Kaypro II repair - CP/M

This is a discussion on Kaypro II repair - CP/M ; On Oct 8, 1:06 am, myem...@fattimie.i (andrea) wrote: > Richard wrote: > > Check the power connector to the main board. > > Solder it of it's not already. > > After 20-25 years, it's going to nead it anyway. ...

+ Reply to Thread
Page 3 of 3 FirstFirst 1 2 3
Results 41 to 43 of 43

Thread: Kaypro II repair

  1. Re: Kaypro II repair

    On Oct 8, 1:06 am, myem...@fattimie.i (andrea) wrote:
    > Richard wrote:
    > > Check the power connector to the main board.
    > > Solder it of it's not already.
    > > After 20-25 years, it's going to nead it anyway.

    >
    > > Worth a try?

    >
    > Yes, of course. But voltages were present on the board when I checked
    > them. Since yesterday I'm far from home so I can't do actually anything
    > to the kaypro, but if I will eventually succeed in repairing it I will
    > let the newsgroup know.
    >
    > Regards
    > Andrea
    >
    > --
    >
    > http://myretrocomputing.altervista.org



    Hi Andrea
    You mentioned that you'd replaced the EPROMs. Does that mean that
    you can program EPROMs?
    If so, there is another method of trouble shooting. One writes small
    bits
    of code the test things. This assumes that the CPU, address bus/data
    bus and
    the decoding for the EPROMs are working.
    I've used this method in the pass when nothing seemed to give an
    obvious
    indication of failure ( I do have a scope and know how to use it ).
    One should start really small. Assume that the RAM doesn't work.
    First
    experimental programs should be all in registers.
    First program might just be a jump to it self. One can look at the
    address
    lines to see if things are running as expected.
    Work up from there. Simple RAM test and I/O test. Once you find a
    reliable
    output method, you can use that a status for other experiments.
    I've not looked at the schematic but I assume that if it has DRAM, it
    uses
    the Z80's refresh. One can write a program that writes something to
    DRAM and then waits some time to ensure that it isn't lost ( 2 or 3
    seconds
    are usually enough ). This would check that the refresh was working.
    Each experiment may lead to the next experiment.
    If you can't get it working with a minimal program, try removing
    parts
    from the buses that are not needed for minimal operation. Things like
    bus buffers and then address decoders.
    Use some imagination. Read how the Z80 talks to the bus so you
    understand
    what to expect.
    It isn't hopeless but will take some work. A lot will be learned
    along the way.
    Dwight

  2. Re: Kaypro II repair

    dkelvey@hotmail.com wrote:


    > Hi Andrea
    > You mentioned that you'd replaced the EPROMs. Does that mean that
    > you can program EPROMs?


    Yes, I can...

    > If so, there is another method of trouble shooting.


    [snip]

    > It isn't hopeless but will take some work. A lot will be learned
    > along the way.


    Dwight, thanks for your interesting suggestions, but unfortunately I am
    not into microprocessors programming, anyway I think that on line I can
    find some resources that will help me to go down your path. It would be
    interesting, indeed.

    Regards
    Andrea



    --

    http://myretrocomputing.altervista.org

  3. Re: Kaypro II repair


    "andrea" wrote in message
    news:1in2fru.dnwb2a1abya3kN%myemail@fattimie.i...
    > Hello,
    > I am trying to repair a non working Kaypro II, board model 81-240-n,
    > boot eprom 81-232-n.
    > The computer powers up, but the screen gets filled with garbled
    > characters that keep blinking in a dual pattern, always the same, the
    > reset button has no effect, drives lights stay on. Nothing more happens.
    > I've already succesfully tested the Z80 chips (CPU, PIOs, SIO) on
    > another Z80 based computer and they all work, RAM ICs (4264) and video
    > RAM(2114) seem to be all fine. Same goes for chargen and boot eproms.
    > Meanwhile I am desoldering some TTL ICs that I can test on other
    > equipents, so to make sure they are fine.
    > Does anyone familiar with this computer can give me any hints or
    > suggestion on what could be the faulty component?
    >
    > Thanks in advance
    > Andrea
    >
    >


    Andrea,

    Maybe a dumb question, but...

    Did you perform a visual inspection of the mainboard with a magnifying
    glass? Cracked traces/solder, debris shorting adjacent traces, black
    corrosion on IC pins/sockets, blown caps, etc? Sometimes you need a
    magnifying glass to find these.

    -J
    >
    > --
    >
    > http://myretrocomputing.altervista.org




+ Reply to Thread
Page 3 of 3 FirstFirst 1 2 3