Just got a "highly" modded Model I - questions

[MikeModifed]

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

 

[Eudimorphodon]

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.)

 

[wmcbrine]

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

 

[Eudimorphodon]

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.

 

[bear]

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.)

 

[lafos]

Where do the wires attached to the switches go?

 

[MikeModifed]

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

 

[NeXT]

Whoever did those mods did a *beautiful* job cutting the holes for the switches and joystick port.

 

[MikeModifed]

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

 

[hornbetw]

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

 

[MikeModifed]

Thanks for all the input, guys! Keep it coming. More coming tomorrow.

Mike

 

[MikeModifed]

I got it running nicely, the video no longer jiggly. It has an interesting, almost elegant, semi-sans-serif font:

The EI appears to be completely factory original. It has, though, a sticker I haven't seen before:

Mike

 

[lafos]

Never saw a sticker like that. Wonder if it was specific to a computer center? Does the EI have RAM? The 26-1140 was sold with none.

 

[MikeModifed]

Ram? Yes. Two differing sets of non-RS chips, and an Aerocomp doubler:

Mike

 

[MikeModifed]

Creative Computing had an article on the joystick mod in 1982 or 83. One wire difference and they strangely cut the DE-9 off of the Atari joystick and hardwired the joystick to the keyboard.

https://ia801705.us.archive.org/23/...TRS-80_1983_Creative_Computing_Press_text.pdf page 29 of the book, page 38 of the pdf.

Mike