IMSAI Troubleshooting hints, FAQs, etc. ? - CP/M

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Thread: IMSAI Troubleshooting hints, FAQs, etc. ?

  1. IMSAI Troubleshooting hints, FAQs, etc. ?

    I'm posting to see if anyone has seen or heard of troubleshooting guides or
    FAQs for the IMSAI 8080. I have one that seems to have a memory problem (I
    deposit fine, but examine doesn't show the right bits sometimes). Trying to
    figure out if it's my memory card or just balky switches.

    thanks ahead,

    -John



  2. Re: IMSAI Troubleshooting hints, FAQs, etc. ?

    My recollection is that examine is a DC coupled, unlatched steady-state
    function. So, if I recall, you can remove all cards except the CPU, do
    an "examine", and then take a piece of wire and jumper the data bus to
    ground and the front panel light should turn on and off as you touch and
    untouch ground (you might want to put a low-value resistor, 100 to 300
    ohms, in series with the ground lead for safety). This will let you
    "debug" the front panel and backplane to be sure that the problem is not
    in the IMSAI. Much more likely, it's a memory board problem.


    John Crane wrote:
    > I'm posting to see if anyone has seen or heard of troubleshooting guides or
    > FAQs for the IMSAI 8080. I have one that seems to have a memory problem (I
    > deposit fine, but examine doesn't show the right bits sometimes). Trying to
    > figure out if it's my memory card or just balky switches.
    >
    > thanks ahead,
    >
    > -John
    >
    >


  3. Re: IMSAI Troubleshooting hints, FAQs, etc. ?

    John Crane (at) wrote:
    > I'm posting to see if anyone has seen or heard of troubleshooting guides or
    > FAQs for the IMSAI 8080. I have one that seems to have a memory problem (I
    > deposit fine, but examine doesn't show the right bits sometimes). Trying to
    > figure out if it's my memory card or just balky switches.
    >
    > thanks ahead,
    >
    > -John


    There are many Web sites which have IMSAI information, or at least
    systems on display. A Web search will find them. Some discussion of
    IMSAI problems are in archives of this newsgroup comp.os.cpm, which are
    also online in various places.

    Problems with IMSAI front panel functions are common. It's likely the
    front panel, and the one-shots which set the timing on those particular
    functions of the front panel. One-shot means monostable multivibrator
    chip, a flip flop with an RC circuit to produce a pulse of a certain
    width when triggered. With age, the capacitor (C) changes value and the
    timing gets screwed up. You'll likely have to change the capacitors on
    the relevant one-shots. You'll need an oscilloscope to check the
    timing, and or a capacitance meter to check the caps (or just replace
    them outright).

    If you don't know what the above terms mean, or if you don't know how
    to go about doing these tests and repairs, you'll have to look around
    the Web or at bookstores for guides to electronic component repair.
    Local libraries often have older books about these sort of components
    (resistors, capacitors, logic circuits and so forth). It's 1970's
    technology after all.

    The first and foremost "guide" to the IMSAI are the IMSAI manuals. They
    describe the operation of each board's circuit, and a schematic and
    parts lists. The parts are still common today, or at least can be
    ordered from any electronic component distributor. The IMSAI manuals
    are available from online sources, and as photocopies which can be
    ordered from my Web site.

    In my opinion, the fun of owning an IMSAI is in restoring it. A recent
    thread about S-100 systems is that for some they have a virtue of being
    simpler than modern personal computers. They are built for repair, at a
    time when repair was expected over a lifetime of several years.

    Herb Johnson

    Herbert R. Johnson, voice 609-771-1503, New Jersey USA
    web site
    domain mirror
    ** hjohnson@njcc.com and njcc.com/~hjohnson are EXPIRED **
    my email address: hjohnson AAT retrotechnology DOTT com
    if no reply, wait & try: herbjohnson ATT comcast DOTT net
    "Herb's Stuff": old Mac, SGI, 8-inch floppy drives
    S-100 IMSAI Altair computers, docs, by "Dr. S-100"


  4. Re: IMSAI Troubleshooting hints, FAQs, etc. ?

    Thanks, Herb!

