16 Mar
2010
16 Mar
'10
1:45 a.m.
On 3/15/2010 4:15 PM, Tony Duell wrote:
1) Have
you tried adjusting the 14.3...MHz clock trimmer in the PC? The
original IBM machines (including the 5161 expansion unit), and many older
clones, have a trimmer across the crystal that's used for the 14.3...MHz
oscillator (this is divided down to get the 3.58...MHx NTSC colour
reference, of course). The IBM manuals recomend adjusting this if the
colours are misisng/incorrect. I am not sure it will do any good, but it
can't hurt.
I have tried, and all it does is change the hue (slightly). It doesn't
make the colors any closer to their RGB equivalents.
Mind you, some of the color combinations possible in composite color
mode are fantastic
2)If the colours are wrong but consistent, can't
you modify them after
digitising them?
Not easily. It's an analog capture and there are luma/chroma cross-talk
issues that make things worse. I would only do that if desperate, and
it still wouldn't look right.
3) Take a look at the CGA monitor schematic,
particularly the part from
the RGBI TTL inputs to the CRT cathodes. This will show you how the 4 TTL
signals are combined to produce analogue RGB signals.
I would need to go to school to understand what I would be looking at.
But my brother works at UL as a tester and has an electronics degree, so
I will ask him.
--
Jim Leonard (trixter at oldskool.org) http://www.oldskool.org/
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