Electrohome G08 Manual

							G08 Vector Monitor FAQ & Guide Page 31 of 39   USING A G08-003 WITH COSMIC CHASM  
Cosmic Chasm uses the G08-105 monitor, which takes slightly different inputs and is basically a 
better version monitor than the G08-003. It is, however, hard as hell to find the G08-105 monitor.  
If you have a Cosmic Chasm game or boardset and it is missing this monitor, there is hope. 
 
The G08-003 can be substituted in place of the G08-105 (as can the WG6400 monitor, but that is 
an equally difficult monitor to find). To use the G08-003 with Cosmic Chasm, read the following 
from David Fish: 
 
“As per the request of several V-List members here is the instructions for reworking a 
Cinematronics Cosmic Chasm boardset to work with a standard G08-003 monitor. While the 
procedure will correct the color intensity problems it does nothing to help the [relatively] crappy 
slew rate of the G08-003, you’re on your own there. 
 
This modification is used to adjust the color signal (R, G & B) levels of a Cosmic Chasm board so 
that they are compatible with a standard Electrohome G08-003. When a Cosmic Chasm boardset is 
run using a G08-003 there will be visible black level or return-to-origin lines on the screen. The 
origin points will also be visible and will burn several small holes in the phosphor relatively 
quickly. The problem occurs because the Cosmic Chasm RGB outputs are designed to be 
compatible with a Wells-Gardner 19K6401 or Electrohome G08-105 which are 1V (BLACK level) 
to 3.6V-4.0V (full ON). The color levels of the more common Wells-Gardner 19K6101 are similar. 
Why Electrohome chose 0-4V is anyones guess. 
 
To correct this, the gain and offset of the RGB signals must be modified. The mod is fairly simple 
and reversible in case you ever get your hands on the correct monitor. It requires 6 resistors, three 
potentiometers and some soldering skill.  
 
Components required: 
· QTY 3 15.4K 1% metal film resistor 
· QTY 3 90.1K 1% metal film resistor 
· QTY 3 25K potentiometer, Bourns P/N 3266W-1-253  (Digi-Key P/N 3266W-253-ND)  
 
Modification Instructions:  
 
1) Carefully remove the three 9.1K resistors R1, R9 and R17 from the Cosmic Chasm Game 
Processor PCB. I suggest the following method: cut one leg of the resistor right at the body 
and bend both the resistor and the cut lead vertical. Heat the solder fillet on the trace side 
and pull the resistor/lead out the component side. Use a solder sucker to remove the leftover 
solder.  
2) Install the 15.4K resistors in the R1, R9 and R17 locations.  
3) Using a non-permanent adhesive (rubber cement or similar) attach a 25K potentiometer to 
the top of IC U29, U14 and U15. Orient the pots so that the pots #1 lead is right above and 
close as possible to the ICs pin #7 (+15V) and the adjustment screw is on the side with pins 
1 thru 4. Let the glue set.  
4) For each pot bend the #1 lead down and solder to the ICs pin #7.   
						

							G08 Vector Monitor FAQ & Guide Page 32 of 39  5) Using a short piece of wire-wrap wire connect the each pots #3 lead to the ICs #4 pin (-
15V).  
6) Connect a 90.1K resistor between pin #2 of the IC and #2 lead of the pot for each.  
 
Power up the boardset. Connect a scope to the RED color output on connector P2 pin 6. Note: all 
ODD numbered pins are GND. Adjust the pot attached to U29 so that the signal level swings 
between 0 volts and 4 volts. Repeat the adjustment for GREEN (U14) and BLUE (U15).  
 
* Modification complete *  
 
CAVEAT! - I have done this modification to two boardsets so far and got the expected results. 
However, since electronics is three parts Black Magic, two parts blood sacrifice and one part skill, I 
cannot take responsibility for what occurs to your board should you make this modification. All I 
can say is It worked for me’.” 
  
						

							G08 Vector Monitor FAQ & Guide Page 33 of 39   Appendix A: Parts Lists  
 
The Input Clamp Board is only discussed in the Preliminary G08-003/004 Service Manual. 
Included below is the parts list. Not all of these parts are necessary for a monitor rebuild, but are 
good to have on hand. 
 
