back to article Naked at 30: Osborne 1 stripped to its chips

The Osborne 1 – the first mass-market portable computer – turns 30 years old this month. And what better way to celebrate than by tearing one apart? One problem: I couldn't get my hands on an original Osborne 1. But I was able to tear into the next best thing: the slightly remodeled follow-on to the original, also known as the …


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  1. Michael Jarve

    Your B8229...

    Your mystery B8229 chips are National Semiconductor MM529 16Kb DRAM chips.

    1. Wanda Lust

      and 8218...

      are AMD's equivalent AM9016 16k x 1 DRAM chips. The 82xx numbers are the manufacturing date codes, year, week.

    2. Borg.King

      8226 and 8229

      These are likely the manufacture dates for those chips, 1982 week 26 and 1982 week 29.

      1. unitron

        You must be ancient like me...

        Good to see someone here can properly read IC date codes.

  2. cjcox

    Fond memories

    Owned the Rev A myself. And did have the external monitor as well as the 300 baud Osborne pulse dialing modem that fit into the floppy holder slot by the port. The Rev A had double density single sided drives where the original had single density. So everyone cut the notch in their floppies so we could turn them over and use the backside. My Osborne I ran: Turbo Pascal, COBOL, LISP, C, Z80 Macro Assembler in addition to the normal package and the plethora of add ons through the many BBS CP/M sites. At school, armed with a 300 baud modem, I did my mainframe work via Wordstar and uploaded it to save valuable "dollar" allotments on the school's mainframe. I was the envy of my dorm since 128 scrollable display is good enough to display the majority of mainframe output which was formatted for a maximum 132 character line printer. I made my own modifications to OSWYLBUR to handle the strange Osborne I modem... and many of us replace the CP/M shell with ZCPR, a command replacement with more features. I even hacked in a pulse dialing modem routine in place of the built in DIR command, since most people used a directory listing program from disk instead. I also programmed a game using the Software Toolworks C compiler where you flew around the screen and turned asterisks into boxes. The asterisks would kill you if you ran into them and the boxes were like walls, so as you played your ability to move about the screen decreased. What fun! I also wrote a mainframe 370 assembler in macro Z80 assembler. This allowed me to do a lot of my labs without using valuable compute time... just had to upload the final product. In high school, I developed a text adventure game (ala Infocom) where you had to solve chemistry problems to get through obstacles. In my junior year of college I wrote a small BBS in assembler for my Technical Writing class.

    Great machine... I wish I had never given it away. It was very useful. It was fun keeping my dorm mates up all night as they listen to my TTX 1014 daisy wheel printer typing away....

  3. Michael H.F. Wilkinson

    Looks like the horzontal deflection of the crt is shot

    Could be fixed but might not be economical ;-)

    1. unitron

      But horizontal section seems to be working

      In order to get the screen to light up at all, the horizontal section needs to be working to generate the kilovolt(s) needed to attract the electron beam from the cathode to the front of the tube to hit the phosphor, so it could be that the horizontal oscillator and the driver transisitor and flyback and damper are all working, but the horizontal deflection coil(s) is(are) open or one end has come disconnected due to a bad solder joint.

      Unless for some reason they did everything backwards and the vertical deflection section is the one that generates the high voltage for the CRT, in which case you just rotate the whole thing 90 degrees and troubleshoot like an ordinary loss of vertical deflection.

  4. Ralph B

    Yeah, interesting, but ...

    ... will it blend?

  5. Neil Barnes Silver badge
    Thumb Up

    I'm feeling my age now...

    I've used half those chips in my own designs, back in the day... yes, the M8877 is a Fujitsu floppy controller.

    If you feel the urge to fiddle, replace the line driver transistor in the monitor - it'll probably be a TO3 package, maybe on a heat sink, close to the line output transformer. There's a good chance it will all then work; old TTL electronics are a lot tougher than you think.

    1. unitron

      Are you sure?

      No chance that's a Fairchild chip?

  6. MondoMan
    Thumb Up

    Nice teardown

    The MM5290 datasheet can be found here:

    Brings back fond memories of doing so many assembler runs on my IBM PC's floppies that the disks wore out! After a while, we only bought Verbatims, since they lasted the longest.

