Electrohome G08 Manual

							G08 Vector Monitor FAQ & Guide Page 11 of 39   The pinouts for the HV 10-pin header are as follows: 
 
Pin # Description 1 Y 2 X 3 -9.1 VDC 4 +9.1 VDC 5 GND 6 GND (heater) 7 +6.3 VAC (heater) 8 +126 VDC 9 NC 10 VG2 (variable gain; 
part of brightness circuitry)  
 
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 the High 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) or “flyback” as it is commonly referred to 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. 
 
 
  
						

							G08 Vector Monitor FAQ & Guide Page 12 of 39   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 Issue numbers screened 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. 
  
						

							G08 Vector Monitor FAQ & Guide Page 13 of 39    
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. 
 
  
Monitor Electrohome 
Part Number G08-001 Manual   EHT Supply Assembly G08-001 02-170003-01 Deflection Amp PCB Assembly G08-001 02-170005-01 CRT Socket PCB Assembly G08-001 02-170006-01 Heat Sink Assembly G08-001 02-170004-01 G08-003 Preliminary Manual  EHT Supply Assembly G08-003 02-170002-02 EHT Regulator Assembly G08-003 02-170016-01 Input Clamp Assembly G08-003 03-170021-01 Deflection Amp Assembly G08-003 02-170005-02 Horizontal Current Limiter G08-003 03-170020-01 Vertical Current Limiter G08-003 03-170020-02 CRT Socket PCB Assembly G08-003 02-170006-01 Heat Sink Assembly G08-003 03-170025-01  
  
						

							G08 Vector Monitor FAQ & Guide Page 14 of 39    
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 input signals 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 picture tube 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 yoke. 
 
The G-08 monitor has a unique spot killer system, in that if the monitor 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 amplifier, and must protect itself by more drastic measures. 
  
						

							G08 Vector Monitor FAQ & Guide Page 15 of 39    
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 discharge a monitor tube that 
has been sitting for a while, but it is 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. 
 
There are many ways to discharge a tube. The recommended way is via a High Voltage probe.  
Connect the ground of the HV probe to the monitor chassis, and insert the probe end 
underneath the anode cup and watch the voltage go to 0 (do not touch the chassis during this 
procedure).  However, as some people may not have access to a HV probe, a cheaper (but less 
safe) alternative is provided below. 
 
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 that has a red wire coming out of it. 
A few inches from it, there is a metal shield that 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 
the neck board 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. 
 
Make sure you have removed the neck board from the tube before removing the 10-pin 
connector on the HV unit!  Trust me, you are less likely to break the tube’s neck this way. 
 
2) Check the deflection transistors. 
 
Visually inspect the transistors and make sure they are even the correct transistor type. I have 
seen operators attempt to substitute other types of transistors for the 2N6259s or MJ15003 / 
MJ15004, so make sure they are correct to start out with.  
  
						

							G08 Vector Monitor FAQ & Guide Page 16 of 39  Test the deflection transistors through the connectors. Please read the procedure in “Appendix 
B” before continuing.  
 
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 (unless you have 
an original G08-001 which used the MJ15003 for one set, and MJ15004 for the other set). 
 
Deflection Transistor Harness Connector 
 
Pin Description 1 emitter #1 2 collector #1 3 NC 4 base #1 5 emitter #2 6 collector #2 7 base #2  
Get out your multimeter and do a resistance test between the following pins, using the red and 
black probes (indicating + and common/ground, respectively). Example: 1Red means you are 
touching pin 1 with the red probe. These tests are performed with the power turned OFF. 
 
Typically, there is a 100-ohm resistor across the transistor #1. If so, you will get these readings: 
 
Deflection Transistor Resistance 
 
1Red - 2Black: 20 ohms 1Red - 4Black: 0 ohms 2Red - 1Black: 100 ohms 2Red - 4Black: 0 ohms 4Red - 1Black: 50 ohms 4Red - 2Black: 0 ohms 5Red - 6Black: 0 ohms 5Red - 7Black: 0 ohms 6Red - 5Black: 20 ohms 6Red - 7Black: 20 ohms 7Red - 5Black: 0 ohms 7Red - 6Black: 0 ohms  
 
If yours does not have the 100-ohm resistor, you will get both transistors reading like the 
bottom half of the table above.  
						

							G08 Vector Monitor FAQ & Guide Page 17 of 39   
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 out of circuit, 
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 is 
ready for the garbage. 
 
If you have to replace transistors, replace them all with the same type. I would use 2N6259s, 
but these may be very difficult to find. MJ15003’s are a good replacement (they were used 
originally), and are probably easier to find than the 2N6259’s. Again, if you have a G08-001, 
you must use the MJ15003 and MJ15004 combination. 
 
