[Coco] New thread, cga-rgb->vga convertor GBS-8220

[gene heskett]

On Wednesday, July 27, 2011 10:01:45 PM RJRTTY at aol.com did opine:

> In a message dated 7/27/2011 6:28:44 P.M.  Eastern Daylight Time,
> mmarlette at frontiernet.net  writes:
> Gene,
> 
> >There is an adjustment pot that will allow your  display to be cleaned
> >up
> 
> with Roy's.
> 
> >Just not sure which one it is  ATM....Roy?
> >
> >Quartus 11.0 is currently working overtime........  :)
> >
> >Regards,
> >
> >Mark
> >Cloud-9
> 
> You  can play with the gain control on my converter and eliminate a
> lot of the  noise depending on which version you have.  The new
> ones I make now use  input filters to capture enough of the noise
> without sacrificing sharpness  that the noise can be eliminated
> from the image at the proper gain  setting.
> 
> I usually end up adjusting converters at the fest to  minimize the
> noise in the unique setup of each individual  user.
> 
> Roy
> 
One thing that may have a bearing on both the noise and the crispness of 
the video was the discovery that on _my_ mobo, the silk screened position 
FB5, which is supposed to have a Ferrite Bead installed, actually had a 2.2 
ohm resistor, this in series with the 5 volt Vcc for the gime.  Downstream 
of that resistor, the gime was trying to run on about 4.79 volts.  This 
lowered Vcc voltage compromises the gime's video ability in terms of its 
video rise and fall times, which were about 240ns!  With a real ferrite 
bead bridged across that erroneous resistor, the gime is getting about 4.98 
volts from a 5.02 volt input from that old AT power supply.  That 199 
millivolt rise in Vcc cuts the video rise and fall times to less than 90ns!

Now I wonder if this is a common fault in lots of coco3's and was hidden by 
the poor performance of the CM8 usually sold for a coco monitor?

One thing this 8220 board has is a digital sharpness control that must work 
something like a comb filter.  Set at about 1/2 full scale, its pretty 
decent.

> 
> --
> Coco mailing list
> Coco at maltedmedia.com
> http://five.pairlist.net/mailman/listinfo/coco


Cheers, gene
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
panic("Foooooooood fight!");
	-- In the kernel source aha1542.c, after detecting a bad segment 
list