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Thread: TRS-80 Coco 2 Color displays incorrectly HELP!

  1. #1

    Question TRS-80 Coco 2 Color displays incorrectly HELP!

    Hello all,

    I recently bought a TRS-80 coco 2 (26-3026) with the 64k upgrade. The system powers on and runs both basic and games easily. If I run a color test program, in basic, all the colors show up correctly, However in games (Demon attack, Canyon Climber, Dungeons of Daggorath) all the reds and blues become pink and green.

    I have tried a few different methods to fix this, one of which is to bridge pins 10 and 11 on the VDG (u8) which fixes the color in games, but makes all the colors in basic are completely off (Red is purple, colors are faded, etc)

    I've replaced capacitor C26 which helped the video signal, but the colors are still off.

    Anyone else having this issue? Any ideas on how to fix this? Would the triple 5 timer(u4) have something to do with it? Is there something I am missing?

    Appreciate any help i can get! I can take photos as well if that helps.


  2. #2
    Join Date
    Feb 2017
    Chilliwack, BC, Canada


    Are you using a CRT or an LCD as monitor? For the LCD I use, I always need to fiddle with the RF tuning to get the colour to display properly, but that could also just be result of the cheap cable I kludged together. Maybe the background colour is causing the ADC in the tuner (if it's an LCD) to mess up the colour?

    Otherwise, I'd try to find or write a memory tester program, 'cause you might have flaky RAM.
    CoCo2 Memory Map
    My vintage systems: Tandy 1000 HX, Tandy 1000 RSX, Tandy 1100FD, Tandy 64K CoCo 2, Commodore VIC-20, and some random Pentium in a Hewitt Rand chassis...

    Some people keep a classic car in their garage. Some people keep vintage computers. The latter hobby is cheaper, usually takes less space, and is less likely to lead to a fatal accident.

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