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sanyo mbc...

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    sanyo mbc...

    ...25 Plus. it was a kind of teaser
    don't look for it on google, you'll find nothing at all. this is what we can call a kind of "rare" machine.

    so, it's a "semi AT" clone, as it's a 286 @ 12,5 Mhz, but with only 8-bit isa slot. but got an onboard ide xt interface, and vga. it's really a compromise machine...
    i had the chance to get it with original manuals, dos floppy, keyboard, and it's box. and it's a nice looking little pc, from my personal taste.

    but of course, i got an issue with it. it doesn't want to see any extended ram.
    this machine use a mix of zip chip and 2 regular 30 pin socket, for acheving 4MB.
    so, i got a set of zip chip... first try was wrong, i used 256kbit x4, and he doesn't support them, so got 1mbit x1 and this time, it's ok.
    the onboard 1MB are 256x4 zip chip, by the way... that's why i tried that first.

    when you add extended ram, the onboard ram is disabled.
    so, at boot it scan for the 640 + 384 reserved ram, till here, it's ok... he see the external chips and use them for the base ram, but he didn't scan beyond 640KB...
    what can be wrong in this case ? it's a bit like if the bios don't have the ability to go beyond.

    i checked the zip and simm pinout, to see if it's ok, and it is.
    the pcb silkscreen give the simm and zip references : MB85230 for simm module, which use standard pinout, and 811000 for the zip.
    811000 give nothing on google, but i guess it's 81C1000, and you find the schematics for them. and they are standard pinout zip.

    all is configured by switches, all is set according to the manual.
    so, for the moment, i give up. i don't understand what happen here. if you have some ideas...
    thanks
    Last edited by whaka; May 5, 2021, 04:33 AM.

    #2
    To access more than 1024kb the 286 must be switched to protected mode. Maybe that system do not support that. This wan't uncommon, most systems used 286s only for the extra speed but aren't real AT clones.

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      #3
      why mounting extra slots/socket for ram extension ? and best of all, why the manual give the procedure for upgrading to 2 or 4MB ?
      this is a total nonsense if it's really the case.

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        #4
        Originally posted by dieymir View Post
        To access more than 1024kb the 286 must be switched to protected mode.
        That's nonsense. Even with a 8088/XT you can use more than 1024 kb of RAM. Protected mode only changes how you access the RAM. Protected mode is needed for XMS, not for EMS.

        Anyway, what chipset does that SBC use? You may only see the extra memory by loading an EMS driver under DOS.
        Last edited by Timo W.; May 5, 2021, 07:06 AM.

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          #5
          if i identified it correctly, it's a chips F82C230

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            #6

            hmmm i finally found something about the chipset... and in fact, this machine is more a PS/2 model 30 8086 clone than an AT.
            http://www.bitsavers.org/components/chipsAndT … orm_Catalog.pdf

            you think sanyo did the choice to only limit extra ram as ems only ?
            sad they don't say anything about this in their manual.

            which driver i can try to verify this ?
            i tried qram 2.02, but it was a fail, it hangs when running optimize the first time.
            and i'm not very familiar with ems things...

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