Re: Display weirdness with IIe?

[dempson@actrix.gen.nz (David Empson)]

Gareth <cuillin@my-deja.com> wrote:

> The composite video output (PAL) on my IIe is acting strangely. When
> in "normal" text mode, the background intermittently changes colour,
> from brown-ish to solid black to a kind of slightly red-ish. It
> especially happens in sync with disk drive operations.
> 
> However, when in a graphics mode (e.g. playing Choplifter), there's no
> problem at all - the colours remain rock-solid.

This sounds like some kind of interference with the "colour killer"
circuit.  This part of the motherboard circuitry is responsible for
disabling colour signals on the composite output while the video display
is operating in text mode.

That's all I know about it without having a hunt through various
technical documentation, which is not within arm's reach tonight.  :-)

As an experiment, you could try changing the colour disable DIP switch
(centre right of the motherboard): it should also kill colour in
graphics mode if enabled; you might then get the same colour effects
while there is disk activity.

A possible explanation might be variations in the power supply voltage
when the disk drive is active.