    I agree, a lot of the fun comes from restoring them. Heck, If I just wanted
    utility, I could have bought a much more powerful machine for a lot less
    money off the shelf.

    I know about aging caps, particularly tantalums. I've already ordered some
    replacements; I plan to "re-cap" the machine entirely. Even if an old cap
    is not dead, it will be soon - cheap preventive maintenance. Have not taken
    the front panel off yet; but just peering into it, it looks like all ceramic
    disc caps. I'll work on that next, thanks for the tip on the one shots. I
    have a Priority 1 64K dynamic RAM card (populated only to 48K). I've
    ordered a fresh new batch of chips and caps for it too. I seem to recall
    dynamic RAM cards were a bit touchy.

    -JOhn


    "Herb Johnson" wrote in message
    news:1138996381.828651.45840@g43g2000cwa.googlegro ups.com...
    > John Crane (at) wrote:
    > > I'm posting to see if anyone has seen or heard of troubleshooting guides

    or
    > > FAQs for the IMSAI 8080. I have one that seems to have a memory problem

    (I
    > > deposit fine, but examine doesn't show the right bits sometimes).

    Trying to
    > > figure out if it's my memory card or just balky switches.
    > >
    > > thanks ahead,
    > >
    > > -John

    >
    > There are many Web sites which have IMSAI information, or at least
    > systems on display. A Web search will find them. Some discussion of
    > IMSAI problems are in archives of this newsgroup comp.os.cpm, which are
    > also online in various places.
    >
    > Problems with IMSAI front panel functions are common. It's likely the
    > front panel, and the one-shots which set the timing on those particular
    > functions of the front panel. One-shot means monostable multivibrator
    > chip, a flip flop with an RC circuit to produce a pulse of a certain
    > width when triggered. With age, the capacitor (C) changes value and the
    > timing gets screwed up. You'll likely have to change the capacitors on
    > the relevant one-shots. You'll need an oscilloscope to check the
    > timing, and or a capacitance meter to check the caps (or just replace
    > them outright).
    >
    > If you don't know what the above terms mean, or if you don't know how
    > to go about doing these tests and repairs, you'll have to look around
    > the Web or at bookstores for guides to electronic component repair.
    > Local libraries often have older books about these sort of components
    > (resistors, capacitors, logic circuits and so forth). It's 1970's
    > technology after all.
    >
    > The first and foremost "guide" to the IMSAI are the IMSAI manuals. They
    > describe the operation of each board's circuit, and a schematic and
    > parts lists. The parts are still common today, or at least can be
    > ordered from any electronic component distributor. The IMSAI manuals
    > are available from online sources, and as photocopies which can be
    > ordered from my Web site.
    >
    > In my opinion, the fun of owning an IMSAI is in restoring it. A recent
    > thread about S-100 systems is that for some they have a virtue of being
    > simpler than modern personal computers. They are built for repair, at a
    > time when repair was expected over a lifetime of several years.
    >
    > Herb Johnson
    >
    > Herbert R. Johnson, voice 609-771-1503, New Jersey USA
    > web site
    > domain mirror
    > ** hjohnson@njcc.com and njcc.com/~hjohnson are EXPIRED **
    > my email address: hjohnson AAT retrotechnology DOTT com
    > if no reply, wait & try: herbjohnson ATT comcast DOTT net
    > "Herb's Stuff": old Mac, SGI, 8-inch floppy drives
    > S-100 IMSAI Altair computers, docs, by "Dr. S-100"
    >




  5. Re: IMSAI Troubleshooting hints, FAQs, etc. ?

    I built an IMSAI back in the 1970s and never did get dynamic ram cards
    to work correctly with the front panel functions. Booting and running
    cp/m from floppies worked fine. Static ram cards always worked with
    front panel functions. I thought the problems had something to do with
    deposit/examine interrupting the dynamic refresh cycles.

