*********************************************
The Evil, Infamous, Unreliable, Flaming...
Electrohome
_______ ________ ________
/ \ / \ / \
| ___ | | ____ | | ____ |
| | |__| | | | | | |____| |
| | ___ | | | | \ /
| | |_ | | | | / ____ \
| |___| | | |____| | | |____| |
| | | | | |
\_______/ \________/ \________/
FAQ version 0.6
**********************************************
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.
***********************************************
1. Introduction & Monitor History
2. Parts descriptions
a. Input protection board
b. Deflection board
c. Deflection transistor package (Heat sink)
d. HV Unit
e. Neck board
f. Tube
3. How it all works
4. Repair preparation
5. Debugging the monitor
6. Making the monitor more reliable
a. Input protection board mod
b. Deflection board mod
c. Heat sink mod
d. HV Unit mod
e. Neck board mod
f. Zanen's Cap Kit
7. Tube replacement
8. References
9. Contributors
10. Document History
*********************************
1. Introduction & Monitor History
*********************************
Ok, enough making fun of the G08 :-). It's
actually a pretty strong monitor considering the
work that it does, and when it's working it is
a fairly impressive color vector monitor. However,
the horror stories about this monitor are true (and
the list is long), so and having a fire extinguisher
handy around this monitor certainly wouldn't hurt.
The Electrohome G08 is the monitor model that was
used in the Sega/Gremlin color vector games and in
Cosmic Chasm. The first version of the Electrohome
monitor was G08-001. This monitor, however, was very
prone to failure due to flaws in its design.
Sega/Gremlin attempted to remedy the situation by
implementing what they refered to as the monitor
replacement program. The G08-003 monitor was later
released, which appears to simply be a hacked G08-001
monitor with some significant changes. These
modificiations (supposedly) made the monitor more reliable.
The G08-001 used MJ15003 deflection transistors
and had direct connections from the deflection
transistors to the deflection board.
The replacement version of the monitor was the
G08-003. This monitor used 2N6259 deflection
transistors and featured two additional "paddle"
boards that plugged in between the deflection
transistor connectors and the deflection board.
These boards were an attempt to add short circuit
protection for the output transistors. I have never
seen these work correctly, however, as often the
parts on the paddle boards are toasted. Later
revisions of the monitor didn't have these boards,
as their circuitry was integrated into the main
deflection board.
Also, the G08-003 deflection board had large ceramic
wire-wound resistor "tee-pees", which were
two resistors soldered in series and glued
into place. These replaced the original 20Watt 3ohm
resistors.
I have a copy of the Electrohome G08 monitor for
version G08-001, and it has the schematics in it
for G08-003 labeled as "future reference". It
shows the G08-003 using MJ15003 transistors (and
MJ15004 transistors also...) However, I believe
this schematic actually differs from the G08-003
schematics found in the Star Trek manual. Every
G08-003 monitor I've seen has always had the
2N6259 transistors
The Sega Gremlin cocktail games used the same
monitor, just mounted on a different chassis which
would fit in a cocktail. The same HV, deflection
transistors heat sink, and deflection boards are
used in the monitor, however, so parts from an
upright and cocktail are interchangeable. The
Space Fury cocktail I picked up had a G08-003 monitor,
but I've seen at least one Sega Gremlin cocktail game
used version G08-004, apparently another revision.
I don't have any details about the G08-004.
Cosmic Chasm uses still another version which is
labeled G08-CC0 (or G08-005, depending where you
look on the monitor label). There is speculation
that possibly they made this version of
the monitor simply for this one game. It was
made around Oct 1982, and it uses SDT 1064's for
deflection transistors. A special transformer used
for this game outputs 49VAC from the center tap.
Apparently there are no "kludge" boards between
the deflection transistors and the main board
on this version.
We'll talk about each piece of the Electrohome G08
monitor individually, and then we'll talk about 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 G08 monitor.
The following information is a compilation of
conversations, e-mails, and chats betweem 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 & timing
boards that are in the G-80 boardsets.
"At the time I came to work at Sega, the G80 setup was
already there. I think AstroBlaster 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 rep. who
was lecturing at Cal.. 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 G80 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 whoever they wanted,
and always won. The G05 design (Asteroids, Asteriods 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 definately 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..."
