Electrohome G08 Manual

							Page 1 of 39  The Evil, Infamous, Unreliable, Flaming... 
Electrohome 
 
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FAQ version 0.8 
February 25, 2002 
 
 
 
 
Table of Contents 
 
INTRODUCTION..............................................................................................................................2 
MONITOR HISTORY........................................................................................................................3 
PART DESCRIPTIONS.....................................................................................................................5 
HOW IT ALL WORKS....................................................................................................................14 
REPAIR PREPARATION................................................................................................................15 
DEBUGGING THE MONITOR......................................................................................................19 
INSTALLING A CAP KIT..............................................................................................................23 
MAKING THE MONITOR MORE RELIABLE.............................................................................28 
TUBE REPLACEMENT..................................................................................................................30 
USING A G08-003 WITH COSMIC CHASM................................................................................31 
Appendix A: Parts Lists....................................................................................................................33 
Appendix C: Common Ground Connections....................................................................................36 
Appendix D: Testing Transistors......................................................................................................37 
REFERENCES.................................................................................................................................39 
DOCUMENT HISTORY..................................................................................................................39 
 
 
 
CAUTION: The Electrohome G08 monitor is extremely flammable. Do not operate around combustible liquids or materials. This document should not be used to put out any flames caused by the monitor.  
						

							G08 Vector Monitor FAQ & Guide Page 2 of 39    
INTRODUCTION   
Ok, enough making fun of the G08 :-). It is actually a pretty strong monitor considering the work 
that it does, and when it is working it is a fairly impressive color vector monitor. There are horror 
stories about this monitor, and most of them are true (and the list is long), but on the other hand, 
there are others have had theirs for 15 years without it breaking down once. Before working on 
your G08 monitor, read through this entire document, and be certain you have schematics for 
additional review. 
 
 
Acknowledgements 
 
The following people have contributed to the development of this document: Mark Jenison; David 
Shuman; Michael Kelley; Al Kossow; Roger Boots; Zonn Moore and David Fish. 
 
 
 DISCLAIMER  CAUTION!!! LETHAL VOLTAGES ARE PRESENT IN ARCADE MONITORS. SUITABLE PRECAUTIONS SHOULD BE TAKEN BEFORE ATTEMPTING TO SERVICE YOUR MONITOR. REMEMBER, NO WARRANTIES, EXPRESS OR IMPLIED, ARE GIVEN. USE THIS INFORMATION AT YOUR OWN RISK. I AM NOT RESPONSIBLE FOR ANY DAMAGES THAT MAY OCCUR TO YOUR PERSON OR PROPERTY.   
 
 
The Electrohome G08 is the monitor that was used in the Sega/Gremlin color vector games Space 
Fury, Eliminator, Zektor, Tac/Scan, and Star Trek and in the Cinematronics game Cosmic Chasm. 
The Electrohome G08 monitors, like other vector monitors, were notorious for their failure rate.  
There were a few different versions of the G08 monitor in an attempt to evolve towards a more 
reliable design. 
 
The first model of the Electrohome G08 monitor was the G08-001. Since Space Fury was 
Sega/Gremlins first color vector release, one might find this monitor in an early production Space 
Fury. The monitor, however, must have been very prone to failure, as in the initial manual there 
already was a “future” version already being worked on. The G08-001 monitor used MJ15003 and 
MJ15004 deflection transistors and had direct connections from the deflection transistors to the 
deflection board. Sega determined that the problems encountered with the G08-001 were centered 
around the deflection amplifiers. Underrated power transistors combined with an extended on 
time during the power-up routine resulted in damage to the amplifier circuit. 
  
						

							G08 Vector Monitor FAQ & Guide Page 3 of 39   The second model was the G08-003 (there does not seem to be a G08-002). The most notable 
change in the G08-003 was the addition of two “current limiting” boards that are plugged in 
between the deflection board and the heatsink mounted deflection transistors. These boards provide 
current limiting and short circuit protection for the deflection transistors. All four deflection 
transistors were upgraded to 2N6259 transistors, and a HV regulator board was added to the HV 
unit. 
 
