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Thread: Imsai 8080

  1. #1

    Default Imsai 8080

    My lastest (and probably greatest although I did find an Intel 4004 once) find:







    What needs to go where?

    This is as I found it. I'm not sure if I have a CPU though the last picture is a Z80 with support logic. I'll make a list of the cards when I get a few minutes.
    Last edited by hexsane; December 17th, 2010 at 09:47 PM. Reason: link update

  2. #2

    Default

    Hi
    It looks like the Z80 board is a universal IMSAI/ALTAR board. The
    8 pin connector on the right top would be used to connect the
    front panel of the ALTAR while the 16 pin socket near it would
    go to the IMSAI front panel. This would require that it be connect
    to the first socket behind the front panel.
    The other boards should not have any particular order. I'd check
    each one at a time, being ready to turn the power of quickly.
    Some recommend connecting things through a 60W light the first time.
    Others recommend slowly powering up with a variac. Some recommend
    both.
    If you can get the main chassis to power up without blowing a fuse
    or anything, I recommend plugging each board in one at a time.
    Turn the power on for the count of 3 seconds. Then feel all the caps
    for any that are hot. If none are hot, increase to 10 seconds and check
    again.
    Any smoke should indicate removing the power right away.
    Once you have the cpu card working on the front panel, you can start
    checking out the RAM boards.
    Some of the other boards, I'm not sure what they are. I'd need closer
    inspection and part numbers of any major parts.
    Dwight

  3. #3

    Default

    Card List:

    Digital Systems Bus Interface HB-1.4
    CCS Model 2032 32k Static RAM
    Dual Channel RS232 Serial I/O INTERFACER1 CompuPro Godbout
    MIO REV 2
    Card that looks identical to the MIO but not marked.
    BOB MULLEN TB-2 Buss Extender / Prototyping Board.
    2x D.R.C. EPROM cards. (1 is missing parts)
    S.D. SALES by MICRONIX (z80 CPU card)
    3x ECONORAM II 8k Card
    PIO REV 2 IMSAI
    RAM-4A REV 2
    TPS 100B A. SZERLIP 1977 (Attaches to a rotatory switch on the back of the IMSAI with labels for EPROMs (2708, 2716)

    A pin is missing from the header that fits on the CPU. I have one in a bin so that will be my first fix.

  4. #4

    Default

    Hi
    The Digital Systems board goes with the disk system
    that was one of the first to be used on the S100.
    You need the box that has the controller and one or two
    SA800 drives.
    I have one of these systems. It is cool in that you don't
    need a boot ROM. On power up, the disk system will
    DMA the boot sector into RAM. All one does then is hit
    RUN ( If the disk is CP/M then it is up and running ).
    Check out the following for more information:
    http://www.retrotechnology.com/dri/microcode.html
    Dwight

  5. #5

    Default

    Quote Originally Posted by hexsane View Post
    Card List:

    Digital Systems Bus Interface HB-1.4
    CCS Model 2032 32k Static RAM
    Dual Channel RS232 Serial I/O INTERFACER1 CompuPro Godbout
    MIO REV 2
    Card that looks identical to the MIO but not marked.
    BOB MULLEN TB-2 Buss Extender / Prototyping Board.
    2x D.R.C. EPROM cards. (1 is missing parts)
    S.D. SALES by MICRONIX (z80 CPU card)
    3x ECONORAM II 8k Card
    PIO REV 2 IMSAI
    RAM-4A REV 2
    TPS 100B A. SZERLIP 1977 (Attaches to a rotatory switch on the back of the IMSAI with labels for EPROMs (2708, 2716)

    A pin is missing from the header that fits on the CPU. I have one in a bin so that will be my first fix.

    I noticed the twisted-pair of wires on the right-hand side connecting to the front panel board, but I can't see where it goes. This is the power switch wire and if it's wired "stock", it's connected directly to the power supply board which means it's carrying mains voltage.

    IMHO, this is the worst design choice ever because it's mixing line voltage and logic voltage in close proximity *and* it's not shielded. There were two common fixes: First is to disable the front panel switch and use a switch on the back panel to control the power. The second is to convert the switching to low voltage with a relay and put a "master" power switch on the back panel. This at least preserves the use of the front panel power switch but requires a small relay and transformer to power the relay (like 120v-6vac).

    My IMSAI came with the first modification but I converted it to the second to preserve the functionality of the front panel power switch. There are probably designs which don't require the use of a second step-down transformer, but I used what I had "in stock".

  6. #6

    Default

    Quote Originally Posted by Dwight Elvey View Post
    Hi
    The Digital Systems board goes with the disk system
    that was one of the first to be used on the S100.
    You need the box that has the controller and one or two
    SA800 drives.
    I have one of these systems. It is cool in that you don't
    need a boot ROM. On power up, the disk system will
    DMA the boot sector into RAM. All one does then is hit
    RUN ( If the disk is CP/M then it is up and running ).
    Check out the following for more information:
    http://www.retrotechnology.com/dri/microcode.html
    Dwight
    Hi
    Somehow I posted this to the wrong group.

    http://news.mydrivers.com/pages/imag...4445_28157.jpg

    The Digital Systems drive is on the bottom of the stack.
    Most were blue to match the IMSAI but some were a light brown
    as well. You need to keep an eye out for these to get something
    to match the interface card.
    Dwight

  7. #7

    Default

    I went back to where I found the IMSAI and did another search but didn't find anything. Unfortunately this is a recycling place and that drive system probably ended up being chewed up or shipped to a processor.

    I'm finishing a few projects around here before diving into the IMSAI hopefully I'll get to it later this week.

    -Matt

  8. #8

    Default

    Quote Originally Posted by hexsane View Post
    I went back to where I found the IMSAI and did another search but didn't find anything. Unfortunately this is a recycling place and that drive system probably ended up being chewed up or shipped to a processor.

    I'm finishing a few projects around here before diving into the IMSAI hopefully I'll get to it later this week.

    -Matt
    Hi
    I'd recommend hanging on the the interface card but get another
    floppy card that has the controller on the board. You'll need a
    ROM card to run it but it looks like you have one of those.
    Just keep an eye out for the Digital Systems drives. They
    show up every now and then without the interface card.
    Dwight

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