  7. James Holt

    dual floppie

    funny that it comes with dual floppies given it's supposed to be portable. I suppose this is pre-the days of Apple's less-is-more thinking

    1. LaeMing

      I assume

      you would run your application from floppy A and store your data on B

    2. JimC

      Dual Floppies...

      One for the Application, one for the data...

    3. saundby

      Two floppies req'd

      It took two floppies to be useful, especially with single density drives. One had the program & its overlays, the other your data disk.

      As it was there was software that wouldn't fit because it expected the greater capacity of the IBM-format 8" disks. When double-density became common, it helped, but it wasn't until quad density came along (not to be confused with high density 1.2MB diskettes) that mini-floppies had the same space available.

      1. Darryl

        Dual floppies rocked

        Never played much with CP/M, but I remember the bad old days of only having one floppy in DOS:

        Insert disc in Drive A: to continue...

        Insert disc in Drive B: to continue...

        Insert disc in Drive A: to continue...

        Insert disc in Drive B: to continue...

        Insert disc in Drive A: to continue...

        Insert disc in Drive B: to continue...

        Insert disc in Drive A: to continue...

        Insert disc in Drive B: to continue...

        Ah, memories

  8. edward wright

    Cooling fan

    The 11" MacBook Air does have a cooling fan:

  9. edward wright

    Logic chips near the RAM

    It's the 74LS** chip numbers you should be looking at.

    The K8241 = 74LS00 contains four 2-input NAND gates.

    The K8243 = 74LS04 contains six inverters (NOT gates).

    These are 5V TTL (transister transistor logic) lower-power Schottky chips. I used to play with them as a kid. Happy days, when some chips contained < 100 transistors!

  10. petur
    Thumb Up

    RE: horizontal deflection

    back in the days when I did some field service work, 9 out of 10 times this horizontal deflection issue (vertical line in the middle) was just a solder joint gone bad. 5 minutes work to fix...

    Inspect the solder points of the video board and look for fine circular cracks or lines on the solder.

    1. RayG

      Definitely worth trying to fix

      Absolutely right about the solder joint; but from my very limited experience of iffy CRTs, the next things to check are resistors and capacitors - all cheap, thank goodness! - before you need to start worrying about anything complex or difficult.

      Just make damn sure the caps are empty before you start work.

      1. Annihilator


        "Just make damn sure the caps are empty before you start work."

        You make that mistake exactly once and only once... Anyone else got a tiny scar on one of their fingers where they accidentally brushed a fully loaded cap?

        1. Anonymous Coward
          Anonymous Coward

          No but

          I have seen someone go flying when they accidentally toutched the wrong side of a flyback transformer. Well named that.

          Landed on his arm and broke it.

          There isnt much actual power in there, but there is enough voltage to cause a small current flow, and it doent take much of a current flow near a nerve to cause the attached muscles to contract violently

          1. Alan W. Rateliff, II
            Paris Hilton

            That damned flyback transformer

            Yup. Yup. Many moons ago I found a rather large color TV at a garage sale. I was told it worked, kind of, and I traded $5 of my hard-earned paper route money for it. Walked it home on my bike and immediate set to work on it.

            I saw several cold solder joints and began screw driver surgery to reach them. The long-shank driver brushed across the terminals of the transformer or one of its compatriot capacitors -- it is all a bit fuzzy at that point -- and my arm shot right up into the air, my hand releasing the screw driver which became embedded about a half-inch into my bedroom ceiling.

            Lesson well learned that day.

            Paris, heed the stickers.

        2. zebthecat


          No scar on finger but one my head.

          Catapaulted accross my bedroom after touching the smoothing capacitor in my home made bass power amp.


          1. gzuckier

            not to mention the time

            that i discovered the hard way that a previous tenant of my apartment had for some ungodly reason wired the metal chassis of the over-the-kitchen-sink light fixture to the hot wire, after disconnecting the shield of the bx cable from the clamp.

        3. gzuckier


          there was the time at the science fair when i absent mindedly grabbed the leads to the aluminum foil and glass capacitor the guy built for his Tesla coil.....