********************
2. Part Descriptions
********************
======================
Input protection board
======================
This small 1 1/2" 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 do some "trimming
down" of the inputs.
This small board is the first interface into the monitor.
Since it is screwed to a thin piece of metal, usually
you'll find tape on the back of this board to
prevent the header pins from grounding to the metal.
================
Deflection board
================
This large PCB is mounted to the bottom of the
chassis (7" x 10"). The G08-003 version will also have
2 vertically mounted PCBs (2" x 2") or "paddle boards"
connected to it which mount on the header pins on the
right side of the board. The deflection board creates
a low voltage power supply for the HV board and controls
the X and Y video amplifiers.
The right side of the board is mostly deflection circuitry,
while the left side of the board is mostly a low voltage
power supply.
=========
Heat Sink
=========
This metal box is a heat sink which 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 are MJ15003 for the G08-001.
These transistors were replaced with the more heavy-duty
2N6529 transistors in the G08-003 model. Unfortunately,
the 2N6529 transistors have been discontinued, making it
difficult to find these now rare beasts.
The deflection transistors tended to fail due to
failing power supplies and vector boards that freaked
out. To make matters worse, the fuses for the deflection
transistors would often fail AFTER a few components
were taken out.
=======
HV unit
=======
The HV (high voltage) unit consists of a PCB mounted in
a metal box. Affixed to the board are a HV transformer
and a single control. A small PCB (1" x 2") will be
mounted to the outside of the box. The HV unit creates
the high voltage for the tube (~19.5 kV) as well as the AC
voltage for the heater.
The PCB is mounted in a metal frame, and a 10-pin
header is attached to the top of the box. The pinouts for
the 10-pin header are as follows:
1 - Y
2 - X
3 - -9.1VDC
4 - +9.1VDC
5 - GND
6 - GND (heater)
7 - +6.3VAC (heater)
8 - +126VDC
9 - NC
10 - VG2 (variable gain; part of brightness circuitry)
The PCB has three controls on it: R917 (frequency
control), R918 (duty cycle), and R933 (sensing voltage).
Twiddling these pots in various ways makes can help make
the monitor more resistant to HV shutoff. 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.
The purpose of the duty cycle control remains a mystery.
The large control on the HV unit is the focus.
The small PCB affixed to the outside of the metal cage
is a voltage regulator which regulates the input +126VDC
to +100VDC.
==========
Neck board
==========
The 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. When mounted
to the tube and looking at it from the back, the controls
go clockwise from the upper right: red gain, red intensity,
green gain, green intensity, blue gain.
====
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.
===================
3. How it all works
===================
Inputs come in from the game boards (most commonly the
Sega G-80 system XY timing and control boards) and are
fed into the input protection board. The inputs then
go to the deflection board, and the deflection board does
its stuff. The deflection board sends an "OK, these
signals are cool" signal to the HV unit, which turns on
and provides the HV to the monitor and the AC to the
heater. The deflection board then feeds the color
signals to the neck board, and controls their position
with the deflection coil.
The monitor has a unique spot killer system, in that if
it receives no valid inputs from the game board, the
monitor will shut down the high voltage. This method of
self-preservation differs from that built into the Wells
Gardner 6100 color XY monitor, which, in a zero-deflection
mode, shuts down the Z amplifier, which is like turning
the brightness level to zero. The G08 has no Z amp, and
must protect itself by more drastic measures.
======================
4. Repair preparation
======================
So you have a G08, and you have no idea of its condition.
Well, let's do a few basic things before we fire it up
("fire it up" might be a poor choice of words here ;-)).
1) Start by dismantling the monitor.
First, discharge the monitor tube. There is high voltage
under the monitor's anode cup if the monitor has been powered
up recently. It may not be necessary to disharge a monitor
tube that has been sitting for a while, but it's best to
be on the safe side, so get in the practice of always
discharging a monitor tube before you begin work on a monitor.
