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Thread: Ibm pc jx

  1. #1
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    Default Ibm pc jx

    Yes JX, not JR, I didn't make a typo
    Thought I'd share it with you guys who haven't heard me rambling on in #vc on slashnet already.

    So here it is, in amazingly good condition (I purchased it site unseen, and another collector picked it up and shipped it for me)



    The first thing I noticed with this was the keyboard - this is the full keyboard with numeric keypad and the typing feel is fantastic. Like the JR it is also wireless, using 4 x AA batteries but does have a cord option.



    Internal expansion was fairly poor. I guess to discourage people from using it as a business replacement to the IBM PC 5150/5160 desktop units - they removed the JR's sidecar system and only provided minimal internal slots.



    There are three slots. Top left is an RS232 card, and below it is a 64KB RAM card - the slot it's in appears to be only for use with a 64KB RAM card and is marked "EXRAM64". The card on the right is in the EXRAM128 slot - and provides 256KB of memory (these cards were available in 128,256 and 384) and judging by the battery also provides the user with a real time clock. So with the 64KB built in - we've got 384KB of RAM and a serial port - and now the only upgrade options we can add on is a 5.25" floppy drive top-hat or a 10MB ($NZD1700+ btw) hard drive top hat.



    So not much expansion to be had. We did however get to keep the JR's graphics modes (plus a few more) and sound.



    In fact that part of the system is so familiar, that "JX ColorPaint" and the built in MS BASIC - still think it's a JR


    It is also well known the original BIOS only understands 40 track drives, despite the machine coming with 80 track drives. A later BIOS upgrade with DOS 3.2 magically unlocked the 720KB ability.

    Now with that in mind, you may be wondering where my disk drives are. Sadly this was the base model - so no floppy drive module - which also means it's missing the internal attachments. The owner did upgrade it to be 384KB - but never seemed to get around to the disk drive upgrade.

    This makes me wonder why the owner chose the JX over a Commodore, Apple, or even Amstrad system. It may have a bit more processor power but ultimately it was a BASIC system.

    Pricelists (in what I beleive is NZ Dollars) - take note of the little message written in pen - I suspect this is why it does not have floppy drives fitted.


    Some things you may have noticed:

    - having more than 64KB of RAM would be useless with MS BASIC
    - it has the PC DOS Tech Ref
    - yet it has no drives?

    I think nobody told him about how useful the memory would be in BASIC, and documentation shows he requested that IBM send him the tech ref - perhaps to check what it does before investing in the floppy system. Instead of upgrading it, the user (other docs/gear provided) purchased an IBM Model 30. The front blanking plate looks original, and with everything being so prestine, I am fairly sure the configuration is likely "as it was" in the late 80's.



    Right now I'm very very keen to find a floppy module for it!
    Last edited by SpidersWeb; March 22nd, 2015 at 01:07 AM.
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  2. #2

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    Wow, I've been waiting for ages to see another JX machine!.

    Mine is fully expanded with memory maxed (768KB IIRC) and two floppy drives; but the keyboard stopped working!, do you have the keyboard cord or any info about its pinout?, I'm trying to build one and try to debug my keyboard.
    Also, I didn't know the existence of a BIOS update , if I'm able to repair the keyboard, I'll check this.

    If you need some info about the drive controller I can take some pics...

  3. #3
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    768KB wow, was it modified or does it have an aftermarket card in it?

    I'm not sure of the pin out sorry, you could probably use a voltmeter/oscilliscope to work it out what pins were what fairly quick (+5 GND CLK SERIAL RESET etc) (or open the keyboard and trace the wires) but I wouldn't know anything about the protocol etc - I'd expect it's likely quite close to the PCjr though, and I wouldn't be surprised if a JR keyboard worked on it.

    I know what the FDC module looks like, but if I get desperate enough to make my own I might PM you to get photos of both sides of the board I do have some questions for collectors though:

    - does the 5.25 expansion module have it's own FDC inside? Or does it operate as Drive 3 off the 3.5" module?
    - how does the 10MB expansion unit connect internally?
    - what's the difference between a 256KB Card and a 256KB Cluster Card? (my 256KB card has a battery on it - RTC possibly)
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  4. #4

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    Holy shit!, things are getting messy in my head!. I've just tested the machine and it clearly shows only 384KB

    It has three boards, the aforementioned EXRAM64, the long card with 256KB and a thrid one, named "EXVIDEO" with 32KB RAM chips, probably used in some extra video modes...

    I can try with the Jr cord; but I'll need to check first where're located the voltages and ground, I don't want to fry anything.
    Severe battery leakage badly corroded the inside of the keyboard and I'm afraid that there're broken tracks.

  5. #5
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    Yeah the 32KB expansion lets you do some of the higher resolution modes. I don't think much English based software made use of this, but I'm sure some of the Japanese stuff did. Apparently there was startup cartridges that let you boot the machine in the higher resolution text mode.

    Where does the EXVIDEO card go? Does it replace the serial port?

    I'm not sure if the standard JR cord would work, but I was thinking it may work over infared or with a cable adapter made up. I can't remember what the peanut's plug looks like.
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  6. #6

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    I've taken a pic:



    The EXVIDEO card goes in the leftmost (in the pic) slot.

    Damn, I've checked the plugs and forgot that the JX has a 6 pin miniDIN type (and I don't have the slightest idea of the pinout). The Jr uses a 5 pin Berg type plug. I can blindly try the infrared protocol; but I doubt that they shared it

  7. #7
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    hmm that's interesting, your power supply is slightly slimmer, and you have that extra slot. In mine (and the other motherboard photos I found on the web) the power supply sticks out a bit and you can just barely see the solder points where a card could be installed. If you've got that video extension, I wonder if you have the Kanji ROM too (its under the disk drives, I just have solder points with the writing "KANJIROM").

    Thanks for the photo, one other question I had was to do with power but I can see in your photo (missing from my other source) there is a power link between the FDC and PSU.
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  8. #8
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    It seems like there are four slots, judging by that picture. One for the EXVIDEO, one for the Serial adapter, one for the EXRAM64, one for the EXRAM128.
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  9. #9
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    Quote Originally Posted by Great Hierophant View Post
    It seems like there are four slots, judging by that picture. One for the EXVIDEO, one for the Serial adapter, one for the EXRAM64, one for the EXRAM128.
    Only if you bought a model that had an EXVIDEO slot I don't have it. Even if it was soldered in, my power supply wouldn't clear another card there.
    I'm wondering if that slot was only available on the Japan 100V units, or in higher end models. I'm not sure what model jltursan has.

    If anyone has a broken JX and wouldn't mind selling their drives for $$$ let me know. Quite badly want to make this thing useful again.
    Last edited by SpidersWeb; March 22nd, 2015 at 09:18 PM.
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  10. #10
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    Quote Originally Posted by SpidersWeb View Post
    If anyone has a broken JX and wouldn't mind selling their drives for $$$ let me know. Quite badly want to make this thing useful again.
    FWIW (NOT mine!): http://www.ebay.com/itm/VINTAGE-IBM-...item487c3264de

    Mike

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