06/21/07, by email@example.com
Ok I admit I'm not the best video game tech. But as a pinball hack, I find myself in a position where I need to occassionally fix video games. The single biggest thing that needs repairs in the "classic" coin operated video games (1980-1984) are monitors. Games like Pacman, Ms. Packman, Galaxians, Gorf, Galaga, etc. all used the Electrohome G07 monitor. Think of the ElectroHome G07 as a 30 year old TV set (though it's really not, but that would be a good analogy). And this one monitor was most popular during the "classic" video years of 1980 to 1984. Of all the video games I see, this and the Wells Gardner 4600 are the two that were used the most.
So anyway, I decided to put together a document on how to systematically repair the ElectroHome G07. Note this won't fix every problem, but it will fix most. The reason I use this approach is simple - I really didn't want to spend a boatload of time learning how to fix monitors, so a systematic approach was one that I could apply to the ElectroHome G07 and get it working 90% of the time.
Typical G07 Problems.
An imploded G07 monitor chassis and neck board removed and on the workbench.
Close up of the cracked HV flyback transformer and the bad
Horizontal output transistor.
G07 Monitor chassis Removal.
Remember those old worn out electrolytic caps I talked about? Well believe me, they ain't worn out as much as you might think. That is, they can still hold a charge. Caps are a somewhat mechanical device that store and discharge electrical current, many times per second. In the case of a monitor, this voltage is very high, like 20,000+ volts. Also, as goofy as it may sound, the picture tube itself acts like a large capacitor! That means it stores current too. All this comes together at the monitor Anode, which is connected at the monitor tube through the electrode beneath the suction cup on the side of the monitor tube. This anode needs to be grounded to discharge the caps and the picture tube. This needs to be grounded BEFORE DOING ANYTHING to the monitor (including trying to remove the monitor chassis).
Discharge the chassis & Monitor Tube.
Blown or Missing Monitor Fuse.
If you have recently powered on the G07 chassis and the F901 fuse (closest to C904) was blown, then C904 has a nice fresh charge in it just waiting for you to provide a path to ground. Some caps hold their charge for years, while others dissipate in a matter of hours or weeks. So always discharge the G07 monitor chassis with F901 installed or with it jumpered with an aligator clip.
Stuff you'll need to buy for a typical Electrohome G07 monitor rebuild (flyback, 2SD870
HV Flyback Transformer.
Many people will, as a precaution, just replace the Flyback with a new one. They are not expensive, about $20. Frankly if you're going through all this work to rebuild a G07, you might as well install a new flyback. Because if the flyback implodes, it WILL take out several electronic parts with it. If usually takes out the F902 fuse, the Horizontal output and/or Regulator transistors, and perhaps an electrolytic cap or two in the process. Because of this, just replace the flyback and be done with it. Otherwise you'll be going through this whole G07 rebuild procedure again when the 30 year old flyback dies.
The dead flyback and horizontal output transistor.
Replacing the flyback is pretty easy. There are about eight solder points on the bottom of the monitor chassis that must be desoldered. And TWO screws on the side of the chassis that must be removed (which stablize the flyback). Don't forget to remove those two screws!
After the old flyback is out, don't put the new one in just yet. I do this dead last. Because it's a lot easier to do the all the other G07 chassis work with the flyback removed.
Testing the Output Transistors.
The horizontal output transistor X01, mounted by the
flyback. This is a 2SD870 transistor.
With a DMM set to the diode function, put the DMM leads on the two legs of the Horizontal output transistor (black DMM lead closest to the flyback). For the Regulator transistor C1106 on the other side of the chassis (furthest away from the flyback), put the black DMM lead on the transistor lead closest to the back of the monitor chassis. You should see a value between .150 and .600. A dead short will show as .010 or less.
Testing the horizontal output transistor mounted by the
flyback. This 2SD870
Testing the Regulator C1106 transistor mounted on the
other side of the G07 chassis.
When replacing an output transistor, first unsolder the wires from the transistor's legs. Then remove the two screws that hold the transistor to the metal chassis. Make sure you don't rip the insulating gasket under the transistor. Yes it's needed, so just be careful and you can usually reuse the old one. These insulators can be polyimide (thin yellow plastic), mica (translucent white), or elastomer (gray flexible rubber). Sometimes a very thin layer of silicon insulator grease (heat sink compound, Radio Shack) is used, but personally I don't add any. The grease fills the tiny holes in the metal to help with heat transfer (that's why you use a very thin layer).