To discharge the tube, place the monitor on a non-conductive
surface. Do not touch the monitor with your hands while
doing this procedure, as we will be discharging the monitor
to the monitor chassis. Locate the anode cup; it is the
suction cup thingy attached to the tube which has a red
wire coming out of it. A few inches from it, there is
a metal shield which surrounds the back of the tube. We
will be discharging the tube to this shield. Insert a
long screwdriver with a plastic handle under the anode cup,
and tilt the screwdriver such that it also makes contact
with the metal shield. There should be a few quick snaps.
Hold the screwdriver there for a second, and then you are
done.
Next, remove the neck board, as bumping it may cause you
to break the tube's neck. Getting it out of the way will
keep you from accidentally bumping it when trying to reach
other parts. Next, unsolder the wire that goes from the back of
the focus knob to the neck board. This is required in order
to separate the HV unit from the deflection board.
Everything else is connectorized and screwed together,
so it should be easy enough to take the monitor apart.
I start by removing the neck board first because a while
back when I was working with these monitors, I would swap
out HV cages for testing purposes. I found that when
I would pull off the 10 pin connector on the HV unit,
the momentum of the pull would cause me to bump the
neck board. I finally ended up busting the tube's
neck. Now I always remove the neck board before
disconnecting anything else.
2) Check the deflection transistors.
Visually inspect the transistors and make sure they are
even correct in the first place. I've seen operators
attempt to substitute other types of transistors in for
the 2N6259s or MJ15003s, so make sure they are correct to
start out with.
Test the transistors through the connectors. Unlike the
Wells Gardner 6100 color XY monitor, which uses 2N3716 and
2N3972 transistors in a push-pull configuration, all the
transistors in the G08 should be identical.
Deflection transistor harness connector
1 - emitter #1
2 - collector #1
3 - base #1
4 - NC
5 - emitter #2
6 - key
7 - collector #2
8 - base #2
You should get a definite reading between ??? and ???.
You may get a slight reading between ??? and ??? if there
is a ?? ohm resistor across the emitter and base, which is
found in the G08-003, and is missing in the G08-001. Most
shorts will occur between the collector and either the base
or emitter. If your test through the connector reveals a
short, pull the transistor and test it separately. If it
is good separately, you may have accidentally shorted either
the base or emitter against the heat sink, or the transistor
socket may have been bent. If the transistor tests bad
detached from the heat sink, it's ready for the garbage.
If you have to replace transistors, replace them all with
the same type. MJ15003's are a good replacement (and were
used originally) which are probably easier to find than the
2N6259's. But if you can get the 2N6259's, I would use
those.
3) Resolder the vertical header pins.
These are the pins which the connectors connect to. Don't
just reflow the solder; add a little more to each pin (don't
overflow onto adjacent pins, though). Double check your
work with an ohmmeter when you're done.
4) Do a visual inspection of the boards.
If you look at the bottom of the HV PCB or the bottom (or
even top) of the deflection board, you may see cut traces
with jumper wires here and there, some resistors, transistors
and diodes soldered to the bottom. Don't let this frighten
you. Assume that these are "factory modifications" and
leave them alone.
Look for burnt resistors, loose capacitors, broken solder
joints, and broken transistor legs. Resolder anything that
looks suspect. If the deflection board has the paddle boards,
carefully inspect these as these commonly have destroyed
components. Increase the amount of solder on the joints
for the large capacitors and the HV transformer; I have
seen broken solder joints cause failures in both cases.
Make sure the heat sinks on the small transistors on the
deflection board are NOT TOUCHING ANYTHING except the
transistor it is trying to cool. Replace burnt resistors
and loose capacitors. If you can, it's a good idea to
replace all the electrolytic capacitors on the deflection
board anyway (except for the LARGE ones), since these
components tend to dry out and fail as they age. If you
have to replace current sense resistors, use non-inductive ones.
5) Do an ohmmeter inspection of the board.
Test the diodes on the board. Put the negative lead
on one end of the diode, and the positive lead on the other
end of the diode. Then reverse. You should get a "definite"
reading only in one direction (due to testing in circuit, you
may see a negligable reading in the other direction).
Test the transistors on the board. This is a little hard
to do in-circuit, but you should get a definite reading in
at least two of the combinations, and none of the
combinations should look like a short.
