Re: Asteroids proper grounding and monitor DC reg bug.

js@cimmeri.com wrote:
>
>>>
>>>
>>> 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 :-#)#
>
> Ok, I'm glad John clarified because this is an important point. John
> is talking about adding another (and better) ground as both a failsafe
> and also to get better current flow where lousy connections exist.
>
> What I'm discussing is somewhat the opposite: *removing* any
> redundancy (which can lead to ground loops and potential problems from
> having them), and essentially re-engineering the original lousy
> connections, wiring, and main grounds to establish an improved ground
> scheme.
>
> Our goals are the same, but the methods differ. John's suggestions
> are far better than having lousy grounds, no doubt. My suggestions
> are harder to pull off, and have to be very well-made (and perhaps
> even occasionally maintained) because you're relying on single point
> connections.. there is no redundacy.
>
> Note that John's ideas sprung from the electromechnical world where
> ground loops aren't as problematic as in the audio, video, and digital
> worlds.
>
> JS
>
>

Electromechanical (EM)? Pinballs had been electronic since the mid to
late 70s...now, what does one call that system? Digital-Mechanical?
(DM?) (possibly ducking).

Gottlieb was on their second generation digital pinballs by 1980.

At this time Gottlieb pins electronics were designed by Rockwell
engineers and that explained why they were having trouble with coil
failures - Rockwell designed a proper system using a star ground, but
they allowed no redundancy.

At the same time Williams, and to some extent Bally/Stern (only two
bolts per board that operators often didn't bother with) did bolt all
the boards to a common ground plane and this greatly reduced the random
coil meltdown that Gottlieb pinball games experienced.

This ground issue served to gave Gottlieb a very bad name for
reliability - from number 1 during the EM period to number 4 in the DM
(Digital Mechanical) period...sounds a bit like SEGA & the Electrohome
XY flame festivals.

Again this problem with XY monitors happened a few years before I
discovered the root cause in the mid-80s...

(toot-toot)

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"
-- 
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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