Kaypro II repair - CP/M

This is a discussion on Kaypro II repair - CP/M ; The point of my post was not to diagnose the problem, but to suggest that Andrea would benefit from being able to diagnose the problem herself. She (or anyone) can do so, to the extent of their knowledge and tools. ...

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Thread: Kaypro II repair

  1. Re: Kaypro II repair

    The point of my post was not to diagnose the problem, but to suggest
    that Andrea would benefit from being able to diagnose the problem
    herself. She (or anyone) can do so, to the extent of their knowledge
    and tools. My friend and colleage Allison can diagnose better than I,
    but I can make some general points in reply.

    no.s...@ wrote:
    > Herb Johnson posted


    > >I don't have the schematics in front of me, but typically this kind of
    > >design has a bunch of logic chips which display memory contents in
    > >video;

    >
    > Not the case for a kaypro. Kaypro has a seperate video ram and
    > applications (processor ram). However if the Z80 is doing nothing
    > the video ram with never be updated.


    This illustrates the different ways these microcomputers can produce
    video. A reading of the schematic and the technical documentation
    provide guidance as to which circuits can be ignored, which ones to
    check. When you've read a lot of schematics, these things start to add
    up.

    > >Now, the video side is working...and stable...- you have a display of memory


    > Also since the 6845 has to be programmed to get to that state (does
    > not power up to that by default) the Z80 must be doing something
    > and either getting lost or cant talk to the display ram to update it.


    Again, more knowledge about the 6845 leads to understanding and more
    clues.

    > > No "logic probe" work will easily determine what
    > >it is doing or why. A logic probe is not an oscilloscope, it will not
    > >show you timing and sequence of logic signals.


    > I disagree. A scope is the tool for hunting for logic that is sorta
    > there. A logic probe is for those signals that are present or absent.
    > The likelyhood of the latter in a known design that did work at one
    > time is very high. So the likely circuit fault is maybe only one gate
    > that has died.


    This is a matter of taste and of experience. An experienced person
    like Allison knows to look for "bad logic", rather than check for
    logic activity. One can use the oscillscope as a logic probe. Allison
    could probably diagnose with an LED and resistor to ground if
    necessary!

    > >It's hard to say from this point "here is what you should do". The
    > >problem is you don't have any equipment and you don't have much
    > >digital circuit knowledge....


    > Clearly there is a should do. One is know how the system operates and
    > methodically proceed from that understanding to see what is being done..


    We are not in disagreement. Allison goes on to diagnose based on the
    information given (a stable video display) and her better knowledge of
    the Kaypro and what the circuit is doing. She also offers more actions
    to be taken to yield more clues; and possible failures.

    I declined to do this because I was making a larger point. But one can
    also do what you (Andrea) has done; ask for help, get some feedback,
    act on it, show results, ask for more help.....Nothing wrong with
    that, but as I said: it's a learning opportunity if you invest in
    learning more about these devices and circuits. Allison suggests that,
    as a practical matter, problems are often a failed part at one point:

    > My expereince with many dozens of
    > machines and board is all it takes is a ... part that failed with time
    > or some side effect of
    > mishandling in it's life before being inserted in the board.
    >

    [Regarding repairs and diagnosis...]
    > It's an acquired skill for some and for others its' magic and the
    > skill eludes them. Troubleshooting is a mystery novel, you know the
    > ending and the victims but what happens in between is process,
    > knowledge and interpreting the clues that are there.
    >
    > Allison


    Actually, I'd say it's more like a mystery novel YOU ARE WRITING. It's
    based on "true facts" but the facts are not apparent. Even the ending
    and victims are not clear. Many enjoy reading detective novels because
    they enjoy the process and interpretation, or they have a sense of
    justice. Likewise, many enjoy repair and diagnosis for the challenge,
    or to return equipment to good use.

    Andrea replies later that swapping chips "is not the best way to
    repair computers". There's nothing wrong with doing that. BUT, it goes
    faster when you know which chips to swap, and why. And, if there are
    any computers where one can learn how they work down to the chip, it's
    computers which first ran CP/M!

    I'm glad Andrea got some encouragements, as well as some specific
    "where to go's". The advice and points apply in general, at least...in
    the CP/M zone...