3) Resolder pins, joints, etc. 
 
There are a few key points that generally need resoldered on these monitors.   
 
Resolder all header pins. These are the pins that accept connectors. Check all the header pin 
joints on the bottom of the deflection board, the current limiting boards (if present), the input 
protection board, and the HV unit. Do not just reflow the solder; add a little fresh solder to each 
pin (do not overflow onto adjacent pins, though). Double-check your work with an ohmmeter 
when you are done. 
 
Another common place where solder joints go bad is the HV regulator PCB.  Sometimes the 
regulators on this board get bumped and they break. Unscrew the HV regulator PCB from the 
side of HV unit and resolder the pins to the HV regulators. 
 
Be very careful when resoldering devices, as the screen has traces that lift very easily. 
 
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. Do not 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 current limiting boards, 
carefully inspect them as they commonly have destroyed components. Reflow and increase the 
quantity of solder on the joints for the large capacitors and the HV transformer. I have seen 
broken solder joints cause monitor failures in both cases. Make sure the heat sinks on the small 
transistors on the deflection board do NOT TOUCH ANYTHING except the transistor it is 
trying to cool. Replace burnt resistors and loose capacitors. If you can, it is a good idea to 
replace all the electrolytic capacitors on the deflection board (except the LARGE ones), since 
these components tend to dry out and fail as they age. 
 
5) Do an ohmmeter inspection of the boards.  
						

							G08 Vector Monitor FAQ & Guide Page 18 of 39   
Test the diodes on the HV and deflection boards. Put the negative test lead on one end of the 
diode, and the positive test 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 negligible 
reading in the other direction). 
 
Test the transistors on the HV and deflection boards. 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. 
This is about all you can do to prepare for launch. Let the count down begin.... 
 
Connect the monitor to a known good game boardset. Here is the catch-22:  if you picked up a 
non-working game, you won’t know if the monitor is bad, or the game boardset is bad, or both. 
You have two unknowns, which could make monitor debugging a real pain. My advice, 
therefore, is to NOT test with an unknown game 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 game 
boardset. 
 
If you don’t have a working game boardset to test with, contact Mark Jenison 
([email protected]) and he should be able to help you out in most cases. 
  
						

							G08 Vector Monitor FAQ & Guide Page 19 of 39    
DEBUGGING THE MONITOR  
 
Ok, to debug the monitor, you will need a known working game boardset and power supply. Hook 
up the power and video inputs to the monitor.  
 
 
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.  
 Symptom:  No picture; No fuses blow; All is quiet 
 
Make sure everything is hooked up, and that the game boardset is operating correctly. If all that 
checks out, you have most likely have 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 on the screen. 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. Check for the presence of HV by 
inserting an HV probe under the anode cup. You should read about 19.5 KV.  If there is HV, 
something is wrong with the heater connection or the tube itself (possibly a bad tube). 
 
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 below: 
 
Pin Description Pin 1 
Pin 2 
Pin 3 
Pin 4 
Pin 5 
Pin 6 
Pin 7 
Pin 8 
Pin 9 
Pin 10 Approx +2.8VDC 
Approx +3.5VDC 
-9.1VDC            
+9.1VDC     
GND         
GND (heater) 
+6.3VAC (heater) 
+126VDC 
NC 
Approx 400 VDC   
						

							G08 Vector Monitor FAQ & Guide Page 20 of 39    
Wiggle, press or flex the 10-pin connector on the HV unit. Intermittent connections can cause the 
HV to drop out. If this restores HV, reflow and resolder the HV header pins until the intermittent 
connection is repaired.  You may want to try replacing the connector pins as well. 
 
If the voltages on the 10-pin connector 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 try adjusting pots R933 and 
R918 on the HV unit.   
 Symptom:  Fuse 700 blows 
 
Check transistors Q703; Q704; Q705; Q706.  These fuses almost NEVER blow, so something must 
be REALLY screwed up. 
 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, adjust the color 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.  If the dot is still present, try adjusting R933 on the HV unit. 
 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 quite often, 
and it gets to be a pain to hook up the focus each time. If you want, you can actually leave this lead 
disconnected while debugging. Tie a piece of electrically tape around the end so it does not 
accidentally touch anything. When you finally get a picture, remember that the picture will be 
extremely out of focus. You will, however, be able to tell that there is a picture. Also, double check 
that all the connectors are connected each time you swap out the deflection board. 
 Symptom: Picture, But Only Partial Deflection, or Just A Vertical or Horizontal Line 
 
Part of your deflection is failing. Check the appropriate section of the deflection board, which deals 
with that range of deflection. The components in the 700’s are for the “X” deflection, and the 600’s 
are the “Y” directions. 
 
 Symptom: Occasional Extraneous Vectors On Right Side Of Screen