    John


  6. Re: IMSAI Troubleshooting hints, FAQs, etc. ?

    On 4 Feb 2006 05:31:18 -0800, "jjk439@gmail.com"
    wrote:

    >I built an IMSAI back in the 1970s and never did get dynamic ram cards
    >to work correctly with the front panel functions. Booting and running
    >cp/m from floppies worked fine. Static ram cards always worked with
    >front panel functions. I thought the problems had something to do with
    >deposit/examine interrupting the dynamic refresh cycles.
    >
    >John


    There were many Dram cards that worked fine in IMSAI or ALTAIR and
    likely just as many that didn't. Dram was still a mystery back then
    and some designs were robust and worked and a few were very poor.
    It was not so much a front pannel problem or bus level issue as
    just bad design. The best example was the MITS 88S4K that was
    later replaced with the 884MCD. Both worked but the S4K tended to be
    cranky and the MCD didn't work with most Z80 cards. Dram took a bad
    rap for all the bad designs and didn't recover until the 64k designs
    appeared using the 8202, 8203, 2964 and similar Dram controllers.


    Allison

  7. Re: IMSAI Troubleshooting hints, FAQs, etc. ?

    Thanks for the info everyone.

    My Priority 1 card ("The Expandable One") is 1980 vintage and has only
    75LSxx series chips with 4116s. No fancy Dram controllers here. This
    makes more sense to me now as the whole system, as I purchased it, came with
    dual 8in drives and a controller card, plus lots of software. It's previous
    owner probably didn't spend much time flipping the toggles. Looks like it's
    time to start shopping for a static card?

    -John


    wrote in message
    news:3oi9u11p7kjkstssocm4tu1otevqfc4nvd@4ax.com...
    > On 4 Feb 2006 05:31:18 -0800, "jjk439@gmail.com"
    > wrote:
    >
    > >I built an IMSAI back in the 1970s and never did get dynamic ram cards
    > >to work correctly with the front panel functions. Booting and running
    > >cp/m from floppies worked fine. Static ram cards always worked with
    > >front panel functions. I thought the problems had something to do with
    > >deposit/examine interrupting the dynamic refresh cycles.
    > >
    > >John

    >
    > There were many Dram cards that worked fine in IMSAI or ALTAIR and
    > likely just as many that didn't. Dram was still a mystery back then
    > and some designs were robust and worked and a few were very poor.
    > It was not so much a front pannel problem or bus level issue as
    > just bad design. The best example was the MITS 88S4K that was
    > later replaced with the 884MCD. Both worked but the S4K tended to be
    > cranky and the MCD didn't work with most Z80 cards. Dram took a bad
    > rap for all the bad designs and didn't recover until the 64k designs
    > appeared using the 8202, 8203, 2964 and similar Dram controllers.
    >
    >
    > Allison




  8. Re: IMSAI Troubleshooting hints, FAQs, etc. ?

    On Sat, 4 Feb 2006 10:42:19 -0600, "John Crane"
    wrote:

    >Thanks for the info everyone.
    >
    >My Priority 1 card ("The Expandable One") is 1980 vintage and has only
    >75LSxx series chips with 4116s. No fancy Dram controllers here. This
    >makes more sense to me now as the whole system, as I purchased it, came with
    >dual 8in drives and a controller card, plus lots of software. It's previous
    >owner probably didn't spend much time flipping the toggles. Looks like it's
    >time to start shopping for a static card?
    >
    >-John


    The P1 card was not from all I'd heard back then [1980s] a good
    design. Yes you can build a good card using 74LSxx and 4116 but it
    was all too often the power gridding was poor or the timing marginal.
    The worst hack I'd seen was using the propagation delay of gates for
    the RAS/ to CAS/ Timing. While it worked, it tended to go flaky with
    temp changes and not all boards worked right due to part variations
    and Dram tolerences. All of the really good cards were more reliable
    than static and lower power.


