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Thread: Compatible CPU for Kaypro 2X?

  1. #1
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    Default Compatible CPU for Kaypro 2X?

    I have a Kaypro 2X which I believe has a bad CPU (the legs are noticeably corroded and the computer doesn't boot properly). However, the only Z80 I can seem to find is this one, a 6MHz part:

    https://www.ebay.com/itm/Zilog-Z80-Z...ss!18951!US!-1

    Would this CPU work as a Z80A replacement, or do I have to find an actual Z80A?

  2. #2
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    For Z80s, faster will pretty much always work in a slower system. The one in that picture looks suspiciously like a relabel, the text is less consistent than genuine Zilog parts, at least from the picture.

    Jameco has the Z80A (4 MHz part) for $2.65:

    https://www.jameco.com/z/Z80A-Major-...CPU_35596.html

  3. #3
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    Z80As were about 0.75 each back in the day for OEMs.

    Note that Z8400(NMOS) is the "official" family name, with variants, such as Z84C00 (CMOS part). Also, Zilog suffixes the part with the speed rating, so that Z840004 is an NMOS Z80 rated at 4MHz, while a Z84C0008 is a CMOS Z80 rated for 8 MHz operation.

    If you're really desperate, I'll got a few "pulls".

  4. #4

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    For the fun of it I tried the 20 MHz Zilog Z84C0020PEC in my Kaypro and it works fine (at original speed ofcourse)

    They came form an UK seller for about 7 Euro's a piece

  5. #5
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    I ended up trying the 6MHz part I linked for now, as Jameco's extra charge for orders under $15 meant I'd be paying just as much if not a little more to order one from them. I'm hoping changing the CPU might change the symptoms of my machine so I can get closer to fixing it.

  6. #6
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    FWIW, I've found that replacing the CPU in most cases accomplishes little. I hope your case turns out better.

  7. #7
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    It's the only part that's noticeably in ill health so it makes sense to me as a starting point.

  8. #8
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    Quote Originally Posted by Chuck(G) View Post
    FWIW, I've found that replacing the CPU in most cases accomplishes little. I hope your case turns out better.
    Yeah, agree with Chuck.

    In my 'kaypro' experience, I've had a bad CPU but it wasn't the only bad part.. Whatever killed the CPU also killed a few custom, and irreplaceable, IC's. The Z80's don't generally die on their own without something causing it, and whatever that was, probably killed other things along the way. If you're lucky, they didn't take out the Custom Gate Arrays, but if they did, it's pretty much game over (unless you have the knowledge to reproduce those with custom chips, I guess). Luckily the Z80 is cheap (and socketed) so it's not a big deal to swap it out.
    -- Brian

    Working Systems: Apple IIe/II+/Mac+/Mac 512k, Atari 800/520STFM, Commodore 64/Amiga 3000/SX-64, IBM PS/1 2121-B82, Kaypro II, Tandy 1000 SX, TI-99/4A, TRS-80 Model 4 GA
    Project Systems: Amstrad PCW 8256, Kaypro 2/84 (Bad Chips: 81-194, 81-189).

  9. #9
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    Unfortunately swapping the Z80 didn't change anything (but I'm still glad I did as the old Mostek Z80 was pretty gross looking). However, I noticed that a chip seems to be straight up missing from my board, after looking at images of other very similar Kaypro boards online.

    The chip is above the WDC branded chip, marked "Z80A PIO":

    http://www.nightfallcrew.com/wp-cont...4/IMG_1693.jpg

    I don't have a clue what this chip does but could its absence be causing me issues?

  10. #10

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    The PIO provides an interface to the RTC and modem, and usually it's absence doesn't prevent CP/M from running (boards were left with PIO, RTC, and modem un-populated for the "economy" versions).

    I don't think I have a description of what problems you are seeing. Can you describe what's wrong?

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