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Thread: OSBORNE Executive Boot Error

  1. #1
    Join Date
    Jul 2019
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    Montréal, QC
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    Default OSBORNE Executive Boot Error

    Hello People of the Vintage Computer Forum !

    An Osborne Executive was given to me recently, with documentation and disks.
    But I can't get it to boot. I get a "Boot Error. Press Enter to try again" message with all the disks I tried, with drive A and B.
    I cleaned and lubed the drives, no improvements.
    Power supply looks good 12v and 5v are there and don't seem to fluctuate.
    Not knowing what else I could do, I adjusted the speed of the motors to get a steady image with a lamp at 60 Hz (it wasn't steady before my adjustment, no idea if I made things worse by changing that, but hey, I had no other ideas...)

    I have no other floppy, or floppy drive known to work that I can test with.

    Before buying a floppy drive emulator : Any idea what else I could try in my troubleshooting ?
    Any known issue with the drives or controller that could cause that ?
    Does anyone have the documentation regarding the jumpers on the logic board ?

    Thanks,

    Yakeru

  2. #2
    Join Date
    Jun 2012
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    UK - Worcester
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    Default

    Start here with the documentation: http://www.bitsavers.org/pdf/osborne/executive/.

    Do you have any test equipment (e.g. multimeter, logic probe or oscilloscope)?

    Dave

  3. #3
    Join Date
    Jul 2019
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    Montréal, QC
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    Default

    Hello Daver2,

    Thanks for the documentation ! I have access to test equipment, including multimeter and oscilloscope yes.
    So if I interpret your answer correctly, I have to start probing the logic board and check the signals

    Ok, I will move the computer to a test bench and prepare the equipment. If you have any tip on where to start and/or most common faults, it would be greatly appreciated.
    Until then, I will start with checking the power supply and a few signals around the FDD Controler.

    Thanks,

    Yakeru

  4. #4
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    Jul 2019
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    Hello,

    So I probed here and there with my scope, especially PIN 30 on the floppy, and there is data going through when I press enter to boot.
    So, from what I can see, the disk spins, the head moves, and data is transmitted, so I suppose we can assume that the FDD, FDD controler and PSU are in working order.
    Would I see any data on pin 30 if the track 0 wasn't set properly ? It's the last thing I can think of.

    I ordered another set of floppies on eBay that have been tested, I will let you know what happens.

    Thanks

  5. #5
    Join Date
    Jul 2019
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    I entirely re-caped the machine, (PSU, MB, Screen, Floppies, ...) It might be overkill, but before doing that, the screen stopped working, and my vintage audio-amp started showing signs of needing a re-cap, so why not ...

    Now it's re-caped, and it won't hurt. But no improvements. The screen issue seems to be intermittent, it started working again while I was probing with my scope, and stopped working shortly after again.
    As for the boot error, still there, even with a set of freshly made and tested floppies.

    One question to you hardware gurus, might be a stupid question, but I know only the very basics : is the ground supposed to be live by design in that machine ?

    By default, when the components are layed flat on my table, everywhere I probe with the scope, I see 120V 60 Hz.
    If I clip the ground alligator of my scope to the ground of the logic board, or frame, it shorts (logical... if the ground is live, and my scope clip goes to earth...).
    If beforehand I connect the frame and ground of the board to Earth, then I get the correct readings on my scope, and since the clip of my scope and frame are now both the "same ground/earth" I can clip anywhere, it doesn't short anymore, actually, I don't need the clip, since it's the same ref.
    In both cases, live ground, or earth ground, the machine seems to work the same, that's what bothers me...

    Ground can be anything you want it to be, but live 120 ? And works the same whether it's live or earth ? There must be something very basic that I don't know or understand, or something very wrong with the PSU

    Thanks for your help

  6. #6

    Default

    Quote Originally Posted by Yakeru View Post
    If beforehand I connect the frame and ground of the board to Earth, then I get the correct readings on my scope, and since the clip of my scope and frame are now both the "same ground/earth" I can clip anywhere, it doesn't short anymore, actually, I don't need the clip, since it's the same ref.
    You see a potential-free design. Basically, the absolute potential behind a transformer is not known, only the voltage (potential difference) between the two outputs is. In other words, your GND is floating with regard to the house ground.

    This is a very dangerous situation. To avoid this, wall outlets have protective ground (the third wire), which provides the actual ground potential and prevents you from getting shocked on a metal case in case of a failure.