    Allison
    >
    >
    > wrote in message
    >news:3oi9u11p7kjkstssocm4tu1otevqfc4nvd@4ax.com...
    >> On 4 Feb 2006 05:31:18 -0800, "jjk439@gmail.com"
    >> wrote:
    >>
    >> >I built an IMSAI back in the 1970s and never did get dynamic ram cards
    >> >to work correctly with the front panel functions. Booting and running
    >> >cp/m from floppies worked fine. Static ram cards always worked with
    >> >front panel functions. I thought the problems had something to do with
    >> >deposit/examine interrupting the dynamic refresh cycles.
    >> >
    >> >John

    >>
    >> There were many Dram cards that worked fine in IMSAI or ALTAIR and
    >> likely just as many that didn't. Dram was still a mystery back then
    >> and some designs were robust and worked and a few were very poor.
    >> It was not so much a front pannel problem or bus level issue as
    >> just bad design. The best example was the MITS 88S4K that was
    >> later replaced with the 884MCD. Both worked but the S4K tended to be
    >> cranky and the MCD didn't work with most Z80 cards. Dram took a bad
    >> rap for all the bad designs and didn't recover until the 64k designs
    >> appeared using the 8202, 8203, 2964 and similar Dram controllers.
    >>
    >>
    >> Allison

    >



  9. Re: IMSAI Troubleshooting hints, FAQs, etc. ?

    Hi John
    You don't need to replace it all with static. Most times
    you are using the front panel, it is only a small amount
    of memory that you are working in. In your case, you
    might want to get 16K of static.
    The fellow that had it most likely started with some
    static memory years ago and over time upgraded to
    dynamic.
    One of the other things that often fail on front panels
    are the 7406 open collector drivers. These tend to
    get flakey and not drive with their full strength.
    Dwight

    John Crane (at) wrote:
    > Thanks for the info everyone.
    >
    > My Priority 1 card ("The Expandable One") is 1980 vintage and has only
    > 75LSxx series chips with 4116s. No fancy Dram controllers here. This
    > makes more sense to me now as the whole system, as I purchased it, came with
    > dual 8in drives and a controller card, plus lots of software. It's previous
    > owner probably didn't spend much time flipping the toggles. Looks like it's
    > time to start shopping for a static card?
    >
    > -John
    >
    >
    > wrote in message
    > news:3oi9u11p7kjkstssocm4tu1otevqfc4nvd@4ax.com...
    > > On 4 Feb 2006 05:31:18 -0800, "jjk439@gmail.com"
    > > wrote:
    > >
    > > >I built an IMSAI back in the 1970s and never did get dynamic ram cards
    > > >to work correctly with the front panel functions. Booting and running
    > > >cp/m from floppies worked fine. Static ram cards always worked with
    > > >front panel functions. I thought the problems had something to do with
    > > >deposit/examine interrupting the dynamic refresh cycles.
    > > >
    > > >John

    > >
    > > There were many Dram cards that worked fine in IMSAI or ALTAIR and
    > > likely just as many that didn't. Dram was still a mystery back then
    > > and some designs were robust and worked and a few were very poor.
    > > It was not so much a front pannel problem or bus level issue as
    > > just bad design. The best example was the MITS 88S4K that was
    > > later replaced with the 884MCD. Both worked but the S4K tended to be
    > > cranky and the MCD didn't work with most Z80 cards. Dram took a bad
    > > rap for all the bad designs and didn't recover until the 64k designs
    > > appeared using the 8202, 8203, 2964 and similar Dram controllers.
    > >
    > >
    > > Allison



  10. Re: IMSAI Troubleshooting hints, FAQs, etc. ?

    IMSAI update - for those of you following the thread...

