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.
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G08 Vector Monitor Guide
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.
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G08 Vector Monitor Guide
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.
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G08 Vector Monitor Guide
“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 G80
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...”
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G08 Vector Monitor Guide
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
di fferent schematics that exist. The best schematics to reference are included in the Tac/Scan,
Zektor or Star Trek manuals. These 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.
G08 Service Manual G08-001; G08-003a G08-001 none
G08-003/004 Preliminary Service Manual G08-003b G08-003c none
Input Clamp Board
This small 1 ½” 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.
Schematics
Parts List
Sega
Drawing Number
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G08 Vector Monitor Guide
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 G08003 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.
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 (or 2 1.5-ohm 20W resistors, depending on your deflection
board version) 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.
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G08 Vector Monitor Guide
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 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 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.
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G08 Vector Monitor Guide
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. If the input voltage is too high, the
rectified voltages for everything also increases, and overvoltage may cause problems for some
parts, especially the deflection 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, or possibly the current limiting boards.
• 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”
manual’s parts list and schematics. If they are missing, don’t bother installing them.
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G08 Vector Monitor Guide
• R635 and R735: Some G08 deflection boards have a ‘teepee’ of large ceramic 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 in series. It is unclear
why this modification was done to some G08-003 deflection boards (possibly cooling
reasons?).
• 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 is
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 “pin 1” (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
tran sistor #1 circuit. On issues 5 deflection boards, you will find thesse resistors missing,
but there will be 100-ohm resistors on the deflection board 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
out there that has better secondary breakdown characteristics than a 2N6259, but you will never tell
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G08 Vector Monitor Guide
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.”
There might be a 100-Ohm resistor placed across the terminals of the deflection transistors. I have
no idea what to say about this other than "some do, some don't". This resistor(s) 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.
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G08 Vector Monitor Guide
The pinouts for the HV 10-pin header are as follows:
The HV PCB has three controls on it: R917 (frequency control), R918, and R933 (sensing voltage).
Frequency control regulates the voltage the transformer puts out. Sensing voltage controls the level
at which the HV supply will shut itself off to prevent a dangerous, X-ray producing overvoltage
condition. R918 provides a sensitivity setting for shutting down the HV when the beam is not
changing. Some manuals incorrectly reference R933 as R920. R920 was the G08-001 name for
this control.
The large control on the HV unit (R922) is the focus control.
The small PCB affixed to the outside of the metal cage is a voltage regulator, which regulates the
input between +100VDC and +126VDC.
IC900 on the HV unit is a high-voltage oscillator. This is Electrohome part number 14-002155-01
(EHT Control Circuit), and is another custom Sega part (Sega Part number 315-0118). This IC
operates the high-voltage transformer, T901. This transformer is technically a flyback type, but it is
not used to deflect the beam. IC900 serves two other functions; it senses the presence of the
10.3KV through R921 and R932 and compares it against the 9.1 supply voltage to ensure a
regulated output, and also senses the varying current in either deflection coil. If no change is
detected, the IC shuts down the high-voltage oscillator to prevent the beam from "burning" the face
of the CRT.
The HV transformer (T901) is otherwise unavailable for replacement. These HV transformers are
extremely reliable compared to all other vector monitors out there, but if yours does go bad, you
will have to find another G08 HV cage for a replacement.
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G08 Vector Monitor Guide
CRT Neck Board
The CRT neck board is a 4” x 4” PCB with a large tube socket mounted directly in the middle of it.
It connects to the end of the monitor tube. The board controls the color guns of the tube.
The neck board has a few controls on it. One side contains a single “blue gain” control, while the
opposite side has “red cutoff”, “red gain”, “green gain”, “green cutoff”.
The color drive circuits accept a 4-volt maximum signal on the RGB inputs. The outputs drive the
three electron-beams in the CRT. Three neon glow-bulbs, NE-100, 101, and 102 act as spark
arrestors for the color-drive outputs to the CRT.
Most of the neck PCBs will have different Issues numbers screen into the top of the board and the
bottom of the board. It is unknown if there are any different revisions of the neck board. However,
this may be the one portion of the G08 monitor that was correctly designed, and you should have
little or no problems with the neck PCB.
Tube
This is large glass funnel shaped... it’s a monitor tube for crying out loud! The tube is nothing
special . It is a 19VLUP22, which is also found in the Wells Gardner 6100 color XY monitors.
However, these monitors often came with a “tinted gel” covering or shield over the front of the
monitor to make the vectors look better.
A degaussing circuit is provided through D404, D405, and R400. The CRT is automatically
degaussed when R400 is cooled sufficiently to conduct current through the degaussing coil.
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G08 Vector Monitor Guide
Part Number Summary
This following list summarizes all the Electrohome part numbers for the G08 monitors. These
numbers do not reflect the issue numbers between the deflection board revisions.