However, Electrohome confused the issue of the G08-003 by releasing several different deflection 
board revisions under the same model number. These different “issues” are covered in the 
deflection board section of this document. 
 
The third model of the monitor was the Electrohome G08-004. The preliminary manual, though it 
includes the G08-004 in the title, does not mention the G08-004, nor does it provide schematics. It 
is thought that the G08-004 is the monitor model used in the cocktail versions of the Sega XY 
games, meaning it is nothing more than a G08-003 mounted on a different frame. Whether or not 
the G08-004 is another version of the deflection board or just a monitor frame change is still a 
mystery. 
 
According to the manual, Cinematronics’ Cosmic Chasm uses still another version of the monitor 
called the G08-105. There has been some speculation that Electrohome made this version of the 
monitor specifically for Cinematronics. The G08-105 was manufactured in October of 1982, and it 
uses SDT 1064’s for deflection transistors. A special transformer(s) used for this game outputs 
49VAC from the center tap. On this version, the current limiting boards are removed, and their 
circuitry has been integrated into the deflection board. Also, the monitor expects inputs in the 
1VDC to 4VDC range, whereas the other versions of the G08 expect inputs in the 0VDC (off) to 
4VDC range (full brightness). The G08-105 also uses a Rauland medium resolution tube, 
19VNJP22, and a different deflection yoke than the standard G08. Unfortunately, there is very little 
information known about this monitor. 
 
This document mostly covers the Electrohome G08-003 model, since it is the most common of the 
monitor versions, and experience with the other versions of the monitor is limited. This document 
will discuss the parts of the Electrohome G08-003 monitor and the symptoms and testing 
procedures of the entire set up. Hopefully this document will assist in the repair and debugging of 
this monitor. But first, a little background into the history of the Electrohome G08 monitor. 
 
 
MONITOR HISTORY  
 
The following information is a compilation of conversations, e-mails, and chats between Michael 
Kelley and Don Mahler, a Sega/Gremlin designer who worked on many of the vector games that 
used the Electrohome GO8.  
 
Don started at Sega/Gremlin in May 1981, while he was on recess from Cal Poly for the summer. 
He was hired initially to help design the Vector control and timing boards that are in the G-80 
boardsets.  
						

							G08 Vector Monitor FAQ & Guide Page 4 of 39    
“At the time I came to work at Sega, the G-80 setup was already there. I think Astro Blaster was 
one of the first to use the configuration. For the time it was pretty impressive. The modular design 
got some things done that would have been very difficult to do on a single board. The main CPU 
was not being taxed with sound/speech operations, so the speech was excellent for that time, and 
the sounds were nice, too.  
 
They had already begun working on a game that they wanted to be vector, and decided they wanted 
it to be color as well. Initially, it reminded me of a vector version of Gorf, with the player being 
taunted by a weird alien during the game. None of the color routine was set up yet, (I think we were 
running a G05), and the game didn’t look very much like the final product at all. This game ended 
up being Space Fury. 
 
I was brought in after I spoke with an Electrohome representative who was lecturing at Cal [Poly]. 
He told me that they were working on a color Vector monitor, and since I was (and always have 
been) interested in games, he suggested that I apply to Sega/Gremlin on a co-op for summer work. 
I ended up working there for almost 3 years.” 
 
“My job was to take the rough breadboard they had as a AVG and design something that would fit 
into the G-80 setup (this was a must, they were really in love with it) and eliminate the massive 
board they were using in the lab. I was initially going to try to do this on one board. But, after about 
3 weeks into it, I decided that it would be impossible to do one board that would fit into the G-80 
cage. So, I came up with the idea of both the vector timing and control boards, and it ended up 
working out.” 
 