Input Clamp Assembly Parts List Location Part Description Upgrade Notes D800 1N914   D801 1N914   D802 1N914   D803 1N914   D804 1N914   D805 1N914   D806 1N914   D808 1N914   Q800 2N3904   Q801 2N3906   Q802 2N3904   Q803 2N3906   R800 10K ¼W Resistor   R801 4.7K ¼W Resistor   R802 4.7K ¼W Resistor   R803 10K ¼W Resistor   R804 10K ¼W Resistor   R805 4.7K ¼W Resistor   R806 4.7K ¼W Resistor   R807 10K ¼W Resistor   R809 1K ¼W Resistor   C800 10 uF 16V Radial Capacitor   C801 10 uF 16V Radial Capacitor   C802 10 uF 16V Radial Capacitor   C803 10 uF 16V Radial Capacitor    
  
						

							G08 Vector Monitor FAQ & Guide Page 34 of 39    
The Current Limiter boards are attached to the deflection board and are only discussed in the 
Preliminary G08-003/004 Service Manual. Included below is the parts list. Not all of these parts are 
necessary for a monitor rebuild, but are good to have on hand. 
 
Horizontal Current Limiter Vertical Current Limiter Location Description Location Description D200 1N914 D250 1N914 D201 1N914 D251 1N914 D202 1N4935 D252 1N4935 D203 1N4935 D253 1N4935 Q201 2N3906 Q251 2N3906 Q202 2N3904 Q252 2N3904 R200 100-Ohm 0.25W Resistor R250 100-Ohm 0.25W Resistor R201 100-Ohm 0.25W Resistor R251 100-Ohm 0.25W Resistor R202 0.15-Ohm 2W Resistor R252 0.15-Ohm 2W Resistor R203 0.15-Ohm 2W Resistor R253 0.15-Ohm 2W Resistor C201 0.1mF 200V capacitor C251 0.1mF 200V capacitor  
  
						

							G08 Vector Monitor FAQ & Guide Page 35 of 39   Appendix B: G08 SYSTEM REDESIGN  
 
Taken from a Sega/Gremlin Service letter: 
 
Gremlin/Sega reports that all of the problems encountered with the industrys first color X-Y game 
Space Fury have been identified and solved. 
 
The problems are centered around the deflection (X-Y) amps. Underrated power transistors 
combined with an extended on time during the power-up routine resulted in damaging the 
amplifier circuit. 
 
The remedy includes a modification to the card cage and replacement of the Electrohome Monitor 
with a redesigned unit. 
 
Gremlin/Sega will have replaced all defective monitors and modified all game card cages by the 
end of October. 
 
Initial field fixes did not resolve the problem entirely and Gremlin/Sega decided to undertake the 
monitor replacement program. 
 
Electrohome, the monitor manufacturer, will replace monitors in the Eastern U.S., while 
Gremlin/Sega will handle the Western US. 
 
For further details contact your distributor.  
 
  
						

							G08 Vector Monitor FAQ & Guide Page 36 of 39   Appendix C: Common Ground Connections  
 
From: John Robertson  
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 is 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 :-#)# 
 
  
						

							G08 Vector Monitor FAQ & Guide Page 37 of 39   Appendix D: Testing Transistors  
 
Most of the failures in the Electrohome G08 monitor (as is the case with most electronic devices) 
are semiconductor failures, specifically, the transistors. All transistors discussed in this document 
can be tested in the same way; it does not matter if they are the large chassis-mounted transistors or 
the tiny PCB-mounted transistors. With the transistors out of circuit, set your multi-meter on Rx1K 
scale and use the following procedures. 
 
NOTE: ANALOG AND DIGITAL MULTI-METERS REQUIRE DIFFERENT TESTING 
PROCEDURES FOR TRANSISTORS! Digital meters always show infinite resistance for all 6 
combinations (if you accidentally get your skin involved it will show something around 2M Ohms). 
The best way to test transistors with a DMM is to make use of the diode test function, which will 
be described after the analog test. For both methods, if you read a short circuit (0 Ohms or voltage 
drop of 0) or the transistor fails any of the readings, it is bad and must be replaced. 
 
Why do Digital Voltmeters read open circuits on diodes and transistors? 
 