    Being the packrat that I am... I managed to dig up an old Priority 1 catalog
    from Fall 1981. In the list of features of "The Expandable 1", one bullet
    point states "Supports IMSAI-type front panels".

    Also, I tested all the caps on the front panel, MPU, and the Expandable 1
    64K DRAM card. All tested ok. I did find one ceramic disc cap with a
    cracked case on the front panel board and replaced it anyway.

    Now, I'm beginning to think it may be a logic chip problem or a bus issue.
    I have an active terminator card installed between the front panel and the
    MPU. Is it ok to have it in that position?

    -John

    "John Crane" wrote in message
    news:EqCdndJmjdT2RHnenZ2dnUVZ_s-dnZ2d@pghconnect.com...
    > Thanks for the info everyone.
    >
    > My Priority 1 card ("The Expandable One") is 1980 vintage and has only
    > 75LSxx series chips with 4116s. No fancy Dram controllers here. This
    > makes more sense to me now as the whole system, as I purchased it, came

    with
    > dual 8in drives and a controller card, plus lots of software. It's

    previous
    > owner probably didn't spend much time flipping the toggles. Looks like

    it's
    > time to start shopping for a static card?
    >
    > -John
    >
    >
    > wrote in message
    > news:3oi9u11p7kjkstssocm4tu1otevqfc4nvd@4ax.com...
    > > On 4 Feb 2006 05:31:18 -0800, "jjk439@gmail.com"
    > > wrote:
    > >
    > > >I built an IMSAI back in the 1970s and never did get dynamic ram cards
    > > >to work correctly with the front panel functions. Booting and running
    > > >cp/m from floppies worked fine. Static ram cards always worked with
    > > >front panel functions. I thought the problems had something to do with
    > > >deposit/examine interrupting the dynamic refresh cycles.
    > > >
    > > >John

    > >
    > > There were many Dram cards that worked fine in IMSAI or ALTAIR and
    > > likely just as many that didn't. Dram was still a mystery back then
    > > and some designs were robust and worked and a few were very poor.
    > > It was not so much a front pannel problem or bus level issue as
    > > just bad design. The best example was the MITS 88S4K that was
    > > later replaced with the 884MCD. Both worked but the S4K tended to be
    > > cranky and the MCD didn't work with most Z80 cards. Dram took a bad
    > > rap for all the bad designs and didn't recover until the 64k designs
    > > appeared using the 8202, 8203, 2964 and similar Dram controllers.
    > >
    > >
    > > Allison

    >
    >




  11. Re: IMSAI Troubleshooting hints, FAQs, etc. ?


    John Crane (at) wrote:
    > IMSAI update - for those of you following the thread...
    >
    > Being the packrat that I am... I managed to dig up an old Priority 1 catalog
    > from Fall 1981. In the list of features of "The Expandable 1", one bullet
    > point states "Supports IMSAI-type front panels".
    >
    > Also, I tested all the caps on the front panel, MPU, and the Expandable 1
    > 64K DRAM card. All tested ok. I did find one ceramic disc cap with a
    > cracked case on the front panel board and replaced it anyway.
    >
    > Now, I'm beginning to think it may be a logic chip problem or a bus issue.
    > I have an active terminator card installed between the front panel and the
    > MPU. Is it ok to have it in that position?


    Hi
    For the edge rate of these systems, the location isn't critical but
    the terminators are generally placed at the back end of these systems.
    This would be proper termination of driver to load.
    I have one with active terminators myself but I've not fiddled
    with the adjustments. I don't have the instructions for it so
    I'm reluctant to touch a working unit.
    As was mentioned by one of the others, sometimes the oneshoots
    on the front panel are not correct. This is true, even if the capacitor
    is the correct value. One really needs to check the pulses with
    a scope to make sure they are the correct width. The Altairs had more
    issues with this than the Imsais.
    If the pulse widths are incorrect, one can use different timing
    resistors
    to bring things into spec.
    There is one other thing. There is a write strobe signal that is
    suppose
    to come through the front panel from the CPU card. There is a jumper
    on the CPU card to select if this comed directly from the CPU card or
    is through the front panel. I've seen cases where this line was not
    jumpered correctly that caused flakey operation. I forget the name of
    this signal. Maybe one of the others can tell you what it is.
    It is difficult to check out the front panels without an oscilloscope.
    To see if things are working correctly, you need to trigger based
    on the switches and watch the data and address lines.
    One last thing that I've seen is that the cable that runs from
    the CPU to the front panel has it's bits reversed. This causes all
    kinds of funny behavior.
    Dwight