    2. easyk


      I made that mistake twice myself but it was on the same day. I was examining a power supply with a really big al-elec 200V cap. It discharged on me. After I picked myself up I made the stupid assumption that now that it had kicked my ass it must be fully discharged. It wasn't.

      1. Anonymous Coward

        fun and games...

        when I was at collage doing a HND in electronics and radio engineering we used to get some 4.7kuF caps,,, charge them up and play catch with them... we all use to put a quid in a hat and the last one 7standing took all...

  11. Mage Silver badge

    Dual Floppies

    You used one for OS & Application and the other for data.

  12. Uncle Slacky Silver badge

    That calendar on the keyboard...

    ...looks like week number (of whatever the current month was) on the vertical axis.

  13. Anonymous Coward
    Jobs Halo

    Lack of cooling fan...

    erm the Macbook Air does have a fan.

  14. Peter Gordon

    If you can find a TTL monitor...

    ... hook it up. The computer might still work.

    1. Alan W. Rateliff, II
      Paris Hilton

      Find some old Commodore monitors

      2002, 1084, etc... these are all TLL-capable. Just need to work the pin-out. Matter of fact, a PCjr monitor will probably work as well; I made an adapter to connect my Commodore 128's TTL output to a PCjr monitor. Found it in storage recently...

      Paris, ah, yes, memories, indeed...

  15. saundby
    Thumb Up

    Still Using Mine

    I got one this last year that I'm using, along with an Ampro, Big Board, and Kaypro IV. The Ampro and Osborne are my favorites.

    I mostly write code in assembly and Turbo Pascal.

    I also use mine as a luggable. For a week I take it into the computer classes I teach to demonstrate some visible computer hardware for my students. It's not an Eee PC 900 by any means (my usual portable), but it does travel very well in spite of its weight. The students _love_ floppy drives (and Zork).

    Good writeup!

    Your mystery chips have the date code on top, designation on the bottom. You've got National Semi MM5290N-2 memory chips produced in the 29th week of 1982. Be sure to list them as *****RARE***** on ebay. ;)

  16. Just Thinking

    You guys have good memories

    One of my first jobs, in the early eighties, was programming something which was probably one of these (it was a CPM machine in a very similar case, with the detachable keyboard).

    I don't have the remotest recollection what the project was ... completely erased from my memory :( Scary.

    @James Holt - two floppies because it didn't have a hard drive (I think). Compiler disk in A:, source code disk in B:

  17. edward wright

    Unknown B8229 DRAM chip

    You've got 16Kbits of this:

  18. Liam Johnson


    What are the sockets under the floppy drives?

  19. Anonymous Coward
    Anonymous Coward


    ...that must be the Green Line Of Death. Never laid my hands on an Osborne though.

  20. Andy The Hat Silver badge

    Surely no problem ... #2

    Osbourne 1 was the first computer I seriously 'networked' using RS232 and lovely CP/M whilst at university ... there was an os that people understood and it did what it was told! Imagine routinely hacking os code nowadays (using info from something they called 'the manual') without breaking at least three layers of MS system rubbish ... I still remember the geeky amusement of the Spitting Image 'RS232 interface lead' song as we kermitted stuff about :-) Two drives were amazingly helpful otherwise disk swapping with a pile of half a dozen floppies became a nightmare.

    We had a Kaypro ll as a Wordstar engine for a while ... worked fine but somehow never had quite the same impact as the Osbourne ... perhaps some of the teenage geekiness had worn off by then?

  21. Adrian Challinor

    I remember this...

    We had one as a very early network analysis tool, because it was "portable". I recall carrying down The Strand one day, and realised that a handle does not make something portable! I swear one arm is several inches longer than the other still.

  22. BorkedAgain


    I remember cutting notches in "single-sided" floppies so that we could use the "B" side - always worked just fine. Liked the look of the Osborne, but cut my teeth on the TRS-80. There's something about a big, round "Reset" button with a mechanical "click" that makes me grin. :)

    1. Steve Evans

      Re: Wow...

      Oh blimee, me too... It used to be easy on the later commodores, just cut a new read only notch and flip it over. The BBC micro was not so easy, the beeb actually used the optical rotation index hole, so you had to make another one of those two... Which involved extracting the floppy bit, chopping the hole and then feeding the floppy bit back in.

