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Thread: Next Challenge: Hyperion that won't display text

  1. #11
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    I wonder... would it be possible to dump the EPROM from within dos? I am wondering if I can rig something up to do that automatically and write it to a txt file. Then I could see if mine is any good.

  2. #12
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    Okay so I have read the circuit description more and am starting to (I think) understand how different parts of the display board work and interact with each other. I can see for example the line that goes high or low based on whether the machine is in alphanumeric mode or graphics, and I can observe that line working as the machine loads Kings Quest. I can see data moving between the char gen EPROM and the attributes controller. The EPROM determines which characters to display, the attributes controller determines things like whether characters are underlined or blinking or superscript or subscript. I can see how super script and subscription attributes are triggered on or off in their own section.

    One line that has caught my attention is CB3. According to the description, if CB3 is high, the character bits are passed unmodified past the attributes controller. If it is low, the attributes controller determines and applies the changes, like superscript or doublewidth and then modifies the bits to have those attributes.

    What I am seeing right now is that CB3 is always low. So if I'm understanding right, this is forcing the attributes controller, which is a little iffy, to try to modify the text to be displayed. To what, I don't know. The super/subscript circuit is inactive, so it's not that. I don't think it's anything.. I think CB3 may simply be stuck low and maybe that's why it's producing nothing, because the attributes controller isn't getting any instruction on how to modify.

    I think an experiment for tomorrow would be to figure out a way to either force CB3 high, or force one of the attributes (like underline) high to see if we get anything passing through the controller.

    I've traced CB3 on the schematic back to (I think) my old arch nemesis... the 74LS273. I've tangled with these in several old video circuits and they do seem to have a higher than average fail rate.

    Anyway... I'm not sure how I'll force CB3 or one of the attributes high.. but I'll figure something out.

  3. #13
    Join Date
    Dec 2005
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    Quote Originally Posted by snuci View Post
    The white one shown here? Yes. Surprisingly in good shape in all cases I've seen.

    http://vintagecomputer.ca/wp-content...behind-CRT.jpg
    2 out of 3 of mine are fine; the third one did start to leak.

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