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Thread: Are all CGA/EGA monitors white if they are not plugged in to a powered PC?

  1. #1

    Default Are all CGA/EGA monitors white if they are not plugged in to a powered PC?

    I noticed this with my IBM 5153. Bright white if the 5710 is off or it isn't plugged into it. I see an IBM EGA monitor on eBay and they powered it up and the same thing. Is this normal for all CGA/EGA monitors, or just some? Maybe if they had a pull down or pull up resistor on incoming lines it would be different?

  2. #2
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    Quote Originally Posted by alank2 View Post
    I noticed this with my IBM 5153. Bright white if the 5710 is off or it isn't plugged into it. I see an IBM EGA monitor on eBay and they powered it up and the same thing.
    Per the 'Power up' links in the IBM 5153 and IBM 5154 sections of [here].

    Quote Originally Posted by alank2 View Post
    Is this normal for all CGA/EGA monitors, or just some?
    My early NEC monitor (EGA/CGA/MDA) does not do the same.

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    My TVM EGA GA monitor goes white if the video cable is pulled or computer is turned off.
    Thomas Byers (DRI)- "You'll have a million people using the A> [MS-DOS prompt] forever. You'll have five million using [nongraphic] menu systems such as Topview, Concurrent PC-DOS, Desq, and those types. But there'll be 50 to 100 million using the iconic-based interfaces."

  4. #4

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    At least on the 5153 as I recall, the RGBI signal at the inputs to the logic gates are tied with a resistor to 5V and a resistor to ground, of a ratio that sets logic high for the gate they feed, a 74S05 I think. The input impedance is very roughly the value of the two resistors in parallel and this acts as a termination for the signal cable to help prevent reflections and delays from the cable's capacitance. So if the cable is out, R,G&B are assumed "on" so the screen is white.

    Some monitors though use the H sync pulses for signal clamping in the video stages, so if the sync is not there the screen goes black, it depends on the particular design.

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