      Always seemed to get away with it though!

  23. A J Stiles
    Thumb Up

    You've lost horizontal deflection

    Probably an easy fix. A dry joint on the line output transformer can kill its drive transistor (and, if you are very unlucky, the transformer itself).

    Re-solder all the joints on the Line Output Transformer (thing with the ferrite core and a HT cable coming out of it). Replace the big transistor next to it (Probably a BU208. Don't bother testing it. There may well be an internal resistance across B-E which will spoil your test results, it's probably about had it anyway and besides which, they are cheap).

    1. Hairy Scary

      It's Easy To Fix

      Because, as you have a vertical line, you must have EHT for the CRT which comes from the line output transformer. This means the line output stage is working, its just the line scan coils that are disconnected, that will almost certainly be a dry joint on the PCB where the scan yoke leads connect or possibly at the scan coupling capacitor or line linearity coil. It can't really be much else other than an o/c scan coupling capacitor.

      How do I know this? well, the college I worked for had lots of Osbornes and I used to repair them when they broke down. Most common fault was the extension card for the double density floppies working loose (these things were carried between rooms regularly which probably explains that), next was the display which could fail to work due to dry joints at the line output transistor connections or by the vertical line due to joints as described earlier.

      Once I had to make a new system rom for one (by copying a good one from another machine) as the suspect one was partly corrupt (would boot to the Osborne startup screen but would intermittantly fail to load the o/s from disk) -- that took a while to diagnose.

      One other task I had to do was calibrate all the floppy drives so that disks were interchangeable between all machines -- there were quite a few that would not reliably read disks from other machines until this was done.

      Most of our Osbornes worked with external monitors (to ease eyestrain on the students).

      When carrying machines between rooms I always carried two at a time, that way both arms stretched by the same amount :-) happy days indeed.

      1. A J Stiles


        Oops, my bad. You're right, of course; if the LOPT were at fault, there would be no EHT and hence no green line .....

        In my defence, it's a good while since I was extending my meagre student grant by fixing tellies.

  24. Annihilator

    When floppies were floppy

    "If you've been around personal computers for a few decades, you'll remember when floppy disks were, well, floppy."

    The really scary thing is, anyone who's born in the last 15-20 years will probably not even know what a floppy disk is/was, let alone whether it was truly floppy or not!

    1. pepper

      not quite

      22 years old, and I grew up on floppy disks. Although that was probably because we always got the old equipment from other people instead of buying it all new ourselves. I even grew up gaming on a commodore 64 in the mid nineties. I still have it and will cherish that machine to death.

      I know, I fall out of the age range with 2 years

    2. bkcokota


      I'm 20 and I used to use the terminals which managed the library system at primary school, the program was on 2 5 and a halves and were a nightmare to get working because the discs kept failing due to their age (they didn't even want to shell out for new disks). From what I know they haven't upgraded their systems yet... I also remember installing Fifa 95? (not so sure about the year) on the computers running 98SE we had there, Good memories.

  25. hugo tyson

    Floppy drive speed

    Also, like "proper"[1] turntables for vinyl, love the speed check strobe markings - for both 50Hz and 60Hz incandescent lighting - on the pulley of the floppy drive. When it was worth repairing such a thing!

    [1]ie. wannabes.

  26. Sandy Ritchie


    Looks like it could be fixed if someone checked for dry joints on the CRT board.

  27. Anonymous Coward

    "...even though I'm not in the least bit an EE kinda guy..."

    Shame, I prefer my hardware teardowns to be written by at least *slightly* EE kinda people...

    But then, as Mr Page has amply demonstrated, you don't really have to know what you're talking about to get published by El Reg :-)

  28. Loyal Commenter Silver badge

    I still remember the one of these my dad had...

    ...which was the original model in the tan and black case

    If I remember rightly, it experienced the same 'green line of death', but he could carry on using it with the external orange-screen monitor he had. he finally ditched it when one of the floppy drives gave up the ghost.

    I later furtively opened the thing up and tried to get the other driove working on the Amstrad CPC 464 we had. Apparently the edge-connector on this, although being the right size and shape, had some of the pins swapped, so I never got it to work. I would have been about twelve at the time, so I get the points for trying anyway!

