. #9
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    One of the reasons for the popularity of the NEC systems was the higher resolution (400 lines), enabling the clear display of Kanji. The same reason drove the development of high-resolution (21 wire heads) dot-matrix printers. Offhand, I don't recall the Kanji character encoding method--perhaps Shift-JIS; it's been too long since I played with this.

    Another interesting aside is that the µPD7220 display controller, as well as the µPD765 floppy controller was the result of a cross-licensing deal between NEC and Intel (both have Intel part numbers as well; e.g. NEC 765 = Intel 8272).

  10. #10

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    Quote Originally Posted by SpaceDog707 View Post
    I'm getting nothing probing the RGB pins with an oscilloscope.
    you sure about that? you might just be looking at the blanking interval. set your scope for ext trigger on h sync and make sure your time base is long enough for a line of active video

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