    Herb Johnson
    be de be de be de be de...
    retrotechnology.com

  2. Re: Kaypro II repair

    Herb Johnson writes:

    >no.s...@ wrote:


    >> Also since the 6845 has to be programmed to get to that state (does
    >> not power up to that by default) the Z80 must be doing something
    >> and either getting lost or cant talk to the display ram to update it.


    >Again, more knowledge about the 6845 leads to understanding and more
    >clues.


    But:

    If you look at the shematics:

    http://myretrocomputing.altervista.o...yro_II_crt.png

    there is *no* 6845-IC to be programmed.

    A simple oszillator at the upper left corner and a chain of
    TTL-dividers make the video-Timing.

    The CPU has a seperate oszillator:

    http://myretrocomputing.altervista.o...pro_II_cpu.png

    yours, Holger

  3. Re: Kaypro II repair

    On Tue, 16 Sep 2008 07:57:57 +0000 (UTC), Holger Petersen
    wrote:

    >Herb Johnson writes:
    >
    >>no.s...@ wrote:

    >
    >>> Also since the 6845 has to be programmed to get to that state (does
    >>> not power up to that by default) the Z80 must be doing something
    >>> and either getting lost or cant talk to the display ram to update it.

    >
    >>Again, more knowledge about the 6845 leads to understanding and more
    >>clues.

    >
    >But:
    >
    >If you look at the shematics:
    >
    > http://myretrocomputing.altervista.o...yro_II_crt.png
    >
    >there is *no* 6845-IC to be programmed.


    Rats, Thats one of the difernce between the II and the 2.

    The 4/84 dioes use the 6845.

    >
    >A simple oszillator at the upper left corner and a chain of
    >TTL-dividers make the video-Timing.
    >
    >The CPU has a seperate oszillator:
    >
    >http://myretrocomputing.altervista.o...pro_II_cpu.png


    Even this we have more information. The divider chain of the Video
    is working so we know there is clock there. However that doent mean
    the CPU clock or some part of the logic on that page is fully there.

    Allison


    >
    >yours, Holger



  4. Re: Kaypro II repair

    andrea wrote:
    >
    > I am not sure I understand how to make this. As I've already said, I
    > have only very basic knowledge of electronics, so this sounds somewhat
    > arcane to me. I have a digital tester (multimeter?) that can test AC
    > too, after the check I noticed this strange behavior: at power up
    > sometimes on the address bus pins (1-5, 30-40) I get 1.6V, while on
    > clock pin (6) I get 0V. After pressing the reset button address bus pins
    > go to about 6V while clock goes 8.8V. Sometimes instead at power up I
    > get 2.4V on the address bus pins and 8.8V on clock. If I press the reset
    > none of these values change. I guess this is not normal... is it?
    >
    > Andrea
    >

    Seeing either 0 volts or 8.8 volts on the clock is probably wrong. The
    clock should be a square wave between 0 and ~5 volts. 0 volts could mean
    the oscillator is not running. 8.8 volts adds that the 5 volt power supply
    is may not be correct.

    Since you are probably measuring with a DC voltmeter, it is difficult to
    make anything out of the values you read, but the values are suspect.


  5. Re: Kaypro II repair

    joe wrote:

    > Seeing either 0 volts or 8.8 volts on the clock is probably wrong. The
    > clock should be a square wave between 0 and ~5 volts. 0 volts could mean
    > the oscillator is not running. 8.8 volts adds that the 5 volt power supply
    > is may not be correct.
    >
    > Since you are probably measuring with a DC voltmeter, it is difficult to
    > make anything out of the values you read, but the values are suspect.


    I am using another voltmeter and I now I find 10.2V or 0V. Of course, I
    am using it in the AC mode, as suggested by Glen, so I guess now the 10V
    value is fine, PSU is ok.

    Andrea


    --

    http://myretrocomputing.altervista.org

  6. Re: Kaypro II repair

    joe wrote:
    (snip)

    > Seeing either 0 volts or 8.8 volts on the clock is probably wrong. The
    > clock should be a square wave between 0 and ~5 volts. 0 volts could mean
    > the oscillator is not running. 8.8 volts adds that the 5 volt power supply
    > is may not be correct.


    If it measures the average of the absolute value of the AC
    coupled input and displays RMS you could get up to about 8V.

    > Since you are probably measuring with a DC voltmeter, it is difficult to
    > make anything out of the values you read, but the values are suspect.


