trs-80 model II trouble

Fred Cisin cisin at
Tue Dec 15 17:15:54 CST 2009

On Tue, 15 Dec 2009, Bob Brown wrote:
> When I close the diskette door, the exclamation points turn non-inverse
> but still cover the screen.
> It when boots (in this case I am booting a cpm disk).
> The letters seem jumbled up...after booting, I see:
> "CQ/MQ!for!tss-81 MOEM II
> 63k!Version!2/25A
> Copyrigit!(c)!1981 Migecoat Associaues"
> And it goes to a command prompt.
> The rest of the screen is still filled with exclamation points.
> The system does respond as I type things, but letters are garbled.
> Any ideas?  Does this sound like some bad memory?  How can I diagnose
> this?

Make a quick chart.  Write down the binary bit pattern for the ASCII codes
of the letters that you are getting, and in the other column, write down
the bit patterns for the ASCII codes of the characters that you think that
they SHOULD be.  Use an ASCII chart if you need to.
("Migecoat" should be "Lifeboat")

Notice the pattern.  In this case, the pattern and the problem will be
obvious once you make at least part of that chart.

Now find the video memory.

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