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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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Boffin

Your B8229...

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

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and 8218...

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

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8226 and 8229

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

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Headmaster

You must be ancient like me...

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

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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....

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Silver badge

Looks like the horzontal deflection of the crt is shot

Could be fixed but might not be economical ;-)

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Boffin

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.

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Boffin

Yeah, interesting, but ...

... will it blend?

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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.

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Are you sure?

No chance that's a Fairchild chip?

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Nice teardown

The MM5290 datasheet can be found here: http://www.alldatasheet.com/datasheet-pdf/pdf/148600/NSC/MM5290.html

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.

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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

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Silver badge

I assume

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

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Dual Floppies...

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

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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.

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Pint

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

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Cooling fan

The 11" MacBook Air does have a cooling fan:

http://www.ifixit.com/Teardown/MacBook-Air-11-Inch-Model-A1370-Teardown/3745/1

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Boffin

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!

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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.

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Go

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.

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@RayG

"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?

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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

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@Annahilator

No scar on finger but one my head.

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

Ouch

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caps

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.

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Joke

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...

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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.

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well,

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.....

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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.

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Silver badge

Dual Floppies

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

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Silver badge

That calendar on the keyboard...

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

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Jobs Halo

Lack of cooling fan...

erm the Macbook Air does have a fan.

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If you can find a TTL monitor...

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

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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...

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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. ;)

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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:

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Boffin

Unknown B8229 DRAM chip

You've got 16Kbits of this:

http://www.alldatasheet.com/view.jsp?Searchword=5290N-2

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Sockets

What are the sockets under the floppy drives?

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Anonymous Coward

ahh...

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

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Happy

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?

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Happy

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.

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Happy

Wow.

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. :)

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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!

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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).

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Boffin

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.

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Unhappy

Oops

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.

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Alert

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!

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Bronze badge

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

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Coat

Untrue

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.

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Happy

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.

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meh

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

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