    The usual electronic voltmeter is AC coupled (a capacitor) in AC
    mode, so it will indicate a changing signal (large reading) or
    static signal (close to zero). In DC mode it will give the
    average value. Both are useful for such debugging.

    -- glen



  7. Re: Kaypro II repair

    no.spam@no.uce.bellatlantic.net wrote:
    (snip)

    > Most of that may not easily apply to the kaypro. the clock derivation
    > for video, serial and CPu are different.


    This reminds me of the C64, which included the schematic in the box.

    It takes just a few seconds to see what they did in the design:

    The display logic is in one corner, (triangle in the matrix sense),
    the processor logic in the other, and a PLL in the middle.

    It seems that originally they had separate clocks for the two, but
    there was enough leakage that was visible in the display, especially
    if they are close to the ratio of integers. With the PLL they are
    phase locked, so no patterns slowly crawling on the screen.

    -- glen


  8. Re: Kaypro II repair

    On Sep 16, 3:08 pm, glen herrmannsfeldt wrote:
    > joe wrote:
    >
    > (snip)
    >
    > > Seeing either 0 volts or 8.8 volts on the clock is probably wrong. The
    > > clock should be a square wave between 0 and ~5 volts. 0 volts could mean
    > > the oscillator is not running. 8.8 volts adds that the 5 volt power supply
    > > is may not be correct.

    >
    > If it measures the average of the absolute value of the AC
    > coupled input and displays RMS you could get up to about 8V.
    >
    > > Since you are probably measuring with a DC voltmeter, it is difficult to
    > > make anything out of the values you read, but the values are suspect.

    >
    > The usual electronic voltmeter is AC coupled (a capacitor) in AC
    > mode, so it will indicate a changing signal (large reading) or
    > static signal (close to zero). In DC mode it will give the
    > average value. Both are useful for such debugging.
    >
    > -- glen


    As an engineer, I find it odd to use either an AC or a DC voltmeter,
    to look at logical signals. Seems to me different meters would display
    different results, based on their response to megahertz-speed digital
    signals. For sure, even if the AC meter "says" 8 volts" there is NOT
    an 8-volt signal there.

    But now I'm curious. Do people REALLY use DC or AC voltmeters to look
    at TTL type logic and microprocessors? And get consistent results?
    That they can explain simply to someone else less knowledgeable?
    Expalin them to me, maybe I know too much.

    Herb Johnson
    retrotechnology.com

  9. Re: Kaypro II repair

    Herb Johnson wrote:
    >

    .... snip ...
    >
    > As an engineer, I find it odd to use either an AC or a DC
    > voltmeter, to look at logical signals. Seems to me different
    > meters would display different results, based on their response
    > to megahertz-speed digital signals. For sure, even if the AC
    > meter "says" 8 volts" there is NOT an 8-volt signal there.
    >
    > But now I'm curious. Do people REALLY use DC or AC voltmeters to
    > look at TTL type logic and microprocessors? And get consistent
    > results? That they can explain simply to someone else less
    > knowledgeable? Expalin them to me, maybe I know too much.


    I suspect they just don't have a scope, or are ignorant about
    electricity. If they have to use a DC voltmeter to check clock
    amplitude, I suggest a diode driving a small capacitor (say 0.001
    uF, at a guess) and measure what shows up there. That should be a
    fairly reliable 5V dc.

    --
    [mail]: Chuck F (cbfalconer at maineline dot net)
    [page]:
    Try the download section.

  10. Re: Kaypro II repair

    *Herb Johnson* wrote on Wed, 08-09-17 00:15:
    >I find it odd to use either an AC or a DC voltmeter, to look at logical
    >signals.


    I'd say all you can see is whether a line is static or has changes of
    level. In many cases this can tell you a lot and if a voltmeter is all
    you have (or is all you have in your shirt pocket right now) it's that
    or nothing.


  11. Re: Kaypro II repair


    "Herb Johnson" wrote in message
    news:c94fbb08-0a6e-453b-b53c-2fb08aa4bb59@l42g2000hsc.googlegroups.com...
    > On Sep 16, 3:08 pm, glen herrmannsfeldt wrote:
    >> joe wrote:
    >>
    >> (snip)
    >>
    >> > Seeing either 0 volts or 8.8 volts on the clock is probably wrong. The
    >> > clock should be a square wave between 0 and ~5 volts. 0 volts could
    >> > mean
    >> > the oscillator is not running. 8.8 volts adds that the 5 volt power
    >> > supply
    >> > is may not be correct.

