A resource for repairing & restoring your Galaga
Tips:
A classic case of bad video ram on the video pcb. Bad video ram usually causes vertical lines in some or all of the graphics. Take a look at the pictures below, and this screen shot.
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If you have some of the following problems, a little "house cleaning" can get you going!
I took the boards out of my galaga last night. I reseated most of the socketed chips and cleaned the contacts on the chips and I reseated the edge connector. I put the boards back into the machine, and voila! all my problems disappeared. The machine is playing perfectly!
Just for reference purposes, the problems I had that got fixed:
Scott B.
Installing a switching power supply
One item that will need replacing is the power supply. Finding parts to repair the old PS can be quite hard, so you will be better off installing a new switching PS.
If you do install a PS, you will eliminate the need of two parts from the game:
1-The PS transformer (the big one)
2-The PS PCB (the PCB with the big ass heatsink mounted on the side)
Follow these 8 steps:
Many people find it easier to combine all the yellow wires into one wire before tying them to the switching supply due to fact that there are so many (around 10). Same goes for the +5 (3 or 4 red wires and the one white one). There is only one orange +12 wire.
Note: The white wire is for the coin meter, and -5 is NOT used.
Galaga presents several problems from a troubleshooting perspective. First and foremost, in my opinion, is that the board is of a very poor design. The components used in fabrication are of poor quality and experience a very high failure rate. The sockets used across the board are especially troublesome. I have had occasions where I have opened the back door of the game only to find that an EPROM or custom I.C. has worked its way out of the socket and is laying in the bottom of the game. This just from the normal vibrations given the cabinet during gameplay! The designers seem to have emphasized hiding the function of
chips over providing for serviceability. As a result of this effort, Galaga is overpopulated with unnamed custom chips, they are all the black chips identified only by four number. Here is a breakdown of the custom chips:
* 00xx Address multiplexer for fixed RAM between CPU and video clocks
* 02xx Custom shift register for data from graphics ROMs
* 04xx Motion object and scratch RAM to CPU bus interface
* 05xx Generates blinking star backgrounds (specific to Galaga)
* 06xx Bus interface
* 07xx Clock divider counter array
* 08xx Multiprocessor data bus interface
* 51xx Input I.C., Player/DIP-switch/etc.
* 54xx Generates "explosion" sounds (I believe this is just a Z80 with some pins swapped to hide its purpose)
Working with a Dead Board
When I first work on a non-functioning Galaga, I always first pull every socketed chip and clean the legs of the chip. I usually use a small brass brush the size of a toothbrush to clean the legs, but be very careful as the legs are often brittle and will break off at the smallest application of force to them. Some recommend using a pencil eraser for this, but I have never tried it. I also use gold-plating contact cleaner to spray the legs of the chips after I have cleaned them. Gold Guard and ProGold are common brands. Occasionally I will use a little contact cleaner and spray it into the socket itself. This tends to help the connection between the socket and the chip.
Another common point for failure is the ribbon cable between the two boards. Often this cable is loose or becomes loose while the board is being installed. I usually pull the cable off and clean the contacts with contact cleaner. If the cable is extremely loose, I will sometimes use a couple of dots of hot glue to secure the cable in place.
If your Galaga is booting up and then freezes on the "RAM OK" screen, check your power supply! Almost always there is a problem with the +5. Check the voltage at the chips and adjust the power supply until the voltage is 5.1 or so. A problem with the +5 can also cause the game to reset randomly during game play, although it usually happens when the game first boots up. Always check the voltages (at the chips) first, before going on to more advanced troubleshooting. I have also seen a bad Z80 cause this.
The card edge connect at the top of the board and the filter board can also develop loose or bad connections over time. I usually clean the edge connectors on both the filter board and the CPU board when I first start to work on a board. Occasionally a component on the filter board will fail and you will loose a signal, this is usually manifest as a lost color or sync on the monitor or the loss of some input such as the control panel buttons and may also cause a loss of sound altogether.
Problems with Gameplay
One of the more common problems I have seen with Galaga boards is a problem with the sprites (moving objects on the screen., i.e. the players ship, enemy bugs, etc.). Usually this looks as if each sprite is a block of moving vertical white lines. Every single instance of this problem I have seen has been a failure of some sort of the 04xx chip. Usually the chip is just loose because of a poor socket or the legs have become oxidized and are making poor contact.. Cleaning the pins of the chip or replacing the socket clears this up. Occasionally the chip itself fails, in this case you will need to locate a working replacement (see my discussion later on finding replacement chips).
I once had a board that had vertical "tearing" of the sprites. It looked as if every other row in the sprites was being dropped toward the bottom of the screen. I finally traced this problem to the power supply. The tearing would appear when the board was used with an original Midway linear power supply, but disappeared when used with a modern switching power supply.
If your board is re-booting at the grid screen, but occasionally makes it farther, check the 06xx at location 6L. (Can't really just check it, try swapping with a known good one).
Sound Problems:
The main audio output is amplified by an MB3730, this chip is becoming increasingly hard to find and expensive when you do find it. I recently spoke to Consolidated Electronics who were about to import a shipment of MB3730s from Asia, the price quoted to me was around $35 a chip. But don't fret!, you can cannibalize MB3730s from the Midway MCR II series games. These games, such as Tron, Spy Hunter, Two Tigers, etc. use a small sound amp board called the "Dual Amp Board". Each board has two MB3720s on them and they can fairly easily be had. I often cannibalize the Dual Amp board for Galaga amps.
If you are missing all but the explosion sounds, there are two BiPolar ROMs on the top (CPU) board that are part of the circuit that generate all the other sounds; chances are that one or both of these are bad. Another problem area is the two 7489 RAM chips in the same circuits go bad. You can also look for resistor packs in the same area that have leads detaching from them.
Locating Custom Chips
If you do have a failed custom chip, one of the best places to get them are from Dig Dug boards. Since Dig Dug was also designed by Namco, it uses many of the same chips as Galaga. Only the 05xx and the 54xx chips are specific to Galaga, all others are also used by Dig Dug. I keep a stack of them around just for fixing Galaga boards.
Distorted sounds: Sound decoder prom at 1D , the 74273 at 3B and the CD4066 at 3A; failure of any or all of these can cause distortion or loss of sound.
James
jamesm@erinet.com
Some Galaga PCBs use the weird resistor pacs, that are some sort of flat ceramic package with leg/pins soldered/pressed on. These are very unreliable with time and if they are ever bent. In my particular situation the 2.2K ohm pack RM17 was iffy and as a result I would get the dreaded RAM XX bad. Swapping the RAMs was not the solution. I placed 8 individual 1/4 watt 2.2K Ohm resistors, tied together at the top & fed to pin one as my fix.
Last updated: 8-31-2000 by Steven Gregory sgregory@arcadeshop.com
