Re: Asteroids proper grounding and monitor DC reg bug.

Matt J. McCullar wrote:
>
>
> I[Matt J. McCullar]
> It's really simple. To prevent weird things from happening, just
> make sure that each major piece of the game has only one ground
> connection. If you have more than one cable connecting two
> points, not only is that redundant, but currents can start
> flowing where you don't want them to.
>
> Think of a bicycle wheel with all the spokes. Remove the outer
> rim so that all the spokes fan out in a star pattern. If we
> consider the central hub to be our main ground connection, and the
> end of each spoke to be a different piece of our game cabinet
> (motherboard, video monitor, etc.), then each spoke has one and
> ONLY ONE way to connect to ground. If the outer rim were in
> place, then currents would start flowing between one or more
> spokes on their own... and we don't want that.
>
> I really have been trying to follow this conversation but my head
> is swimming. Could someone please sum up what they consider the
> best course of action is in grounding a vector game in layman's
> terms. ....I knew I should have stuck to my EE major.
>
Well, it is not quite that simple. Certainly when one is designing a
product and wishes to use the best possible design to eliminate ground
loops, electrical noise, and other oddities - one designs using the
single Star (Common) system.

Unfortunately in the real world the star system breaks down at the
junctions and then you get problems with different ground potentials
building up between various sub-components in the system.

Now, if you are passing signals to each component via an isolated path
(optical isolators for example) then these ground variations do not
matter. However when dealing with Vector monitors - primarily the
Sega/GO-8 system - when the grounds start to fail (not if - when) then
the ground reference for the X & Y signals drifts with the ground fault.
This can lead to ground/common voltage differences between
sub-assemblies which can be enough to bugger up the bias of the XY
deflection circuit so the output transistors are pushed into illegal
drive states (my supposition), leading to failure.

So, I (and others) recommend that a SECOND ground/common star is
installed to add redundancy to the system and help prevent this problem
from occurring.

This second ground/common IS redundant in a well maintained game
(polished power connectors that run cold to the touch), but in many
games this is simply not the case and the second ground system will
protect (if installed correctly) as the primary ground/common was
designed to do - but fails due to connection issues developing over time.

Please note, I am NOT an electrical engineer, rather a self-taught
technician who found this solution back in the mid-1980s (originally
figured out for Gottlieb Pinball Games that were blowing coils at
random) and I have since found that this solution works in most power
systems that use a common ground and where these ground/common junctions
are not bolted together.

John :-#)#

-- 
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9 
Call (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, VideoGames)
                 www.flippers.com 
"Old pinballers never die, they just flip out"
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