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Thread: IBM PCjr but really IBM JX ROM burning question

  1. #11
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    Quote Originally Posted by eeguru View Post
    Photos of my busted front panel JX:

    https://www.retrotronics.org/2020/05...anese-version/

    I recall seeing Kanji when I last powered it on. Can a Japanese version be converted to an Australian/NZ version with a ROM swap-out? (main and character?)
    I've never tried it, but I'd say that's quite likely. Ours were the same motherboard, just with things removed.
    Only things I wouldn't be sure of would be if you need to also remove the second 1mbit ROM (I imagine you dont), and if the english ROM is compatible with the EXVIDEO card (although you can just unplug that).

    One question while we're here, what are the other chips on that EXVIDEO card? In adverts I've seen IBM Japan advertise "VRAM" seperately and wondered if any of the chips on the EXVIDEO cards were RAM or just logic.

  2. #12

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    Quote Originally Posted by Anthony Beckett View Post
    Looking at some photos online, the PCjr does not appear to have socketed ROMs like the JX does - which is interesting and may be a problem for this discussion.
    FWIW my PCjr has socketed ROMs. Looks factory, I don't see any signs of re-work on the board in that area.

  3. #13
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    Quote Originally Posted by Anthony Beckett View Post
    But there isn't a technical reference guide (that I have seen!) for the IBM JX.
    Courtesy of ibmfan22 on Mike's forums:

    JX Technical Reference

    JX Logic Drawings

    Indeed the system ROM is 128KB in a 28-pin DIP package.
    "Good engineers keep thick authoritative books on their shelf. Not for their own reference, but to throw at people who ask stupid questions; hoping a small fragment of knowledge will osmotically transfer with each cranial impact." - Me

  4. #14
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    Quote Originally Posted by eeguru View Post
    Courtesy of ibmfan22 on Mike's forums:

    JX Technical Reference

    JX Logic Drawings

    Indeed the system ROM is 128KB in a 28-pin DIP package.
    Wow.
    I did not think these existed!

  5. #15

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    The font rom of JX Japanese seems to be from P/N : 6342628~6342631.
    It can be dumped from EPROM Reader or binary program I attached.

    https://2.bp.blogspot.com/-gJ8bxYMqR.../cDSC_5807.jpg

  6. #16
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    Wow. I just got these emailed to me from Aram - I am wondering if this is where these came from? Thanks very much - I have not seen the logic drawings.

    Anthony

  7. #17
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    Quote Originally Posted by Anthony Beckett View Post
    Wow. I just got these emailed to me from Aram - I am wondering if this is where these came from? Thanks very much - I have not seen the logic drawings.

    Anthony
    They came from Aram. But re-OCRd them in Acrobat and moved the quality/size slider more than a little bit. 160 MB to 12 and still look ok.
    "Good engineers keep thick authoritative books on their shelf. Not for their own reference, but to throw at people who ask stupid questions; hoping a small fragment of knowledge will osmotically transfer with each cranial impact." - Me

  8. #18
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    Quote Originally Posted by eeguru View Post
    Photos of my busted front panel JX:

    https://www.retrotronics.org/2020/05...anese-version/

    I recall seeing Kanji when I last powered it on. Can a Japanese version be converted to an Australian/NZ version with a ROM swap-out? (main and character?)
    The Australian JX does not have sockets where the Kanji ROM is - I am guessing you can - this is what I am trying to test with Aram and why I am trying to burn him a ROM. I have about 10 Australian JX units with all manner of accessories, but I have zero Japanese JX units. I'm going to have another trial of reading the ROM with my EEPROM burner, hoping to see what I can get.

    Aram could not get any of the disks working on my website, which seems to indicate there is a compatibility issue with PCjr/AUJX and JPJX OR his drives are dead. For the record, standard 1.44MB floppy drives DO work in a JX and read in 720k format should your drive be dead.

    Anthony

  9. #19
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    Alright. I have used Mikes PCJRCART program to download the ROM from my most up to date JX.

    I am either incompetent or do not know how to read the ROM using my EEPROM reader as it does not associate a 28 PIN DIP with a 128k (1MB) ROM.

    SO - Should I want to get this ROM to Aram or whoever, how would I assemble the contents in a package on a ROM, considering there is 100k of data here. Mikes program shows the addressing in memory, but how would this be laid out for a single ROM?

    Alternatively, is there an adaptor I can get or some other software that can make my TL866-II Plus read it to save me the headache?

    I'm sorry to ask these questions, but I have a bit of a knowledge gap here.

    Thanks;

    Anthony
    Attached Files Attached Files

  10. #20
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    Quote Originally Posted by Anthony Beckett View Post
    I am either incompetent or do not know how to read the ROM using my EEPROM reader as it does not associate a 28 PIN DIP with a 128k (1MB) ROM.
    The 128Kb 32-pin eprom equivalent to a 28-pin mask rom is HITACHI 27c301 (or ST 27c1000)

    Your programmer "should" support this eprom type.

    Unfortunately, there is catch...

    On the 28-pin mask rom you are trying to read , VCC (5V) is on pin 28 .
    On a 32-pin eprom (like the 27c301), the VCC is pin 32.

    So if you try to read the 28-pin mask rom as a 27c301 eprom, you are not getting the VCC to the correct pin.

    What you would need to do is make a small jumper/wire connection on your programmer's ZIF socket.

    A 28 pin chip has 14 pins on each side, and a 32 pin eprom has 16 pins (...well duh !),
    so on the right side of the ZIF socket, just put a small wire from pin/slot 16 to pin 14
    (... which is equivalent to pin 32 to pin 28 on the chip).

    So here is what you do :
    1- Select Hitachi 27c301 eprom type on your programmer
    2- Put your 28-pin mask eprom on the programmer
    3- Put a small jumper wire from pin/slot 16 (on the right side of the ZIF socket) to pin 14 (which should be the top corner pin of your mask rom).
    (this should provide VCC to pin 28 of you mask rom )
    4- Read the eprom

    You "should" get a 128kbyte image from this.

    If you can view the contents, I would assume you should find some readable text stringa.
    This would show that you got valid data.

    Let me know if you have any questions.

    Cheers,
    Steph

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