Re: Star Trek pic waving?

The waving picture problem is solved !!! As suggested below, I just removed the extra ground lead that I had added from the monitor and the problem went away. The picture is rock steady now. Thanks to everyone!

I guess this means that rather than adding another ground, I should aim to improve upon the ground connections that are already there. What I had done that created the wave was I had added a heavy wire that runs between the metal frames of the power supply and the monitor and also the metal game cage. I guess I learned the hard way that this wasn't the proper way to tie things together. The grounds that I should focus on are not the chassis/earth grounds, but rather the 0V references or "circuit" grounds. Yay! Time to play!

William Boucher
  ----- Original Message -----
  From: John Robertson
  To: vectorlist@vectorlist.org
  Sent: Friday, November 27, 2009 1:44 AM
  Subject: Re: VECTOR: Star Trek pic waving?

  kstillinger@sc.rr.com wrote:
I had a G08 on the 'bench' this Summer.

  I had gone through some of the usual troubles to get it going. It was looking pretty crisp and bright and there was but one flaw-
  the little horizontal scrolling noise line every few seconds.
Same as what you're describing from what I can tell.

I had always read the normal statements about good ground connections between parts and all.
Well, I don't know about GOOD ground connections, but I had a multitude of alligator clips between the monitor frame, transformer, power supply, card cage, o-scope, just about everywhere.

  I was trying to measure some AC ripple at different points and couldn't get anything.

  Frustrated, I pulled that rag-tag network of ground clips off the whole thing, and I guess you know what happened.

  The scrolling noise wave went away.

  So, I don't know what's the major thing to look for with the good solid ground connections. Is it to make sure the center tap on the monitor AC input is at the same potential as the signal ground for the video signals? I never did try to try adding back the alligator clips to find out where the noise got introduced, but I suspect in a normal cabinet setup, it would point to an insufficient ground strap between two or more sub-assemblies.

  My cockpit still has a wave to it's monitor, but it has some ground wires between components too.
  Trying to avoid ripple can drive people nuts...

  I do understand that you can get ground loops in equipment and that is why high-end test equipment is designed with a single ground for signal and a separate one for power - so try not to combine these and see what happens.

  John :-#)#

  Good luck.

---- William Boucher <boucher@mnsi.net> wrote:
  Thank you John for your reply. You are always keen to help out and it is much appreciated. Thanks for the links and tips. I have been through the very useful faq in detail many times and I have taken its recommendations to heart. I did indeed install the extra grounding wires between the supply and the monitor and the game boards. I am using the original supply but I have yet to re-cap it, although I plan to do that very soon. I'm hoping that will solve the jitter problem. As far as I can comprehend, I have installed every upgrade known to mankind with respect to the monitor. I also have strapped the transformer to run the system at a slightly lower voltage.

William Boucher

  ----- Original Message -----
  From: John Robertson
  To: vectorlist@vectorlist.org
  Sent: Thursday, November 26, 2009 11:58 AM
  Subject: Re: VECTOR: Star Trek pic waving?

  William Boucher wrote:
    Just wondering if any Sega Star Trek experts out there might know what is causing my GO8-003 monitor to show a very slow kind of a jittery wave. The wave travels from right to left and also bottom to top about once per 5 seconds. The vectors are all correct and are nice and bright. The wave is not an absence of lines but is a shaking of them. The shaking tends to be only within about a 1 inch wide swath at a time. Vectors in other areas are rock steady. For example, when the 3D area is showing a green station, the lines separate from each other by about 1/8" as the wave passes by. The game is totally playable and the sounds are good.

    I just recently rebuilt the entire monitor, all new caps, diodes, transistors, many resistors, and all new headers and sockets and trifurcon wire terminals.
    My parts list for the monitor is available here: http://www.biltronix.com/arcade_electcomp_01.html#GO8_parts

    I have just today generated a Digikey order of components so that I can renovate the power supply. At present, it is not yet restored but all the outputs are bang on. I haven't checked the outputs for ripple yet (say due to bad caps).

    Anyways, just wondering if anyone has seen this problem before and knows the root cause and would care to share their experience.

    Thanks in advance...

    William Boucher
  Have you upgraded the ground connections from the power supply to the logic boards and monitor? I assume you are using the original power supply and not a switching power supply.

  You will need to fix this or you run the risk of damaging the monitor if the ground reference shifts enough to bias the drive transistors enough to blow them.

  See page 36 of the Electrohome GO-8 FAQ covers the ground upgrades and reasons:
  http://arcarc.xmission.com/PDF_Monitors/FAQ%20Electrohome%20G08%20Version%200.8%20dated%2025%20Feb%2020.pdf

  And power supply upgrades from the Sega XY FAQ @
  http://www.mikesarcade.com/cgi-bin/spies.cgi?action=url&type=info&page=segaxyfaq1.6.txt

  ===========
  Power supply
  ============

  Sega/Gremlin power supplies are not the most reliable. If you have a dead one,
  you have a few choices: you can repair it, or replace it.

  In most cases repairing these power supplies is straight forward. If you open
  it up, you'll see there's really not much to it. The voltage regulators are
  all mounted and can be easily replaced.

  If you decide to modernize your game and put in a switching power supply, there
  are a few things to consider:

  1) The Sega/Gremlin power supply has a built in audio amplifier. You'll need
     to provide your own if you replace it. I've had good luck with using the
     Bally Midway Dual audio amps as a replacement, but any audio amp should do.
  2) You'll need a 3VAC supply for the power-on reset. I've heard that using
     +5VDC as a substitution may work, but your milliage may vary.
  3) You'll need +5VDC, -5VDC, +12VDC, and -12VDC. John Robertson says you
     may be able to get by with substituting -5VDC for the -12VDC for the video,
     but you'll need to adjust your picture.

  Or if you wish, you can use a switching power to supply the more common
  voltages and keep the old power supply in there and use it for the things that
  may still work (audio amp, 3VAC, -12VDC). Just make sure if you do this to
  make the grounds common between the two power supplies.

  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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-- 
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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