[Coco] Monitor proboems

[Gene Heskett]

On Friday 27 December 2013 16:26:52 Bill Gordon did opine:

> Does anyone else have a Roy Justice monitor converter?
> I've finally been able to get it set up, and NitrOS-9 is IMPOSSIBLE 
> with the converter and monitor.
> The screen does fine while NitrOS-9 is booting, right up until I get the
> {Term|02}/DD: prompt. After that, it flashes a few times, then comes
> back on, but continues to flash-mostly staying black. In RSDos,
> everything is perfect. It comes up and doesn't falter a bit.
> I don't know if it's the converter or the monitor. I've tried it with
> other monitors and another Coco3, and it does the same thing.
> (Ideas?)
> Thanks

I have had several, the latest, a long one only about 2.5" wide, has now 
work flawlessly for nitros9 for going on a couple years now.  The earlier 
one did tend to do that, very noticeable flickering when any hardware 
interrupts were in use.  I traced that down to an item on the motherboard 
that was labeled as FB5 on the schematic, supposedly a 6 cent ferrite bead 
on a wire about 3/16" long that fed the 5 volt bus into the gime.  It is 
located adjacent to pin 35 on the gime, and was dropping nominally 100 
millivolts across it because the guru's at radio shack used a 10 ohm, 4 
cent chip resistor to reduce costs in my coco3.  The gime is extremely 
sensitive to its applied VCC, and a small jumper across it, raised the 
output video levels considerably, and got rid of the IRQ interference 
almost completely.  So if you find a chip resistor that reads about 10 ohms 
sitting on artwork that says FB5, jumper it.  Since my coco3 is running on 
an elderly AT psu, and I have a full 12 volts available, (which also burned 
up my SALT when inetd got into a fight with the 4.3.3o server jar) I may at 
some point build an adjustable 5 volt supply running on the 12 volt line, 
removing both that chip and the jumper, and feed about 5.1 volts to the 
left pad that feeds the gime, adjustable upward, and see where its real 
sweet spot might be without actually getting it too warm.

The RGB outputs on mine are slow, so slow that the low amplitude anyway 
blue output is about as useful as the belly appendages on a boar hog.  
Best, full amplitude swing on the G line is about 250ns, and even NTSC 
allows for something in the 110 to 120 ns area for full sharpness.

Unfortunately, 1987 Gime's aren't available from any source that isn't 
treating them like a ransom money source. I'd take 2 if it didn't run my 
card to empty.

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)
Genes Web page <http://geneslinuxbox.net:6309/gene>

There can be no twisted thought without a twisted molecule.
		-- R. W. Gerard
A pen in the hand of this president is far more
dangerous than 200 million guns in the hands of
         law-abiding citizens.