    >
    > -John
    >
    > "John Crane" wrote in message
    > news:EqCdndJmjdT2RHnenZ2dnUVZ_s-dnZ2d@pghconnect.com...
    > > Thanks for the info everyone.
    > >
    > > My Priority 1 card ("The Expandable One") is 1980 vintage and has only
    > > 75LSxx series chips with 4116s. No fancy Dram controllers here. This
    > > makes more sense to me now as the whole system, as I purchased it, came

    > with
    > > dual 8in drives and a controller card, plus lots of software. It's

    > previous
    > > owner probably didn't spend much time flipping the toggles. Looks like

    > it's
    > > time to start shopping for a static card?
    > >
    > > -John
    > >
    > >
    > > wrote in message
    > > news:3oi9u11p7kjkstssocm4tu1otevqfc4nvd@4ax.com...
    > > > On 4 Feb 2006 05:31:18 -0800, "jjk439@gmail.com"
    > > > wrote:
    > > >
    > > > >I built an IMSAI back in the 1970s and never did get dynamic ram cards
    > > > >to work correctly with the front panel functions. Booting and running
    > > > >cp/m from floppies worked fine. Static ram cards always worked with
    > > > >front panel functions. I thought the problems had something to do with
    > > > >deposit/examine interrupting the dynamic refresh cycles.
    > > > >
    > > > >John
    > > >
    > > > There were many Dram cards that worked fine in IMSAI or ALTAIR and
    > > > likely just as many that didn't. Dram was still a mystery back then
    > > > and some designs were robust and worked and a few were very poor.
    > > > It was not so much a front pannel problem or bus level issue as
    > > > just bad design. The best example was the MITS 88S4K that was
    > > > later replaced with the 884MCD. Both worked but the S4K tended to be
    > > > cranky and the MCD didn't work with most Z80 cards. Dram took a bad
    > > > rap for all the bad designs and didn't recover until the 64k designs
    > > > appeared using the 8202, 8203, 2964 and similar Dram controllers.
    > > >
    > > >
    > > > Allison

    > >
    > >



  12. Re: IMSAI Troubleshooting hints, FAQs, etc. ?


    I've restored two IMSAIs where the front panel switches were
    flakey. You might want to check that before you go too much
    further. In one case, it was actually the solder joint between
    the switch and the PCB that was cracked. In the other, something
    internal to the switch was bad. I was able to test using the
    ROM monitor program in a Cromemco 16FDC. It showed that the RAM
    was good and that the LEDs on the front panel were good also.


  13. Re: IMSAI Troubleshooting hints, FAQs, etc. ?

    I just picked up a imsai 8080 and noticed they cut traces on the CPA.
    But on imsai.net he has a PDF that explains why they did this to
    upgrade them
    I cleaned the spiders out of mine and tried to fire her up and blew a
    chip on the MPU
    I have the book and it dosn't really help because alot of things have
    been changed threw the years and even thou I have REV 1 power supply
    and Backplane(motherboard) they have it totally hooked up different
    than in the book?
    Where can i get replacement chips and capacitors for this?
    If anyone can help me along restoring this it would be nice because I
    really don't know to much about electronic repair, I don't have an
    oscillascope but I do have a multimeter LOL.
    I was also told I should of brought it up with a variac to melt things
    back right but variacs are expensive


