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Thread: Just got a "highly" modded Model I - questions

  1. #1
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    Default Just got a "highly" modded Model I - questions

    The Model I came with a nice EI (with doubler and two power supplies), two Aerocomp drives (as yet untested), and a nice quietly working 5 Meg HD (only two partiions, for some reason).

    The Mod I unit is a 26-1001D with a D motherboard. It works rather flakily (next step is to reseat all the chips) and the keyboard has TERRIBLE bounce (Custom TRS-80, page 99). It does have a lower case mod with descenders.

    Visually, the Mod I has a D9 male connector and two slider switches on the right side (pic 1) and tags on some keys for a strange-to-me program (pic 2, not shown, on the right side of the keyboard the "@" is tagged CONTROL and the "->" is marked Tab). In quick testing, I couldn't find any difference in operation with the switches put in any of the four possible combos. There is also a D9 connector mounted in the same position of the left side of the keyboard, but it is non-functional.





    Opening the unit up, the D9 has six leads going to the keyboard (pics 3 & 4)





    The Level II ROM set has hand-written labels ??? (pic 5)



    There is an add-on board mounted above the keyboard on the right side (pic 6) with lots of wires going to the slide switches and the motherboard (pic 7)





    The motherboard itself (pic 8 ) has a small added board and lots of extra wires (pics 9 & 10)







    This is the 5th Model I in my collection, but none of the others are anything like this one. Any thoughts/info appreciated.

    Mike

  2. #2
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    Just eyeballing it I'd guess the DB9 connector is for an Atari 2600-style joystick. (Looks to me like they soldered it so it'd actuate the directional arrows and the button is the spacebar.)
    My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs

  3. #3

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    The DE9 looks like an Atari joystick port, mapping the joystick directions to the cursor keys and fire to the spacebar.

  4. #4
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    I'd love to know what's on that white EPROM chip bodged onto the middle of the board. It looks like it's a 2kx8 2716-equivalent; if you PEEK around over the 12k mark (where ROM usually ends in a stock Model I) do you see signs that the ROM is mapped in there? Sometimes people would stick things like faster cassette routines or a keybounce fix onto a ROM and set it up so they could activate the contents by running a SYSTEM command after starting BASIC.

    Re: the switches, have you tried stopwatching a FOR loop with them in different positions? Some of that hacking could be a speedup mod. There is a remarkable amount of hacking, though, I must say.
    My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs

  5. #5

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    The keyboard stickers look like Scripsit keys to me. (Note: I did not spend more than two seconds thinking about this, and am possibly entirely wrong about it.)

  6. #6
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    Where do the wires attached to the switches go?

  7. #7
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    My first thought on the DB-9 connected to the keyboard was for an Atari joystick. Something I'll check when I get it running more smoothly.

    All of the wires on the switches are visible, connected to the motherboard or the small add-on board. Both switches in forward position have no wires (normal mb operation?), in the rearward position they connect the add-on board to the motherboard.

    Mike

  8. #8
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    Whoever did those mods did a *beautiful* job cutting the holes for the switches and joystick port.
    [Need something to waste time on? Click here to visit my YouTube channel CelGenStudios]
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  9. #9
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    Backside of the little board and the switches:



    Z26 is piggybacked with a 74LS74
    Z27 is piggybacked with a 74LS36
    Z55 is piggybacked with a 74LS02

    Everything that can be reseated has been, so on to reassembly and retesting.

    Mike

  10. #10
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    The EPROM appears to be in Z29's position, suggesting it is a character generator ROM replacement. It's probably a lower case ROM upgrade. Some of the mods around it may be for additional scan lines like the "Don Mod" from Australia supported.

    Tom

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