Test the fuses. A visual inspection may not catch a blown
fuse. Use the ohmmeter across the fuse holder, not just
the fuse itself.
6) Reassemble.
Reconnect and screw things into place. Resolder the focus
knob lead. Double check your work.
Well, this is about all you can do to prepare for launch.
Let the count down begin....
Connect the monitor to a known good boardset. Here's the
catch-22: if you picked up a non-working game, you won't
know if the monitor is bad, or the boardset is bad, or both.
You've got two unknowns, which could make monitor debugging
a real pain. My advice, therefore, is to NOT test with an
unknown boardset.
Do what you can to borrow someone's working set to test
the monitor. The unknown monitor has virtually NO chance
of hurting a working set of boards (unless the monitor
decides to torch the whole cabinet. ;-)). The following
debugging section assumes you have a working boardset.
========================
5. Debugging the monitor
========================
Ok, to debug the monitor, you'll need a known-working
boardset and power supply. Hook up the power and video
inputs.
****************************************
WARNING: Working with monitors of unknown
operating condition can be EXTREMELY dangerous.
The Electrohome G08 is no exception. If fact,
there are probably more horror stories about this
monitor than any other. Proceed with extreme
caution.
****************************************
Flip the power switch (but be prepared to flip it
off again quickly).
Symptom: No picture. No fuses blow. All is quiet.
Make sure everything is hooked up, and that the boardset
is running correctly. If so, you've got problems in
the deflection circuitry.
Symptom: No picture, but you can hear deflection chatter.
If the heater is glowing, that means you have HV, and
you should be able to get a picture. Adjust the screen
brightness to see if any lines are being drawn. Adjust
the intensity and gain knobs on the neckboard accordingly.
If at this point you have a dot in the middle, or a line
across the screen, you have a problem in your deflection
circuitry.
If the heater is not glowing, most likely you have no
HV. Double check by using a HV probe. If there is HV,
something is wrong with the heater connection or the
tube itself.
If there is no HV, check the voltages on the 10 pin
connector on the HV unit. Be careful not to short
the pins together! The voltages are listed above.
If the voltages look good, and there is still no HV,
there is something wrong with your HV unit. At this
point, it probably wouldn't hurt to fiddle with the
pots on the HV unit.
Another symptom I have seen related to this one is
that the picture comes up fine, but after a few
minutes, the picture disappears. I would suggest
wiggling or pressing in on the 10-pin connector
going to the HV unit. Intermittent connections
can cause the HV to drop out. I have seen cases
where flexing the HV unit PCB can cause the HV to
go on and off. Resolder, resolder, resolder until
the intermittent connection is found.
Symptom: Fuse 700 blows.
Check transistor ???
Symptom: Picture has retrace lines between points, and a
bright dot is in the center of the picture.
If the dot is one particular color, twiddle the pots on
the neck board. These control the drive of the color guns.
If there is still a dot, try turning down the brightness
control on the deflection board. Sometimes the solder
joints for this pot, and the nearby resistor, break and
can cause the brightness to shoot up too high.
Symptom: The neon bulbs on the neck board are glowing.
These are not supposed to light. These are spark
gap bulbs, meaning that if they light, your guns
are sparking internally. Most likely there is a
problem with the tube.
When debugging the monitor, you may need to swap the
deflection board in and out a lot, and it get's to
be a pain to hook up the focus each time. If you
want, you can actually leave this lead disconnected
while debugging, but when you finally get a picture,
remember that the picture will be extremely out of
focus. However, you will be able to tell that there
is a picture there. Also, double check that all the
connectors are connected each time you swap out the
deflection board.
===================================
6. Making the monitor more reliable
===================================
Ok, so now you have a working G08 monitor (hopefully).
Here are just a few things you can do to the monitor
to prolong its life just a bit longer.
--------------------------
Input protection board mod
--------------------------
Replace the tape on the back of the input protection
board with a strip of electrical tape to prevent it
from shorting to the metal strip it's mounted on
when you are plugging in the input connector.
--------------------
Deflection board mod
--------------------
Replace the 16VDC rated capacitors with 35VDC rated caps.
I have seen several different versions of the
"factory modifications" that were made to these monitors.
