• Modular C64 replica

    From Niels Haedecke@21:1/168 to All on Wed Feb 28 19:37:17 2024
    I've been asked about that Commodore 64 replica I have built and here
    is some information about it. I've just checked and the vendor I bought
    the PCBs from does no longer sell the model I have but a much more
    expensive version which is a gold plated, "limited edition" that is
    a new revision of the model I built.

    So the thing is commonly known as "Modular 64" while the model description
    of my kit officially was "uAX64 Mini Long". "Long" means 9 module slots
    while the "uAX64 Mini" only featured module slots.

    So imagine a Commodore 64 that looks like a RC2014 (if you know that one):
    each component of the computer (RAM, ROM, CPU, I/O) is placed on a
    seperate "module" PCB that slots into a 72 connector card slot on a 9
    slot backplane.

    Here are the individual modules:

    The VIC II chip has its own module with a composite and an S-VHS output.

    The SID chips (two of them) have their own module. Each SID socket has
    optional jumper settings for 6582 or 8580 chips and for the latter, a
    "digi fix" filter can be selected via a jumper.

    The two CIA (love the name) chips also shre a module, this also has a connector for the Commodore 64 keyboard.

    The PLA (251715, the 64 pin one) and the RAM chips share a module

    and last but not least there's the CPU and ROM module which contains the
    8500 CPU and the Kernal and Character ROMs.

    Oh and there is a bluetooth interface module that allows a special
    software (mobile app) to use your mobile device as a remote keyboard.
    But I rarely use it.

    Now, since you only get the PCBs and (if you like) the passive parts like resistors, capacitors, diodes etc. you need to find the required custom
    chips. If you are a sensitive person, you probably shouldn't read the
    next paragraph as it may contain disturbing passages. You have been warned!

    Luckily I was in possesion of a working C64 C motherboard. All I needed was
    a vacuum desoldering station - which I got myself rather quick (Toolcraft).
    And on the day that suck-o-matic thingy arrived, I desoldered my first ever chip: a 6526 (I did try my luck on the joystick ports first, both came off
    like I was using a charm). So long story short yes: I did sacrifice a
    working Commodore 64 mainboard to build this replica. I know it's a sac-
    rilege and I apologize. The board arrived decades ago with another machine
    I salvaged off some friend.

    So after that job was done, I needed to source a few more parts like voltage regulators and a 72 line ribbon cable. Getting these parts and soldering
    all the components, IC sockets took me about two months. I was very care-
    ful when I built the individual modules and I did take a few breaks
    inbetween as I built this baby in summer 2022 to celebrate the 40th
    anniversary of the Commodore 64 (I also built a Herlequin 128K ZX
    Spectrum replica two months eariler: the Speccy also turned 40 that year -
    yes, I'm absolutely mad ... har har).

    The machine works quite nice, but I had to use tape strips along the
    module connector edges to have a better, tighter fit. Before,
    the machine was a little crash-prone to heavier vibrations.

    The neat thing is that the CIA interface module also has a connector to
    plug a SD2IEC drive in. You know, one of those very small ones.

    As for sound, I am now using an ARMsid and a SwinSID on the sound module but execpt for a few Demos, I don't have any "two-SID" software.

    The Kernal ROM was replaced with a (licensed) version of JiffyDOS so loading times have been optimized.

    Well, that's about all I can tell you about this little machine. You can
    find two photos of it on my Mastodon profile. Link follows at the bottom.

    If you have question, please don't be afraid to ask.

    Link to photos:

    Greetings, Niels Haedecke

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