    >>
    >> If it measures the average of the absolute value of the AC
    >> coupled input and displays RMS you could get up to about 8V.
    >>
    >> > Since you are probably measuring with a DC voltmeter, it is difficult
    >> > to
    >> > make anything out of the values you read, but the values are suspect.

    >>
    >> The usual electronic voltmeter is AC coupled (a capacitor) in AC
    >> mode, so it will indicate a changing signal (large reading) or
    >> static signal (close to zero). In DC mode it will give the
    >> average value. Both are useful for such debugging.
    >>
    >> -- glen

    >
    > As an engineer, I find it odd to use either an AC or a DC voltmeter,
    > to look at logical signals. Seems to me different meters would display
    > different results, based on their response to megahertz-speed digital
    > signals. For sure, even if the AC meter "says" 8 volts" there is NOT
    > an 8-volt signal there.
    >
    > But now I'm curious. Do people REALLY use DC or AC voltmeters to look
    > at TTL type logic and microprocessors? And get consistent results?
    > That they can explain simply to someone else less knowledgeable?
    > Expalin them to me, maybe I know too much.
    >
    > Herb Johnson
    > retrotechnology.com


    I have the benefit of many years of troubleshooting electrical and
    electronic gear, from tubes and relays into the earliest of "solid state".
    So do many of the group's participants. What was not considered, or at
    least mentioned to date, is that measuring expected DC levels in AC mode
    will show higher levels due to circuit and measurement equipment
    capacitance, approaching 200% if ripple is excessive.

    In my years of "shooting bugs" on micros I found probably more than 90% of
    problems using a Tektronix Logic Probe. Realize of course that this was
    relatively low frequency clocking (typically less than 12 MHz.), but
    transitions of address, data, and control lines were clearly indicated by
    alternate flashes of the HIGH/LOW LEDs, and data/status could be captured
    using the optional TRIGGER input of the logic probe to sync a transition to
    a desired clocking input.

    In Andrea's case, a cheap used 'scope would be both an boon to her
    understanding, as well as a useful tool to determine what's happening on the
    power supply side (excessive AC ripple or unregulated output?), ADDRESS line
    transitions (showing that the processor is functioning, and that required
    address lines are functional), DATA line transitions (showing that one or
    more data lines aren't stuck), and CONTROL line status (giving an indication
    of what mode the processor should be in during an operation).

    As mentioned by others previously, you have to know what you're looking for
    before you can determine what ain't happening!

    My 2 cents... here's a nickel, keep the change!



  12. Re: Kaypro II repair

    Herb Johnson wrote:
    (snip)

    > But now I'm curious. Do people REALLY use DC or AC voltmeters to look
    > at TTL type logic and microprocessors? And get consistent results?
    > That they can explain simply to someone else less knowledgeable?
    > Expalin them to me, maybe I know too much.


    The OP indicated he had a DVM but not a scope.

    The processor either is or isn't running, and you can
    tell that with a DVM. Some of the address lines should
    be changing. With a scope that is about all you are
    likely to learn, anyway.

    For debugging a new design, a scope with multiple inputs,
    at least such that you can trigger off one signal and
    monitor another, would help. That allows one to find
    possible setup/hold violations for example.

    In this case, the design is already known to work.
    While some timing problems might be left, most should have
    been resolved. (Except possibly for capacitor drift.)

    If the clock is running and the processor isn't, measuring
    the AC and DC voltage on all the inputs should track down
    why it isn't running.

    A scope would be nice, though.

    -- glen


  13. Re: Kaypro II repair

    glen herrmannsfeldt wrote:

    > joe wrote:
    > (snip)
    >
    >> Seeing either 0 volts or 8.8 volts on the clock is probably wrong. The
    >> clock should be a square wave between 0 and ~5 volts. 0 volts could mean
    >> the oscillator is not running. 8.8 volts adds that the 5 volt power
    >> supply is may not be correct.

    >
    > If it measures the average of the absolute value of the AC
    > coupled input and displays RMS you could get up to about 8V.
    >
    >> Since you are probably measuring with a DC voltmeter, it is difficult to
    >> make anything out of the values you read, but the values are suspect.