The new transistor will only mount one way (unless you force it!) Do a continuity check between the outside of the transistor's metal case and the metal frame it mounts to - there should be no continuity. If there is continuity, you must replace the rubber or mica transistor insulator. If you fail to do this, you will kill the new transistor (and of course the monitor will not work).
When resoldering the wires to the new transistor make sure you don't mix up the wires. Also solder the wires to the ends of the transistor legs so they don't short against the metal frame or metal retainer. And don't forget the round insulating ceramic discs that mounted on the inside between the monitor frame and the metal wire holder. These insulators keep the mounting screws from shorting the metal case of the transistor to the metal chassis frame. The screws actually need to connect the transistor case (the collector) to the isolated metal retainer (and NOT the metal monitor frame), where it is then fed to the primary winding of the flyback transformer.
Note do not touch either output transistor while the monitor is powered on as there is high voltage there!
Resolder the Male Connector Pins and Large Resistors.
The two headers W102 and W103 are very important to resolder They are the negative sync (3 pins, top arrow in pic below) and the video & positive sync (6 pins, lower arrow in pic). If these pins are loose or the solder joints for the pins cracked, this is will cause a video sync problem, or missing color(s), or lack of vertical or horizontal sync, or any combination of these. If only one of the two grounds is connected, you will have nothing on the screen but a negative picture that cannot sync.
Some of the male header pins on the solder side
The video and sync male header pins and large resistors that need to be resoldered.
Also any large resistors (1 watt or larger) can get cracked and/or cold solder joints, and need to be resoldered. These are scattered along the monitor and neck board. A quick visual examination should locate any of these. And lastly check the neck board for cold or cracked solder joints.
The absolute best way to resolder these connections is to first remove the old solder. I use a cheap solder depullit device (Radio Shack) and desolder the contact points. Then I resolder them with new fresh solder.
Check the Fuses.
The F902 fuse at the back edge of the chassis board.
This fuse is most likely to be blown,
The F902 fuse at the back edge of the chassis board,
after replacement with a fuse holder.
Horizontal Width Coil.
Warning: If you have the monitor chassis upside down to solder the bottom of the board, often the Horizontal Width coil acts like a "leg". This is obviously not a good thing, as the coil could be easily broken. Be careful, as even a burnt looking Hwidth coil is usually fine, and replacements are hard to come by.
Installing the Cap Kit.
A capacitor's longer leg is the positive lead. Negative on the cap is also indicated by a band on the body of the cap, usually with a "–" sign. On the G07 chassis board, negative is indicated on the parts side of the board as a solid dot on the circle indicating where the cap installs. There is often a dot on the solder side of the board too, again indicating the negative lead of the cap.
Note the C302 cap has the polarity INCORRECTLY screened on the SOLDER side of the board. Interestingly the C302 polarity on the parts side of the board is correctly marked (just to confuse you).
The G07 cap kit should include the following capacitors:
Occasionally cap kits may substitute a higher voltage cap than indicated above. Higher voltage rated caps are fine, but using a lower rated cap is a bad idea (though some kits will do this, because they know a lot more about this monitor than me).
Note that EVERY ELECTROLYTIC CAP EXCEPT THREE get replaced on the G07 monitor chassis board. The only caps that don't get replace are C301, C520 and C904 (the big cap).
When I get a cap kit, I organize the caps into the installation
sheet to help aid me
After you have installed all the caps, VISUALLY CHECK from the parts side of the board that you did not install any backwards! I can't stress this enough - installing a cap backwards will cause an explosion (yes the cap explodes), and this will kill all of your enthusiasm in doing this project.
B.Roberts has a nice tip for checking cap orientation. If you look at a G07 Cap Map you'll notice that a majority of the negative cap lead "bullets" on the monitor board are facing the front of the chassis or toward the flyback. There are only four that deviate from this pattern, and three of those are under the metal protection shield (missing in all these pictures) and out of sight.
The caps with black "X" marks on them are what get replaced.
A chart of G07 cap positions from Lizard Lick Amusments.
A chart of G07 cap positions from B.Roberts. Note the perspective is
There is an optional C303 upgrade. Personally I never do this upgrade (and frankly find no need for it), but some claim it helps with screen "curling" problems. Here are the steps for that modification.
Check or Replace Resistor R908.
Install the Flyback.
Check the Neckboard RGB Transistors.
Double Check all Capacitor Installations!
A MIS-INSTALLED cap on a G07 chassis.
Clean Up Your Solder Work.
Lifted Solder Pads.
Isolation Transformer: REQUIRED.
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