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Thread: Model I Issues

  1. #11
    Join Date
    Mar 2013
    Location
    Chaffee, MO
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    1,606

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    Don,
    Do you have a camera that has MACRO Mode where you can get a good clear picture of the first four characters
    that are displayed on the monitor?

    It sure looks to me like the Model 1 is trying to display the "@9@9", but it looks like it's some type of graphics
    character. I extracted the Graphic Characters and none of them look sane or similar with what you are seeing.

    I've attached that PDF page.

    Larry

    Level-II-C5.pdf

  2. #12

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    I don't have a camera with macro mode. I did manage a picture taken through a high powered magnifying glass. There are no identifying characters that I could see with the 30X magnification or with the naked eye. The DIP shunt at Z3 was removed.

    20201011_114337.jpg
    - Don Mankin -

    [
    TRS-80 Models I, 4, 4p, Coco 2, 100, 102. Tandy 1000 RLX. Osborne 1a.
    At
    ari 800, 520 STm. Commodore 64.
    Amiga 1000. TI-99/A. Sinclair ZX-81]

  3. #13
    Join Date
    Mar 2013
    Location
    Chaffee, MO
    Posts
    1,606

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    Don,
    Try your Phone. I just powered up my Model 4 and took this picture as I zoomed in a bit.
    At least maybe we can see what the characters are.

    You can email me the picture.

    Larry

  4. #14

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    I don't see the picture you took and can't locate your email address. In any case, here is a picture I took with my Samsung Galaxy S8 in macro mode. Again it shows no discernible characters whatsoever.

    20201012_103716.jpg
    - Don Mankin -

    [
    TRS-80 Models I, 4, 4p, Coco 2, 100, 102. Tandy 1000 RLX. Osborne 1a.
    At
    ari 800, 520 STm. Commodore 64.
    Amiga 1000. TI-99/A. Sinclair ZX-81]

  5. #15
    Join Date
    Mar 2013
    Location
    Chaffee, MO
    Posts
    1,606

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    Don,
    Why don't you have a look at the Pins 2 & 3 of Z30 (74LS02) to see if CHARACTER or GRAPHICS is enabled from
    Z10 or Z11 (74LS166). It looks to me like you have a problem with Z27 (74LS175) around the Signals
    DLY L8, DLY BIT7, or DLY BIT7*. If Graphics is enabled to Shift/Load Z11 (74LS166) versus CHARACTER
    Z10 (74LS166) that would make sense of the crazy characters we are seeing versus a Character.

    A quick check on the Input Pins of Z30 (74LS02) Pin 3 = HIGH = CHARACTER, or Pin 2 = HIGH = GRAPHICS
    should show which 8-bit Shift Register's Data is being sent to the Video Display.

    Suspect IC's could include Z27 (74LS175), Z26 (74LS20), and Z30 (74LS02).

    It shouldn't take long to see what is going on.

    Larry

  6. #16

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    Larry... I'm not sure my logic probe is working correctly. Both pins 2 and 3 of Z30 caused the probe to blink both hi and low at a high rate of speed. The probe instructions says it's blinking at the square wave frequency rate.
    - Don Mankin -

    [
    TRS-80 Models I, 4, 4p, Coco 2, 100, 102. Tandy 1000 RLX. Osborne 1a.
    At
    ari 800, 520 STm. Commodore 64.
    Amiga 1000. TI-99/A. Sinclair ZX-81]

  7. #17

    Default

    Quote Originally Posted by Fooser View Post
    Larry... I'm not sure my logic probe is working correctly. Both pins 2 and 3 of Z30 caused the probe to blink both hi and low at a high rate of speed. The probe instructions says it's blinking at the square wave frequency rate.
    BTW I get the same condition from the probe when I touch it with my fingers.

    And I get 0 volts on either pins.
    - Don Mankin -

    [
    TRS-80 Models I, 4, 4p, Coco 2, 100, 102. Tandy 1000 RLX. Osborne 1a.
    At
    ari 800, 520 STm. Commodore 64.
    Amiga 1000. TI-99/A. Sinclair ZX-81]

  8. #18

    Default

    I found my other probe and pin 3 of Z30 is definitely low. Pin 2 caused the probe to blink both hi and low at a high rate of speed.
    - Don Mankin -

    [
    TRS-80 Models I, 4, 4p, Coco 2, 100, 102. Tandy 1000 RLX. Osborne 1a.
    At
    ari 800, 520 STm. Commodore 64.
    Amiga 1000. TI-99/A. Sinclair ZX-81]

  9. #19
    Join Date
    Mar 2013
    Location
    Chaffee, MO
    Posts
    1,606

    Default

    Don,
    OK, Check the Shift Register(s) Pin 15 (LOAD) for a HIGH Pulse. Z10 & Z11 74LS166 are loaded by
    Z26 74LS20. Pin(s) 6 & 8 are the "HIGH" Load Pulses.

    Larry

  10. #20

    Default

    Both are pulsing high.
    - Don Mankin -

    [
    TRS-80 Models I, 4, 4p, Coco 2, 100, 102. Tandy 1000 RLX. Osborne 1a.
    At
    ari 800, 520 STm. Commodore 64.
    Amiga 1000. TI-99/A. Sinclair ZX-81]

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