“When I heard of the problems that plagued the monitor, I felt terrible. We at Sega (and 
Electrohome) really wanted a spot killer, but at the time, Atari sued whomever they wanted, and 
always won. The G05 design (Asteroids, Asteroids Deluxe, Battlezone, Red Baron, Bally’s Omega 
Race, etc.) was actually developed by Atari. Atari’s production was not geared to making monitors, 
so they commissioned Electrohome to produce the monitor (Atari actually received a cut for Bally 
using the G05 in Omega Race). So, using a spot killer was definitely out, and Electrohome had to 
come up with something else. Many aspects of the monitor and x/y timing and control boards were 
developed so that we wouldn’t get crushed by Atari’s legal dept...” 
 
“I remember Mark Shayton (Sega/Gremlin head of engineering) having a fit over the G08’s 
problems. Initially, they pointed the finger at me (I was the dumb intern, I made the x/y 
timing/control boards), but things got pretty hot (no pun intended) between Sega and Electrohome 
when it was proven that the monitor was the problem...”  
						

							G08 Vector Monitor FAQ & Guide Page 5 of 39   PART DESCRIPTIONS  
 
The following sections describe the different major assemblies of the Electrohome G08-003 vector 
monitor. Before we delve into the different parts of the G08 monitor, it is important to discuss the 
different schematics that exist. The best schematics to reference are included in the Tac/Scan, 
Zektor or Star Trek manuals (these three manuals, aside form a couple of minor formatting 
changes, are cut-and-paste the same). These manuals contain the schematics with the HV Regulator 
PCB, the Input Clamp board and the Current Limiting boards. From review, it appears Electrohome 
made updates to the G08 monitor, but Sega neglected to change this information in their manuals. 
 
Below is a brief summary of the different manuals and their attributes. I have given some 
descriptions an “a”, “b”, or “c” designation. The “a” signifies the inclusion of the HV Regulator 
board only, while the “b” suffix includes both the HV Regulator board and the Input Clamp board. 
The “c” denotes the most complete information on the G08-003 monitor. Unfortunately, there are 
no schematics for the “c” monitor. 
 
 
 
Manual  
Schematics  
Parts List Sega 
Drawing Number Deflection Board 
Diagram Space Fury Preliminary none none none none Eliminator Upright none none 200-0025 none Tac/Scan G08-003c G08-003b 200-0025 Issue 1 Zektor G08-003c G08-003b 200-0025 Issue 1 Star Trek Upright G08-003c G08-003b 200-0025 Issue 1     G08 Service Manual G08-001; G08-003a G08-001 none Issue 1 G08-003/004 Preliminary 
Service Manual G08-003b G08-003c none none  
 
 
Input Clamp Board  
This small 1½” x 3” board is usually mounted on a thin metal support across the back chassis of the 
monitor. This board prevents invalid inputs from overdriving the monitor. Without this board, the 
monitor picture will be too large, so the board does some “trimming down” of the signal inputs. 
 
The input clamp board is the first interface into the monitor, and plugs into the main deflection 
board. Since it is screwed to a thin piece of metal, usually you will find non-conductive tape on the 
back of this board to prevent the header pins from grounding to the metal. A detailed parts list of 
the Input Clamp board is provided in Appendix A. 
  
						

							G08 Vector Monitor FAQ & Guide Page 6 of 39   The Input Clamp board has a pinout as follows: 
 
Pin # Description Specification 1 Horizontal Input +/- 4V maximum 2 Vertical Input +/- 3V maximum 3 Common Ground 4 Red Input +4V @ full brightness 5 Green Input +4V @ full brightness 6 Blue Input +4V @ full brightness  
 
Deflection Board  
The deflection board is the large PCB mounted to the bottom of the chassis (7” x 10”). The G08-
003 version will also have two vertically mounted PCBs (2” x 2”) connected to the deflection board 
which mount on the header pins on the right side of the board. These are the “current limiting” 
boards. According to the schematics, the G08-001 does not have the “current limiting” boards, nor 
the header pins on the deflection board. Therefore, the deflection transistors would plug in directly 
to the G08-001 deflection board. 
 
