[Coco] Coco RGB to SVGA

[Roy Justus]

Dear coco friends,


      I have nearly recovered   from illness and loss of my data files
so I am getting ready to restart production of my converter.

      I also  want to discuss some aspects of the process of conversion
of Coco RGB.     First is the noise some see with early version of my
converter.   Most common is the vertical bands seen during use.
Another is the distortion seen with some foreground/backround
when viewing 80 column text.   Typically the blue in a cls(7) backround
in SECB.   At first I tried to eliminate this noise  but had little
success doing it.

     The basic problem is this noise comes out of the GIME chip and
not from any outside source.    The reason it didn't show up in the old
15 khz CRT displays is that they naturally filtered the signal due to thier
low bandwidth response. 

    The second problem is that my earlier converters and other commercially
availible units have a hard time keeping an LCD display locked.    LCD's have
such highbandwith the noise coming out of the GIME confuses them and they
shut down.

    If you want to use a converter that won't sync to an LCD try it on a older CRT SVGA
display.    This applys to my old units and commercially availible ones.

    To  address these problems I have lowered the bandwith of my converter with
some low pass filtering on both the data lines and sync inputs.    I have also changed
the PLL tank circuit values to address the phase lock problems.   I have tried my
new converter on no less than five "picky" LCD's and they stay on and sharp.

     Another problem is the price of my converter.      It cost approximately $100 per
unit to build but I think that is way too high.     I  am going to offer a board level
unit for $40  and  a unit with enclosure for $60.   I don't do this to make money.
i do it because monitors for the Coco3 are becoming very rare and I enjoy it.

   So let's light up the summer with coco3 displays and send me your 
order for one.    A board level unit comes with all the connections for
a great repak project and the unit in with enclosure looks good on the
shelf with the coco3.



Roy Justus
rjrtty at aol.com