    >
    > The usual electronic voltmeter is AC coupled (a capacitor) in AC
    > mode, so it will indicate a changing signal (large reading) or
    > static signal (close to zero). In DC mode it will give the
    > average value. Both are useful for such debugging.
    >
    > -- glen


    I took 2 DVMs and 3 analog voltmeters and used them to measure a 2.5 MHz 5
    volt peak to peak square wave.

    I measured AC volts.

    The two DVMs and one analog meter read basically 0.
    One analog meter read full scale on any range. Obviously its accuracy for
    high frequencies is questionable.
    One analog meter read 2.5 volts. (Triplett 630)

    Either my meters are toast, or trying to make any sense of readings from
    that kind of signal is questionable at best.

    Andrea could learn much more using an oscilloscope.



  14. Re: Kaypro II repair

    glen herrmannsfeldt writes:

    >The OP indicated he had a DVM but not a scope.

    ^^
    If not in italy, "Andrea" sounds female to me (as a german :-)


    >The processor either is or isn't running, and you can
    >tell that with a DVM. Some of the address lines should
    >be changing. With a scope that is about all you are
    >likely to learn, anyway.


    I'd look on the M1-signalof the Z80.
    And: Once I repaired a PC, where the RESET-'push-button'
    was stuck in the closed position...

    So: what is the state of the control-signals of the Z80?

    Yours, Holger

  15. Re: Kaypro II repair

    On Wed, 17 Sep 2008 09:00:35 +0000 (UTC), I waved a wand and this
    message magically appears in front of Holger Petersen:

    > If not in italy, "Andrea" sounds female to me (as a german :-)


    Andrea's a gender neutral name.
    --
    http://www.munted.org.uk

    Fearsome grindings.

  16. Re: Kaypro II repair

    andrea wrote:

    > gek wrote:
    >
    >
    >
    >>Your problem is most likely with the DRAM, or refresh circuitry
    >>(largely built around a 74164) Since you've swapped the DRAM, I'd
    >>take a look at the power supply stability and DRAM support IC's
    >>(74157, 8216, 74164).

    >
    >
    > Thanks for this advice.
    >
    > By the way, yesterday I could show the schematics to a person that has
    > far much better knowledge of those old computers than me and he told me
    > basically the same things that were said by the various posters of this
    > thread. In short, it could be anything. So I will finish my plan of
    > swapping the last 5 or so chips then, if I get no positive feedback, I
    > will start to learn how old computer circuitry operate and to find an
    > oscilloscope for this purpose.
    >
    > Regards
    > Andrea
    >
    >
    >
    >
    >



    I'm coming into this real late, but wanted to ask if you got your Kaypro
    running yet?

    Did anyone mention this one?

    The most common problem I recall dealing with was the power supply
    connector. They were simply crimped on, and after a while corrossion
    between the wires and connector would cause problems.
    Soldering the pins to the wires usually cured all kinds of woes.

    Richard Lamb

  17. Re: Kaypro II repair

    "Richard" wrote:

    > Did anyone mention this one?
    >
    > The most common problem I recall dealing with was the power supply
    > connector. They were simply crimped on, and after a while corrossion
    > between the wires and connector would cause problems.
    > Soldering the pins to the wires usually cured all kinds of woes.


    I did... several years ago, in answer to someone else.

    I am aware of corrosion, since I live near the Atlantic Ocean.

    One symptom of corrosion is when a computer do not work when it is wet, but
    run without any problem when it is dry...

    I have a file dealing with corrosion, if someone is interested.

    Yours Sincerely,
    Mr. Emmanuel Roche, France




  18. Re: Kaypro II repair

    Richard wrote:

    > I'm coming into this real late, but wanted to ask if you got your Kaypro
    > running yet?


    Not yet, at the moment I am waiting to get somebody with an oscilloscope
    to check it, that's the most reasonable thing to do at this point.


    --

    http://myretrocomputing.altervista.org

  19. Re: Kaypro II repair

    andrea wrote:
    > Richard wrote:
    >
    >
    >>I'm coming into this real late, but wanted to ask if you got your Kaypro
    >> running yet?

    >
    >
    > Not yet, at the moment I am waiting to get somebody with an oscilloscope
    > to check it, that's the most reasonable thing to do at this point.
    >
    >


    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?

  20. Re: Kaypro II repair

    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

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