The horizontal and vertical current limiting boards were an attempt to add short circuit and current 
limiting protection for the output transistors. These boards would typically fail catastrophically in 
the event that something went wrong with the deflection circuitry. Unfortunately, there are no 
official schematics for the current limiting boards. 
 
The deflection board creates a low voltage power supply for the HV board, and controls the “X” 
and “Y” video amplifiers. Looking at the board with the potentiometers (controls) towards you, the 
upper right side of the board is “Y” deflection circuitry, the lower right/middle is the “X” 
deflection circuitry, and the left side of the board is the low voltage power supply. 
 
There are several different versions of the deflection board that were made for the G08-003. They 
are easily distinguished from one another by looking at the top of the deflection board under the 
large 3-ohm 20W ceramic resistors and looking for text stating “Issue X Component Layout”, 
where “X” is the issue number. 
 
Issue 1, 2, and 3 deflection boards have the same or similar component layouts as found in the 
“Sega/Gremlin” Color X-Y monitor manual. Issue 1, 2 and 3 deflection boards have resistors R636, 
R637, R736, and R737 typically on the bottom of the deflection board, or hacked into the current 
limiting boards. 
 
Issue 4 deflection boards may or may not exist. It is currently unknown if any G08 Issue 4 
deflection boards were produced. 
  
						

							G08 Vector Monitor FAQ & Guide Page 7 of 39   Issue 5 deflection boards have places for resistors R636, R637, R736, R737 screened on top of the 
board. Issue 5 deflection boards may be found with or without diodes D601, D602, D701, and 
D702 populated. If your deflection board has these diodes, just leave them installed. They do not 
appear to make a functional difference. 
 
There are even different issue numbers for the foil patterns screened on the bottom of the deflection 
boards. These issue numbers on the bottom of the deflection boards do not necessarily match the 
issue number on the top of the board. For example, you might find an issue 2 screen on a issue 3 
deflection board, or issue 4 screen on an issue 5 deflection board. 
 
All these different variations make it very difficult to write a document for a very specific 
deflection board. While one deflection PCB may look much different than another physically, most 
of the time one will find the components mounted or soldered somewhere else which makes the 
two boards functionally equivalent. 
 
The schematics found in the Tac/Scan, Zektor and Star Trek manuals matches the schematics found 
in the “Preliminary service data for the G08-003/004 X-Y color monitor (up to date as of Feb 
1982)”. Neither the schematics nor the parts list show diodes D601, D602, D701, or D702. For the 
most part, it appears that all issues of the G08-003 deflection board are attempts to hack (and 
probably should be hacked) to support the G08-003/004 schematics in general. 
 
I would not recommend modifying any G08 deflection board from issue to issue, but to simply 
verify that the current hacks on the board match the schematics in the Tac/Scan, Zektor or Star 
Trek manuals.  If they do not, modify the deflection board accordingly. 
 
The input amplifier, IC600, and surrounding circuitry on the deflection board serve two purposes: 
First, it compensates for a type of distortion known as the pincushion effect. This occurs because 
the electron-beam must travel a greater distance when striking the edges of the CRT than when it 
hits the center. If we cause the beam to trace along the edges of the CRT, the beam would draw a 
box with its left and right sides bowed inward. To compensate for the effect, this circuit offsets the 
point where the beam would normally strike the CRT surface. 
 
Secondly, this circuit contains two error amplifiers, one for the horizontal and one for the vertical 
inputs. Each error amp has two inputs; one is set to zero volts, the other accepts the analog signal 
from the G-80 system, sensing current movement in the deflection coil. The analog signal is 
allowed to pass through the error amps and drive the deflection (power) amps. The outputs of the 
“X” and “Y” power amps pass current through their respective deflection coils. The output leads of 
the two coils are connected back to the analog inputs of the respective error amps, as mentioned 
above. This acts as an error, or feedback, signal and ensures that the current through the deflection 
coil remains proportional to the voltage on the error amp inputs. If this signal were not provided, 
there would be a slight deflection error when an analog input signal was present. 
 