  14. Re: IMSAI Troubleshooting hints, FAQs, etc. ?

    Hi
    What chip blew? Also, what caps? It is unlikely to blow a chip
    unless the regulator isn't working but tantalum caps will often
    blow after some time sitting. If you have a T-03 type regulator
    on the board, check the connection between the case and the
    PC board. The screws here can get corroded and open this
    connection. This can cause all kinds of problems. If the ohm meter
    doesn't show zero ohms, remove the screws and clean any oxide.
    put them on tight but don't strip them.
    If a tantalum has failed, besides the smoke, it will short the
    power rail. Make sure that you have all the regulated voltages
    needed for the board.
    If you have an IMSAI with front panel, you should be able to
    fix most things with just a volt meter. It has single step
    capabilities.
    The only real problem is that the front panel may be flakey as well.
    Places like Jamco or HSC ( www.halted.com ) should have what
    you need.
    Dwight

    greenmeanie wrote:
    > I just picked up a imsai 8080 and noticed they cut traces on the CPA.
    > But on imsai.net he has a PDF that explains why they did this to
    > upgrade them
    > I cleaned the spiders out of mine and tried to fire her up and blew a
    > chip on the MPU
    > I have the book and it dosn't really help because alot of things have
    > been changed threw the years and even thou I have REV 1 power supply
    > and Backplane(motherboard) they have it totally hooked up different
    > than in the book?
    > Where can i get replacement chips and capacitors for this?
    > If anyone can help me along restoring this it would be nice because I
    > really don't know to much about electronic repair, I don't have an
    > oscillascope but I do have a multimeter LOL.
    > I was also told I should of brought it up with a variac to melt things
    > back right but variacs are expensive



  15. Re: IMSAI Troubleshooting hints, FAQs, etc. ?

    I had to get hex3 buffer IC replacement for the MPU.
    What I found weird is my power supply to the motherboard dosn't have
    the orange wires. Also the black and white wires goto different places
    on the MB than in the schematics? Was there different ways to wires
    these or upgrades?


  16. Re: IMSAI Troubleshooting hints, FAQs, etc. ?

    Hi
    In order to tell you where to get parts, you need to specify
    the part number. I don't know what a "hex3 buffer IC" is.
    Can you be more specific about the part number? I
    think you are talking about the hex 3 state buffer chips.
    Look on the web for the pinouts of the S-100 bus. Check
    the voltages on the supply pins with no boards plugged in.
    The wires used in your machine may not be the same
    or the back plane may not even be an original board.
    Many were replaced with newer low noise boards.
    The only way to be sure is to measure. Do note that the
    unregulated levels may be 2 to 6 volts higher than the
    specified levels. Unregulated 8 volts may be 10 volts
    with no load.
    Also, as a warning, there are voltages on opposite sides
    of the connector that if shorted will damage the connector.
    Place a piece of thin cardboard in the slot before measuring.
    A piece of cereal box, about 1 inch wide, works well. This will
    keep a slipped probe from shorting things out( speak from
    experience ).
    Dwight


    greenmeanie wrote:
    > I had to get hex3 buffer IC replacement for the MPU.
    > What I found weird is my power supply to the motherboard dosn't have
    > the orange wires. Also the black and white wires goto different places
    > on the MB than in the schematics? Was there different ways to wires
    > these or upgrades .



  17. Re: IMSAI Troubleshooting hints, FAQs, etc. ?

    The backplane is stock IMSAI EXP-22 and the same with the power supply
    REV1 IMS.
    I got the IC's Todd Fischer helped me cross reference them.


  18. Re: IMSAI Troubleshooting hints, FAQs, etc. ?


    greenmeanie wrote:
    > The backplane is stock IMSAI EXP-22 and the same with the power supply
    > REV1 IMS.
    > I got the IC's Todd Fischer helped me cross reference them.


    Hi
    Then it is best to not depend on wire color and measure
    the voltages at the S-100 edge connectors.
    Dwight


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