Galaxian Artifacts

Atarilogic

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I recently bought a Galaxian arcade unit, but the monitor is flashing weird artifacts every 2 seconds. Here is a shot:

see attachment -or- http://tonedefsystems.com/arcade/galaxian-damage.jpg

The monitor appears to be working, but there is a problem nonetheless. Has anyone seen this before who can give me an idea where I would need to start diagnosing? Also, any links to resources and general costs would be appreciated. Known/tested PCB swaps?

I look forward to becoming a member of this community and sharing my latest finds.

Thanks!
 

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Here is what I found at http://www.arcades.plus.com/galaxianfix.htm:

CPU Checks

If you still get a screen of rubbish, then there are some extra things you will need to check.

The first of these is the reset circuit. Reset (pin 26 on the z80) should start low when you switch the board on, and then rapidly go high. If it is pulsing, then the watchdog is probably kicking in.

If the game starts going through the self-test (various patterns on screen) but keeps re-starting the test, then the other line to check is the interrupt. (pin 16 on the z80). Now this is trickier to test, since it will only start pulsing when it is enabled by the software!

Normal cause of problems here are the enable latch (pin 5 of 9N) or the fact that the memory mapping for this has changed (some games move the interrupt enable, so check for linked pins or cut tracks)

---

Does this make sense to any repair people out there?
 
I am unclear on your problem. Is the game playing OK but the graphics are glitching every 2 seconds?

Or, is the game not running but every 2 seconds the graphics scramble differently?

Or some other option?
 
On power up, the screen alternates between odd code and blank screen. The monitor is displaying, but the game never boots. My previous post seems to make sense if the machine is running some diagnostic (odd code) and then resetting (blank screen). It just goes on and on like that never getting to the actual title screen. Does that make sense?
 
Sounds like it's going through the self tests but never finishing.

This can be dirty ROM legs, poor socket connections, bad ROMs, bad RAMs, etc... Watch the screen carefully when it goes blank to see if it flashes something up on the screen in the upper left corner such as RAM 1

RJ
 
Okay. Problem partially solved. I realize after inspecting the board that someone has knocked off the chips at 4K and 4J (video ram?) and 8F and 8H (buffer?).

So, that most likely has something to do with it. :(
 
Also, I strongly suggest you do the Video 4 Play hack.

Not only does it get you 3 additional games, BUT it does away with the daughter board (and all of it's bad sockets and possibly bad prom legs if it didn't use eproms) and also removes one of the two main sockets out of the picture.

It just takes a single larger eprom for code and 2 for graphics, and IIRC, 8 wires (16 solder points). http://www.arcades.plus.com/fourplay.htm

ALternately, there is a single Galaxian test rom you can toss in and at least see if you can boot, and if so, you know if there is any problem in the daughter card. http://ionpool.net/arcade/tech/galaxian_test_rom.zip
 
Okay. Problem partially solved. I realize after inspecting the board that someone has knocked off the chips at 4K and 4J (video ram?) and 8F and 8H (buffer?).

So, that most likely has something to do with it. :(

8f and 8h are alternate chips if b9 (I think my pdf is hard to read) is not used.

My board will not do much of anything and I going to bet on addressing problem and put in some 74ls138 chips in it to see what happens. If I rub my finger around where 8h would be I get pulses on 2 of the 3 138's. I really don't understand the addressing part of the boards but I do know there should be pulses on all 3 of the chips. I have verified my roms and they are good, voltage is good also +5.15 at the rom chips. So we will see. I had to disable the watch dog and solder the pads together.
 
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After further review 4K, 4J, 8F and 8H are all alt chips with corresponding chips in place. What I have seen on a few youtube videos is that the "artifacts" are actually the first part of the test pattern. So, my machine is getting to the test pattern, blitting that and then resetting to the black startup screen.

Would that make this a watchdog issue, a reset issue, something related to voltage? Again, sorry for my noob questions. Any help in the logic would be great and where to look would be fantastic!
 
It is failing to boot for some reason, could be RAM, ROM, logic etc etc

Also do not apply any hacks to the board until you have it working, in its original state you know it did work once, if you add a hack you lose that starting point.
 
It is failing to boot for some reason, could be RAM, ROM, logic etc etc

Also do not apply any hacks to the board until you have it working, in its original state you know it did work once, if you add a hack you lose that starting point.

+1

I am having some trouble with someone's hack and putting everything back, I still have some kind of addressing problems.
 
Sounds like it's going through the self tests but never finishing.

This can be dirty ROM legs, poor socket connections, bad ROMs, bad RAMs, etc... Watch the screen carefully when it goes blank to see if it flashes something up on the screen in the upper left corner such as RAM 1

RJ

Look at my post again. Did you check the pins on the ROMs? If they are the epoxy body ROMs with the tarnished/corroded pins then there's a VERY likely source of your problem. The ceramic EPROMs are much less likely to have that but still could have some corrosion on the inner surface of the pins.
 
RAM or ROM would make the most sense and seems to be what most folks are saying. I will have to test some more, but am fairly certain that's the problem. Trust that I want to do as little to the board as possible to keep it as original as possible.

Will post a follow up once I have this fixed.

Thanks for all your help!
 
Look at my post again. Did you check the pins on the ROMs? If they are the epoxy body ROMs with the tarnished/corroded pins then there's a VERY likely source of your problem. The ceramic EPROMs are much less likely to have that but still could have some corrosion on the inner surface of the pins.

Don't you hate being ignored?
 
Sorry. I posted before I read your post and finally reread the thread. So, anyway...

I would check the legs, but I have no clue which slots to check. Also, what is the best cleaning method?
 
As somebody else already stated, sounds like it's getting stuck and the watchdog is kicking in, which you can check by probing the reset pin on the Z80.

-Y
 
It is failing to boot for some reason, could be RAM, ROM, logic etc etc

Also do not apply any hacks to the board until you have it working, in its original state you know it did work once, if you add a hack you lose that starting point.

What happens if you rub your (dry) finger around where 8h would be? After you touch a good ground first to discharge any possible static charge.
 
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