    Seeing the insides of one of these again after so many years brings back fond memories. I wonder whatever happened to the one my dad had...

    And @CJCox above; I too remember the shrill cacophony produced by daisy-wheel printers, which I think can best be described as someone dragging a hessian sack full of broken china back and forward across some iron railings.

  29. Inachu

    I miss my c-64

    I saw a c-64 that looked a lot like this Osbourne 1.

    I'll have to google and see if I can buy one.

    1. Steve the Cynic

      Commodore SX-64...

      Yes, Commodore did a version of the C-64 in an Osborne-style case, called the SX-64. Like the Osborne, it had a 5-inch screen, although the Commodore's did colour. With one exception, I remember mine fondly, in a sad, geeky way.

      The exception was the handle. The SX-64 was clearly designed to *look* portable, but it was also clearly designed in such a way as to discourage you from carrying it. The cylindrical full-width handle was decorated by a series of length-wise grooves that combined with the unit's considerable weight to leave grooves in your hand, and carrying it any distance was actually painful. Bah.

  30. Leona A

    The really amazing fact was....

    ...that the OS fitted on a single density 5.25 inch disk! What happened? Oh ya M$ happened, now you need >1Tb disk just to get started.

  31. The Unexpected Bill

    Couple of thoughts...

    First of all, thanks for an interesting article and exploration. Some years back, I rescued an Osborne 1 from "Curbside Discount" along with a bunch of software. Apart from a burnt out bulb in the power button, it worked quite well. I certainly did not go as far as you did in taking it apart, mainly out of fear of breaking it.

    If you can find a copy of Peter A. McWilliams' Personal Computer In Business book, it will be an interesting trip down memory lane...and I thoroughly enjoyed reading it. Mr. McWilliams was none too fond of the Osborne 1 and made that perfectly clear. He felt the screen was too small, the fan too loud (of which more later) and the character font unclear. His description of the screen's phosphor color was also not to be missed--"several shades of orange, not unlike a punk rocker's hair" IIRC. He also disagreed with Adam Osborne about screen size--Peter's thought being that bigger screens were the way of the future while Adam insisted that smaller screens would be all you'd see. In their own ways, I think both men were right.

    (If anyone out there still has the supplement to this book that is mentioned at the back--I'd love to know about it. Likewise, I think there was a much later version published in the 1990s that I can't seem to find now.)

    I was surprised to see that your system had what appeared to be a green phosphor display, and found the lack of a cooling fan interesting as well. Every O1 I ever saw had the cooling fan underneath a sliding door in the handle. I don't think there was a black and white version of the display--I definitely did not expect to see a green one!

    As for the display, it's probably fixable. You should turn down the brightness and contrast dials before the screen gets a permanent line or a "belly button" burned into it. I would bet that the failure is either bad solder or dried up capacitors that have drifted far from specifications over the years. Bad solder could be determined by poking at the CRT board with a **well insulated** object. If you're not comfortable around very high voltage electronics, see if you can get a knowledgeable friend to help--and maybe you could owe them a favor or buy them dinner?

    Anyway...that's a pretty cool walkthrough of the system. Thanks again for doing it and sharing the result.

  32. Delboy

    Where it all started

    The Osbourne 1 Rev A was my very first experience of computers. My company presented one to me in 1982, complete with external monitor, and the instruction, "See what you make of that". After that, I graduated to Geek and the rest is history.

  33. Anonymous Coward
    Anonymous Coward

    The BBC B I took delivery of... a series 7 board and is dated 1982. Wow. Technology made quite a jump in even that short space of time back then.

  34. Steven Hunter

    There's one here now

    As I type this we have an Osborne of this vintage on the shelf next to me. We had some people move offices in 2010 and they abandon some equipment when they did so resulting in an Osborne being unceremoniously dumped into the IT area. When we first picked it up it shook and rattled like it was full of loose screws; which is was. Apparently someone had been dropping miscellaneous screws into the heat vents over the last 20 years or so. Popped off the hood, dumped them all out, and was surprised to find that it booted straight up into CP/M on the first go.

  35. Anonymous Coward
    Anonymous Coward

    Fairchild, not Fuji

    The MB8877 chip is probably made by Fairchild, not Fuji.

