Re: IIgs video problem

["Michael J. Mahon" <mjmahon@aol.com>]

James Littlejohn wrote:
> I have 2 GS's with problems. I will make a new post for the other
> question.
> The first has problems on the composite out. The top half of the
> screen is not stable, it wiggles, but the bottom half is rock solid.
>
> I have tested the monitor, and it works great on my other Apples.
>
> Suggestions on where to start changing parts?

First, I assume you mean that the picture "wiggles" from side
to side by a small amount ("flagging")--is that the case?

And is the lateral displacement larger the closer you get to the
top of the screen, eventually disappearing as you get further down?

If so, then I suspect that the sync part of the signal is too small.

It should be about 25% of the composite signal amplitude when viewed
on an oscilloscope.

The sync is mixed into the video with a transistor driven by a gate.
The transistor may be weak or the gate output substandard--or a resistor
in the mixing network may be out of tolerance.

If it's not flagging, but some other kind of displacement, then this
doesn't apply.

BTW, how does the video look on another monitor?

-michael

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