[Coco] CoCo 1 'E' board memory upgrade

[Brian Blake]

After looking over my first miserable attempt at diagramming the changes to
this board, I started over. It appears all of the connections mentioned in
the tech bulletin are present and correct, except the position of the Hi/Lo
jumper:

https://cmtekwerx.com/comparo2.jpg

I'll swap the 4164's out tonight, throw some Holy Water down around it,
wave some chicken bones, and see what happens.


It appears I do have one CoCo 1 with the Rainbow style upgrade - the
jumper from U29 pin 5 to TP1 is present. This CoCo (along with my white
CoCo) will play Sailor Man, and presumably run OS9 Level I.

https://cmtekwerx.com/rainbow-upgrade-2.jpg


Thanks for the sanity check, guys!



On Tue, Apr 16, 2024 at 4:29 PM Bruce W. Calkins via Coco <
coco at maltedmedia.com> wrote:

> Early Radio Shack 32K upgrades were often half good 64K chips, hence the
> high/low jumper.  Personally, I've never seen a half good chip, but I
> recycled many IBM 64K chips which had to be good for 64K.
>
> Bruce W.
>
>
> On 4/16/24 16:18, Brian Blake via Coco wrote:
> > See Below:
> >
> > On Tue, Apr 16, 2024 at 11:23 AM RETRO Innovations via Coco <
> > coco at maltedmedia.com> wrote:
> >
> >>
> >>
> >> I've never done this mod, so feel free to ignore, but I thought I'd map
> >> it out and see if I can help answer the question
> >>
> >> U29 is 74ls02, and pin 4 is an output (it's a quad 2 input NOR gate, so
> >> NOT(A or B))
> >>
> >> U29:pin 1 is also an output
> >>
> >> U11 is 74LS138 and pin 1 is an input (it's the A of the 3 inputs [a,b,c]
> >> that make up the 3 bit number, so to speak)
> >>
> >> pin 5 is Also input, it's a enable input !G2B (it's an active low input,
> >> meaning that the '138 outputs will be valid only when this pin is at
> >> ground)
> >>
> >> So, U29:1 is connected to U11:5, output to input.  Output to input is
> good.
> >>
> >> Now, the instructions are noting connecting U29:4 (output) to U11:5
> >> (input).  Output to input is good.
> >>
> >> But, then that means two outputs (U29:4 and U29:1) are connected to 1
> >> input (U11:5).  Two outputs to 1 input is bad.
> >>
> >> So, no, you should not connect both U29:4 and U29:1 to U11:5.
> >>
> >
> > I did not believe so either, I just needed a sanity check.
> >
> >
> >
> >>
> >> So, I checked the actual technical bulletin for the CoCo 'E' upgrades,
> >> and what I saw was the 64kB upgrade, which appears to make the same mods
> >> shown on your PCB:
> >>
> >>
> >>
> https://colorcomputerarchive.com/repo/Documents/Manuals/Hardware/Color%20Computer%20Technical%20Bulletins%20(Tandy).pdf
> >> It's bulletin 15, which starts on page 28, and the Rev E instructions
> >> start on page 33.
> >>
> >> Can you verify the mods shown on that TB are applied as per the
> >> instructions?  If so, are you sure you don't already have 64kB in place?
> >>
> >
> > I'm going to double check those against the board to be sure - thanks for
> > the TSB, I had never seen that. Guess I need to peruse the archive a
> little
> > closer.
> >
> > All I have to go on is the fact that the machine will not load or play
> the
> > game Sailor Man by Tom Mix, which requires 64k. It will load and play
> > Donkey King/The King, though the intro music and 'Mario's' footsteps
> seems
> > to play faster than norma, so there may be an underlying issue somewhere.
> >
> > First thing I guess I'll do is swap out the older RAM chips and put in
> some
> > new ones, and make sure the jumper for Hi/Low is set properly (I believe
> > Low is what the doc I was reading said)
> >
>
> --
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> Coco at maltedmedia.com
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>


-- 
Ohioan by birth, Floridian by the grace of U-Haul and a bad economy...
--------
Sarcasm is the body's natural defense to stupidity.