Appendix A: Common Ground Connections - Vector G08 Series Faq

G08 Vector Monitor Guide

Appendix A: Common Ground Connections

From: John Robertson <jrr@flippers.com>
Newsgroups: rec.games.video.arcade.collecting
Subject: TechTIP: How to make VECTOR MONITORS very RELIABLE!
Date: 22 Oct 2001
It's been a little while since my last Tech Tip, but this i s something that's been on my mind for a
while now, and a posting in the Vector mail-list got the following response from me...:
Vector monitors blow up because the ground reference for the monitor drifts relative to the logic
boards (MPU and video) when the power supply connections overheat. This will then bias the input
signals offset enough to overdrive the outputs. Hence my argument for chucking the original power
supply and putting in a switching supply. I started doing that about ten years ago and have not lost
a single Electrohome/Sega monitor since. I assume this also kills Tempest/Star Wars/Major
Havoc/... monitors etc. Those pesky grounds get a few ohms resistance and all sorts of nasty things
happen.
I first discovered this on Gottlieb pinballs over ten years ago-the ground for the regulator would
overheat the pin/wiper contact which would become a small resistor and thus the ground of the
MPU would drift up relative to the cabinet ground, which also happened to be the ground path for
the driver transistors. When the MPU ground would change to about 0.5 to 0.7VDC above cabinet
ground the base of the transistors would then start to conduct as the MPU would be trying to turn
off the transistors, but the Emitters are tied to the cabinet ground. Hence the transistors would start
to conduct... You will recall that transistors generate far more heat when they are used at the
beginning of their working range rather when they are switched completely on and off as in regular
vector monitors (or solenoid drivers, etc.). So in a little while, it croaks. No obvious cause...replace
the transistors and everything works. For now...
So get VERY GOOD GROUND (COMMON) CONNECTIONS BETWEEN THE MONITOR,
MPU AND POWER SUPPLY for reliability!!!!!!!!!!!!!!!!!!!!!!!! Solder fat conductors with nasty
heavy gauge connectors between each component in the system. Put in healthy SWITCHING
SUPPLIES!
Happy vectors will result.
John :-#)#
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