I have no figures on which modifications make the monitor
more reliable.
-------------
Heat Sink Mod
-------------
The deflection transistors mounted on the heat sink can
be more efficiently cooled if you place them on the
inside of the heatsink instead of on the outside. To
do this:
1) Remove the heat sink assembly from the monitor chassis
by removing the screws in the side of the chassis and
disconnecting the fan and deflection transistor harnesses
from the deflection board.
2) Remove two upper or lower screws from the fan so that
the heat sink assembly can be split in two.
3) Unscrew the transistors from the heat sinks.
4) Place the transistor sockets on the outside of the
heatsink, and mount the transistors on the inside of
the heat sink. Make sure to reinstall the mica insulators
with plenty of silicon grease on both sides.
5) Reassemble and remount. Before hooking up the transistors
again, do a transistor test through the connectors (as
mentioned previously in this document) to make sure that they
are mounted correctly.
6) Reconnect the fan and deflection transistor harnesses
to the deflection board and retest the monitor.
The deflection transistors should run much cooler now.
One of the main problems with the fan-cooling setup is
that the airflow through the closed cabinet is pretty
miserable. You may want to consider running your Sega XY
cabinet with the back removed.
-----------
HV unit mod
-----------
None available at time of printing.
--------------
Neck board mod
--------------
None available at time of printing.
---------------
Zanen's Cap Kit
---------------
Zanen Electronics (806) 793-6337 has a monitor rebuild kit for
this monitor. The kit is number 110. There are a few problems
with the kit, however:
1) The transistors shipped with the kit are 2N3716. These
transistors are not sufficient to work with this monitor.
Instead, replace them with MJ15003 transistors as mentioned
above.
2) Their kit says to replace C401 with a 1000uf 50VDC rated
capacitor. It should be a 1000uf 160VDC rated capacitor.
===================
7. Tube replacement
===================
If you are unfortunate enough to come across a G08 with
a bad tube, there is still something you can do about it.
You can replace the tube. As mentioned before, the
tube is the same as the one used in the Wells Gardner
6100 series color XY monitors, but it can be substituted
for some of the more common monitor tubes with similar
results.
To do this, first get a spare tube. You can buy a
brand new color vector tube (19VLUP22) from Richardson
Electronics (1-800-222-2787) for around $165.
The following tubes can also be used with relatively
good results:
- Disco monitor tubes
- Wells Gardner 4600 series tubes (19VLTP22)
Hopefully the tube you get will have the magnetic rings
still in place.
On the spare tube, mark the location and position of the
magnetic rings. Remove them, and place the G08 yoke
on the tube. Put the magnetic rings back on in their
original positions. Try it out. Adjust the yoke
as needed. The tube is deeper, so you may not
be able to have things exactly as they were before.
For example, the caps on the deflection board may now
touch the monitor, and you may not be able to screw the
deflection board back to its original place. Also, the
neck board will be farther away from the HV unit now, so
so may need to lengthen the wire from the HV unit to the
neckboard. If you do, make sure you use special high
voltage wire.
NOTE: I tried doing a tube swap with a 19VJTP22 tube
from a WG monitor (4900 or 4600, can't remember).
I did not have any luck. While the picture was fine,
I could not adjust out the green band down the middle
of the picture. Apparently this is due to the fact
that the deflection coil could not be positioned
far enough down the neck tube (because the degree
of the neck tubes are different).
=============
8. References
=============
1. The 'Wiretap' Arcade Game Collector's Archive
http://www.spies.com/arcade/
Contains information about G-08 system games, as well
as schematics for the monitor and game boards.
2. Star Trek Manual
This manual contains the most up-to-date information on
the Electrohome G08-003 model monitor.
3. Sega-to-Atari color XY circuit
If you've given up on the G08, this is an alternative
solution.
===============
9. Contributors
===============
Mark Jenison (
[email protected])
David Shuman (
[email protected])
Michael Kelley (
[email protected])
Al Kossow (
[email protected])
====================
10. Document History
====================
Version 0.1: Looking for contributors
Version 0.2: David Shuman's additions
Version 0.3: Michael Kelley's 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