IC600 is a custom chip, Electrohome part number 14-002156-01 (and Sega part number 315-0117). 
This IC can be destroyed in certain failure modes, and since it is custom, the only way to repair a 
deflection board that has a bad or missing chip is to find another deflection board. 
  
						

							G08 Vector Monitor FAQ & Guide Page 8 of 39   The circuit of D409, R410, and R411, in combination with IC900 on the HV board, is a spot-killer 
that prevents the electron-beams from burning a hole in the phosphor surface of the CRT when the 
monitor is turned off. 
 
The outputs of the “X” and “Y” deflection amps can swing between +60V and -60V. This voltage 
is high enough to provide up to 8 amps, peak-to-peak, of current through the deflection coils. The 
power input of the deflection board is an isolated +45V Center Tap. 
 
Pin # Connection 1 +45 VAC 2 Center Tap 3 +45 VAC  
One of the most important things to watch on these monitors is the input power. Input voltage is 91 
VAC nominal. You are better off running lower than higher. Lower power will reduce writing 
speed.  Higher power blows output transistors. 
 
The low voltage power supply section creates the following voltages: 
 
· +/-63 VDC (goes to X-Y power amplifiers) 
· +55 VDC to RGB video drivers and spot killer 
· +/-9.1 VDC to the IC’s 
· +126 VDC to the EHT oscillator 
 
 
 
When you look at your deflection board and your schematics, you may notice some discrepancies 
and ask Where is part x? 
 
· R636, R637, R736, and R737: On issues 1, 2 and 3 deflection boards, these resistors should 
be found on the bottom of the deflection PCB. 
 
· C726: The capacitor C726 is typically found in parallel across R726 (either over the resistor 
itself, or soldered to the bottom of the board).  C626 is attached in the same manner. 
 
· Diode near R726: Sometimes there is no diode near R726. The diode is a 1N914.  If you 
want to insert the diode, simply place the board in a position where the current limiting 
boards are on your left. Lift the right leg of the resistor, and attach the banded end of the 
diode away from the resistor, and place the end of the diode in the hole the resistor leg was 
in. 
 
· D701, D702, D601, D602: These diodes are a bit of a mystery.  They originally appeared in 
the G08-001 and G08-003 schematics in the “Sega/Gremlin Color X-Y Monitor” manual, 
but then dropped out of the “Preliminary Service Data G08-003/004 X-Y Color Monitor”  
						

							G08 Vector Monitor FAQ & Guide Page 9 of 39  manual’s parts list and schematics.  However, they came back in the parts list for Tac/Scan, 
Zektor and Star Trek. 
 
· R635 and R735: Some G08 deflection boards have a ‘teepee’ of resistors in these locations. 
As noted in the schematics, there should be a single 3-Ohm 20W resistor in each location. 
Some have been replaced with two 1.5-Ohm resistors teepeed together. It is unclear why 
this modification was done to some G08-003 deflection boards. 
 
· Two resistors hacked onto the back of the current limiting boards: These resistors appear on 
Issue 2 and Issue 3 deflection boards for the most part. On both of the current limiting 
boards, the trace for pin 1 is cut near the top connector and a 0.2-Ohm 5W resistor it 
inserted (i.e., the traces are cut and hooked back together via the resistor). The trace for Pin 
2 of the connector is also cut near the top, and a 100-Ohm resistor goes from pin 2 to the 
BOTTOM CONNECTOR *pin1* (connecting with the other end of the 0.2-Ohm resistor).  
Pin 2 (top) is then jumpered down to the collector of Q704. These resistors are in the 
transistor #1 circuit. On issue 5 deflection boards, you will find these resistors missing, but 
there will be 100-ohm resistors on the deflection transistor harness across the terminals of 
transistor #1. 
 
This resistor ‘hack’ is detailed from an Issue 2 deflection board with an issue 2 screen on 
the bottom, and no cut traces on the bottom of the PCB as usually seen on most deflection 
boards. I think when this hack is used, the bottom of the PCBs did not have to be cut. 
 
