[Coco] So is this a G board?

[Gene Heskett]

On Saturday 29 June 2013 09:27:01 Darren A did opine:

> On Fri, Jun 28, 2013 at 6:39 PM, Luis Antoniosi (CoCoDemus) wrote:
> > I confirm that cutting C77 solves the issue Now it runs the sIDE
> > without any problem.
> > 
> > Even the game The Keys of the Wizard is working now, this games uses
> > the speech sound pak, could it be related ?
> 
> Why the engineers added that capacitor to the 'F' board design is a
> mystery. It seems to serve no purpose other than to cause
> malfunctions.  The 'D' and 'E' board CoCo 1 doesn't have it and I'm
> fairly certain none of the CoCo 2 or 3 boards have it either.
> 
> Darren
 
That was the FCC at work Darren.  The coco's made too much broadband 
digital noise.  Not in those days being able to vapor deposit a metallic 
film on the inside of the case to shield it all, at a price per case that 
was affordable, they tried to identify and slow down the offending signals.

The commissions rules for home devices are tighter than for industrial use, 
justifiably so IMO, but there weren't any provisions that would have 
allowed a noise suppression method to be bypassed if it disabled the 
device, that was tough cookies.  Tiny capacitors and low value resistors 
were and are yet, cheaper than ferrite beads, which provably would have 
done a better job, but like the coated and shielded cases, never got past 
the bean counters in Ft. Worth.

FWIW, in my coco3, the video had always had a huge flicker that was IRQ 
related, very obvious when it was online downloading something with 
supercomm.  It took quite a while, scattered over several years to find it 
but I finally found it!  What was labeled on my schematics as a ferrite 
bead (FB) in the power supply Vcc line to the GIME, was in fact a 10 ohm 
resistor as it was much cheaper than the FB called out on the schematic. 
Near the right front corner of the GIME's socket, I managed to paste a bead 
on a small bit of wire across that resistor, and I immediately had a much 
brighter, noiseless video output.  The GIME is an extremely voltage 
sensitive chip, and if I could rig a 5.5 or 6 volt supply, only for the 
GIME, I sure would.

Cheers, Gene
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