36948Re: TRS-80 available in central NJ
- Jul 26, 2014Nope, not missing any cables.
The TRS-80 Model I had several revisions to try to correct a problem with
RAM errors in the Expansion Interface.
I don't remember what order they came in, but I believe it's...
1. Original release that tried to use a straight cable, but noise over the
cable caused errors in accessing the RAM in the E/I.
2. A buffer box on the cable was an attempt to clean up and strengthen the
signals to and from the E/I.
3. A buffer box AND a shielded DIN cable that sent the memory timing signals
from the Model I keyboard to the E/I. This is the unit I rescued.
4. A redesigned E/I that generated the memory timing signals inside the E/I
and didn't rely on the signals sent through the flat cable.
You can't mix and match a DIN cable E/I with a non DIN cable keyboard unit.
And a buffer box unit can't be used with a straight cable as a no-connect on
the expansion bus is modified with 5v to power the buffer box. It would
damage the keyboard unit to try to use it.
We think a latch in the video section is bad, as instead of text, I see
graphics characters. I have to dig out the schematic, see which latch choose
the character generator ove the graphics characters and replace it. We tried
to type "CLOAD" to try to hear the cassette relay click to see if the system
was working that much, but pressing the "A" key produced no characters. Once
I get the rest of the system working, I'll work on the keyboard.
The Model III is working with one drive, but they keyboard isn't working
right. Many keys do not work. Unfortunately, this key board is the model
where you have to desolder the station, take it apart, clean it and resolder
it again. A big job to fix it.
-[ Al ]-
Posted by: "John Ruschmeyer" jruschme@... jruschme
On Fri, Jul 25, 2014 at 8:23 PM, Al Hartman alhartman6@...
[midatlanticretro] <firstname.lastname@example.org> wrote:
> We went to pick up the TRS-80 Model I. After stopping at Applebee's forIt sounds like you're missing the ribbon cable from the CPU (keyboard) to
> lunch (Outback wasn't open for lunch), we got the unit home and set it up.
> It appears to have something wrong with the keyboard unit as it starts up
> with graphic characters all over the screen. Also, the "A" key does not
> appear to work.
> It's a unit with the DIN cable going from the keyboard to the expansion
> interface, so it won't work with my other keyboard unit.
the EI. As for the DIN cable, if memory serves, that is just the normal
power supply relocated to inside the EI for convenience. I may be
misunderstanding something, but you should be able to use your other CPU
just fine (just need the ribbon cable).
At least that is what I seem to recall as it has been about 20 years since
I touched my old Model I.
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