 
 
Defection Transistors And Heat Sink  
When looking at the back of the monitor, the deflection transistors and associated heatsink is on the 
right, mounted to the metal frame. This metal box is a heat sink that holds two pairs of deflection 
transistors mounted on opposite sides. A cooling fan is mounted such that it blows air into the heat 
sink. The function of this part is to provide cooling of the deflection transistors. 
 
The deflection transistors for the G08-001 are listed in the schematics as MJ15003 and MJ15004. 
These transistors were replaced with the more heavy-duty 2N6529 transistors in the G08-003 
model. Unfortunately, the 2N6529 transistors have been discontinued, making these beasts difficult 
to find.  
 
If you are working on a G08-001 monitor, be VERY careful. The original G08-001 design used the 
MJ15003/MJ15004 in a push-pull combination - one NPN and one PNP. The later models of the 
G08 used the 2N6259 design where BOTH outputs were NPN. The driver circuit is quite different 
between the two models. Be certain you know which monitor you are working on! 
 
Rodger Boots had the following to say about the 2N6259 transistors: 
 
“There is nothing wrong with the 2N6259 and you are going to be hard pressed to find a better part. 
Just because the NTE388 LOOKS to be a better part doesn’t tell the whole story. There is not much  
						

							G08 Vector Monitor FAQ & Guide Page 10 of 39   out there that has better secondary breakdown characteristics than a 2N6259, but you will never tell 
that by looking at just numbers, you need to see a breakdown chart. This will show you where 
secondary breakdown is. 
 
For example, looking at the 2N3716 data sheet you will see that at full voltage (80 volts) the part 
will withstand 0.2 amps. That is only 16 watts allowed for what is supposed to be a 150-watt part! 
Compare that with a 2N6259 that can take 200 watts of dissipation with 90 volts across the part! 
 
It is about a 200-watt part and you can dissipate ALL OF IT with 90 volts across the part!!! A 
normal transistor would go into secondary breakdown (definition: localized melting of the junction 
due to current hogging - very destructive) at 20 to 40 volts. There are VERY few transistors that 
even come close to what this thing can do. 
 
What kills the 2N6259 is over voltage, plain and simple. The part is rated for (I think) 125 volts, 
maybe as high as 150. However, the G08 uses +/-63 volts IDEALLY. So when the amplifier 
swings to the rail during a fast vector draw you have close to 125 volts. 
 
Remember I said IDEALLY? That is with the game plugged in to a 110-volt line, since that is what 
the Gremlin/Sega power transformer was designed for. Are there any of you with only 110 volts 
coming out of the wall? More like 120 to 130, isn’t it? THAT is why I keep saying the game needs 
to be re-strapped to match the power line. Either buck out the extra voltage with some filament 
transformers or whatever, but DO reduce the voltage. And what happens when the occasional 
power line spike comes along? The monitor blows up, that’s what. 
 
In my Showbiz Pizza days we used to use NTE388’s in an Eliminator at about $10 per part. They 
still blew up until one of the techs (not me) ran the power into the 110 and 240 taps of the game 
power transformer. The result was a 130 volt winding. The transistors quit blowing. It was just that 
simple.” 
 
On some deflection transistor harnesses, there might be a 100-Ohm resistor placed across the 
terminals of two of the deflection transistors. I have no idea what to say about this other than some 
do, some dont.  These resistors do not show up in the schematics, and I have no idea what effect 
these resistors have on the circuit. 
 
 
HV Unit  
The High Voltage (HV) unit creates the high voltage for the tube as well as the AC voltage for the 
CRT heater. The HV unit consists of a PCB mounted in a metal box. The PCB has a HV 
transformer mounted on it. A small PCB (1” x 2”) is mounted to the outside of the box; this PCB is 
the HV Regulator PCB. The HV is mounted in a metal frame and has a 10-pin header at the top. 
The deflection board plugs in here.