Because of the ability to use amplifiers, DVM can use much smaller voltages to check resistance. 
For the most part this is a good thing. It allows you to check resistors in circuit, without turning on 
things, like transistors. 
 
Diode junctions (which there are two of in a transistor) do not “turn on” until they reach 
somewhere around 0.4 ~ 0.7 volts, depending upon what they are made of, and a lot of other stuff. 
In a way, diode junctions are similar to neon light bulbs, they act like open circuits until the right 
voltage is reached, and then they act like shorts, until the voltage drops below the critical threshold. 
Without proper current limiting, the diode junctions explode. The thing about diodes is that they 
only do this in one direction, if you switch the test leads, they do not conduct at all. (Well, until the 
voltage gets much higher, and then it is a bad thing. ;^) 
 
Sometimes you want to be able to “turn on” the diode junctions (to test them), so DVMs have a 
“Diode” test mode. This places enough voltage on the test leads to turn on the diode junction. The 
number you read on most meters is the actual turn on voltage threshold across the diode. 
 TESTING TRANSISTORS WITH AN ANALOG OHMMETER 
 
For type NPN transistors, lead A is black and lead B is red; for type PNP transistors, lead A 
is red and lead B is black (NOTE: this is the standard polarity for resistance but many multi-
meters have the colors reversed; if the readings do not jive this way, switch the leads and try it 
again). Start with lead A of your multi-meter on the base and lead B on the emitter. You should 
get a reading of 2.5K Ohms. Now move lead B to the collector. You should get the same reading. 
Now try the other 4 combinations and you should get a reading of infinite Ohms (open circuit). If 
any of these resistances is wrong, replace the transistor. Only 2 of the 6 possible combinations 
should show a resistance and that value should be 2.5K Ohms; none of the resistances should be 0 
Ohms (shorted).  
						

							G08 Vector Monitor FAQ & Guide Page 38 of 39    TESTING TRANSISTORS WITH A DIGITAL MULTI-METER 
 
Set your meter to the diode test. Connect the red meter lead to the base of the transistor. Connect 
the black meter lead to the emitter. A good NPN transistor will read a JUNCTION DROP voltage 
of between 0.45v and 0.9v. A good PNP transistor will read OPEN. Leave the red meter lead on the 
base and move the black lead to the collector. The reading should be the same as the previous test. 
Reverse the meter leads in your hands and repeat the test. This time, connect the black meter lead 
to the base of the transistor. Connect the red meter lead to the emitter. A good PNP transistor will 
read a JUNCTION DROP voltage of between 0.45v and 0.9v. A good NPN transistor will read 
OPEN. Leave the black meter lead on the base and move the red lead to the collector. The reading 
should be the same as the previous test. Place one meter lead on the collector, the other on the 
emitter. The meter should read OPEN. Reverse your meter leads. The meter should read OPEN. 
This is the same for both NPN and PNP transistors. Thanks to Randy Fromm 
 for this excellent summary of the diode test method. 
 
 
  
						

							G08 Vector Monitor FAQ & Guide Page 39 of 39   REFERENCES  
 
1. The Wiretap Arcade Game Collectors Archive - http://www.spies.com/arcade/ 
Contains information about G-08 system games, as well as schematics for the monitor and game 
boards. 
 
2. Tac/Scan, Zektor, or Star Trek manual 
These manuals contain the most up-to-date information on the Electrohome G08-003 model 
monitor. 
 
3. Sega-to-Atari color XY circuit 
If you have given up on the G08, this is an alternative solution. 
 
4. Sega/Gremlin Color X-Y manual – www.arcademonitors.com 
Contains schematics for G08-001, future G08-003 
 
5. Preliminary Service Data G08-003/004 X-Y Color monitor – www.arcademonitors.com 
 
 
DOCUMENT HISTORY  
 
Version 0.1: Looking for contributors 
Version 0.2: David Shumans additions 
Version 0.3: Michael Kelleys additions 
Version 0.4: Updated cocktail and Cosmic Chasm Information 
Version 0.5: Additional tips added 
Version 0.6: Added more info about neck tube swap 
Version 0.7: Major revision. Added more info about G08-105 
Version 0.8: Major revision. Reformatting and additional info on cap kit, parts, power supply 
 
 
END