    You can buy transformers to turn any wall outlet into a potential-free outlet. These can be used to e.g. power an oscilloscope, allowing you to measure inside a potential-free power supply. Keep in mind that this is very dangerous, because it bypasses the safety! (The modern alternative are battery-powered oscilloscopes, which are potential-free by design.)

  7. #7
    Join Date
    Jul 2019
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    Hello Svenska,

    You are talking about isolation transformers right ? I read about them, I will inform myself a bit more.

    Thing is, I was not expecting that, since everything I could see pointed towards an Earthed chassis and frame : green wire screwed to frame, continuity between GND, frame, etc... so I was extremely surprised to see that 120 everywhere, and to feel that little tingling when touching the plastic case coated with that conductive black paint...

    Curiously enough, I wasn't able to replicate that situation again, after disassembling and reassembling the Osborne several times, it doesn't do that anymore, the GND is clean now, and everywhere the same, and the same GND as my scope ... so I wonder, maybe the earth connector was oxidized, or not properly tightened, not doing it's job for one reason or another, or another wire was not at the correct place ... I don't know, but now, everything is fine.

    Now ... that screen, it's very strange ! It's the second time now that it starts working again, and fails shortly after.
    Each time, same thing, I redo a solder joint here and there, clean the board with alcohol, temporarily plug everything back, and it works:
    IMG_20190812_203532.jpg

    I noticed that one of the trim-pot on the board is really bad, here is a picture of what it does when I barely touch it:
    IMG_20190812_203626.jpg

    I have no idea what is causing it to randomly work. Wiggling the wires makes no difference, so I'm not sure that it's a bad connection. Each time it started working again, I was tinkering with the board, and cleaning it with alcohol. And after installing it properly again, it stops working... So my latest stupid hypothesis : could it be that the alcohol temporarily "resuscitates" a bad component or connection (like a trim-pot ?) ? Have you ever heard of or observed something like that ? I'm out of ideas ...

    And I still can't begin to fix my boot error because of that

  8. #8
    Join Date
    Jul 2019
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    Montréal, QC
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    ok ! I re-did all the solder joints from all the wires and connectors on the board, and now it seems to be working fine, and reliably. So it looks like it really was a bad solder joint after all. As for the trim-pots, next time I won't use a metallic screw-driver ! When using non conductive screw-driver, they work perfectly...

    So now, finally, back to my boot error

  9. #9
    Join Date
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    Quote Originally Posted by Yakeru View Post
    I entirely re-caped the machine, (PSU, MB, Screen, Floppies, ...) It might be overkill, but before doing that, the screen stopped working, and my vintage audio-amp started showing signs of needing a re-cap, so why not ...

    Now it's re-caped, and it won't hurt. But no improvements. The screen issue seems to be intermittent, it started working again while I was probing with my scope, and stopped working shortly after again.
    As for the boot error, still there, even with a set of freshly made and tested floppies.

    One question to you hardware gurus, might be a stupid question, but I know only the very basics : is the ground supposed to be live by design in that machine ?

    By default, when the components are layed flat on my table, everywhere I probe with the scope, I see 120V 60 Hz.
    If I clip the ground alligator of my scope to the ground of the logic board, or frame, it shorts (logical... if the ground is live, and my scope clip goes to earth...).
    If beforehand I connect the frame and ground of the board to Earth, then I get the correct readings on my scope, and since the clip of my scope and frame are now both the "same ground/earth" I can clip anywhere, it doesn't short anymore, actually, I don't need the clip, since it's the same ref.
    In both cases, live ground, or earth ground, the machine seems to work the same, that's what bothers me...

    Ground can be anything you want it to be, but live 120 ? And works the same whether it's live or earth ? There must be something very basic that I don't know or understand, or something very wrong with the PSU

    Thanks for your help
    Most PSUs have an input filter that bypass RF to ground at the AC input. The Osborne is no exception. I'm assuming that your 3-wire plug has a good ground.

    You're probably seeing some bypass leakage, which shouldn't be problem, as it's probably in the microampere range. If you're unsure, a small wattage (say 10-20W) lamp connected between signal ground and AC ground will quickly point out ground faults.

  10. #10
    Join Date
    Jul 2019
    Location
    Montréal, QC
    Posts
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    Default

    Thanks ! I replaced the filter cap as well, maybe that's why I don't see the 120 anymore then.

    As for my screen problem, this topics describes exactly the same issue I have ! Including the temporary resuscitation with alcohol/contact cleaner !! awesome !! http://www.vcfed.org/forum/showthrea...ve-CRT-problem

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