    1. unitron
      Thumb Up

      Thank you!

      I was sure that was a Fairchild.

      I bookmarked that link so fast the mouse is still smoking.

  36. Don Quioxte

    It is HPIB, not GPIB

    For those Hewlett Packard diehards it was known as the HPIB (Hewlett Packard Interface Bus) long before it was known as GPIB or IEEE-488. And if you call it by its proper name, HPIB, I promise not to tell Simon it was you that scratched his car...oh, about an hour from now.

    1. John 62

      National Instruments, too

      I was still using GPIB in my last job in 2009. The daisy-chaining was cool (although the big-ass cables and connectors were cumbersome), but setting addresses via dip-switches or deep in instrument menus was not so cool. We used NI drivers because HP's didn't work for us.

  37. dingo

    Remembers me of the Philips P2000C

    Back in time we used a Philips P2000C which concept looks like quite similar to this one. Except for the bigger screen and 2 80 track floppies rightsided with an amazing 360 kb if remember correctly. With 80x25 lines, Wordstar,Calcstar and MBASIC it was a quite usefull computer albeit a little hefty to carry. Later on you even could get an MS-DOS co-powerboard and a 10 Mb HDD. Great machine!

  38. Anonymous Coward

    "...even though I'm not in the least bit an EE kinda guy..."

    I nominate Mr Fry to do the next teardown. Even better, the machine should be on at the start of the teardown. It may take a few attempts for him to recognize the value of the off switch.

  39. Shippers

    On that second to last picture... looks like your're about to jab a fork into the electronics.

    That would be fun.

    1. Fluffykins Silver badge

      Fork in electrics

      I've often said that.

  40. Paul 77

    I have one but...

    Unfortunately the screen was damaged - the glass is actually cracked - whilst it was on its way to me.

    Anyone know where I can get a replacement CRT? Or how I can actually hook up an external screen using that edge connector?

    I do know that the computer itself actually worked (and I guess the review who wrote the article can try this too), because I hooked up a terminal to the serial port and used something like:

    stat con:=tty:

    It may not have been *exactly* that command, but it was something similar. Different CP/M boxes called their serial ports by different names.

    Great article though. Please, someone, do one on the RML-380Z - I have a non-working one of those too :-(

    1. unitron

      Danger, Will Robinson!

      If the actual CRT is physically damaged, don't turn that thing back on until it's replaced!

      Very Bad Things could happen!

      After donning protective eyewear and gloves, take a look and see if there's a piece of glass in front of the screen, and if that's what's damaged.

      Better yet, find a TV repair shop with someone who's been in the business for years to check it out.

  41. Duffaboy
    Jobs Halo

    I have the following

    I own a osborne 1, Service Manual, Software and External VDU. Sadly I ditched the printer that came with it but this was a star. It was used in my Father in laws business. I also own a signed copy of Hypergrowth by Adam Osborne. The Power supply in this pc/laptop was an Astec which was very common in the mid eightys.

  42. Martin Maloney

    Why do I always have to be the one?

    Real men don't have floppy disks.

  43. Anonymous Coward
    Anonymous Coward

    It's not a logic board

    It's only Apple that call these things "Logic Boards" - to the rest of the world they are Motherboards.

  44. Sven Schubert
    Thumb Up

    Superb article - please keep them coming!

    ... thanks for yet another great article on homecomputer cambrian...

    Even though I now do feel old considering I know DIP switches - I never had the pleasure of owning a Kaypro or Osborne, my portables were rather curious exotics such as the Epson HX20 or the Z88. Although I did own a Sanyo PC XT / 80186 portable, which was following much the same design as the Osborne...

    CP/M wise I was always restricted to the robotron monsters of East German fame, sporting the U880, a Z80A clone. But good times nonetheless. WordStar, SuperCalc, dBII ... not to forget BASIC80 (basi?), TurboPascal, Ladder, Catchum ... and yes, POWER was the handiest piece of software in these days, as a matter of fact, it was so good, I think it wasn't until Norton Commander, that a software tool was such a versatile utility. I mean - come on! multiple file selection through sequential numbers - that was class! ;-)

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