Space Invaders Deluxe, jittering screen fixed, now there's a new problem....

DaveyPocket

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Space Invaders Deluxe, jittering screen fixed, now there's a new problem....

So if any of you had no idea what was happening here:

http://forums.arcade-museum.com/showthread.php?t=140362

I found the problem: Someone had swapped the crystal oscillators on this Space Invaders board, the oscillator was at the wrong frequency, causing the game to screw up. I installed the oscillator from my working board into that one, and the problem went away (I still had the ROM's removed). I got the horizontal bars.

After installing the game ROM's, the game powered up with garbage all over the place, except this time, it was stable. Also, when I take out ROM H and let it do the horizontal line thing, the horizontal lines have jittery pixels at the top of them.

Here's what I can tell you so far:

- Power supply is functioning properly
- No problems on reset line (It works fine)
- Sound board works
- CPU works
- Monitor works

Anyone know what the issue could be?
 
Good job in finding that crystal - I prob woulda never checked that! Incidentally, the reason it looked like a reset line problem, is because either a bad clock/crystal or bad reset line both leave the processor non-functional and produce the same looking screen.

Jittery pixels on the horiz bars is most likely a ram issue. You have a few choices as far as what to do from here:

1. Fire it up as-is, and ground pin 7 of each ram until you see a line appear through where your jittery pixels were. You just found the bad "pair" and somehow need to figure out which one is bad. They may both be.

(If you're looking at the board with the daughterboard to the left and the ram towards the back, each COLUMN of chips is a pair - they share pin 7.)


2. If you have a burner, and your original roms are 9316B's, download the test rom image, fry it to a 2716 rom, put it in socket H and replace whatever ram it tells you to replace until it fires up. There's a special layout you have to follow for the test rom - the codes it gives you are not actual chip position codes. See the very bottom of this page for more info:

http://www.marvin3m.com/video/seawolf.htm

Link to the test rom (you want the original):
http://www.outerworldarcade.com/arcade/space_invaders/space_invaders_test_rom.html

Last but not least - if you're ok with replacing chip sockets, do yourself a favor and just replace socket H now. I messed with a board for a couple days, getting junk/whatever, and just replacing the rom (and possibly the cpu) socket fixed it. Its been mentioned on here from a few people that the sockets on SI boards are prone to failure. You can just replace socket H and CPU sockets and do a single-rom-mod and not have to worry about the rest of them.

(For the single rom mod, do a search for "single rom mod" and my screename in the repair forum and you'll find it)
 
Jittery pixels on the horiz bars is most likely a ram issue. You have a few choices as far as what to do from here:

1. Fire it up as-is, and ground pin 7 of each ram until you see a line appear through where your jittery pixels were. You just found the bad "pair" and somehow need to figure out which one is bad. They may both be.

(If you're looking at the board with the daughterboard to the left and the ram towards the back, each COLUMN of chips is a pair - they share pin 7.)

I grounded pin 7 on the some of the RAM's which stopped the jittering lines, but when I replaced them, the issue did not go away. The garbage on the screen change but it is still jittering. I'm not sure if this moving garbage is being caused by the RAM or not, I might replace all of the chips and see what happens, or download the test ROM like you mentioned. Is there anything else besides a bad power supply, bad reset line, and bad RAM that could be causing moving garbage on the screen?

Also, the game sometimes started to play game noises randomly. I would leave it on for a while then hear the player explosion sound, or hear the UFO flying sound.
 
Remember the rams work in pairs - so if you replaced one and the same jittery lines are still there, you should replace the other in the pair.
 
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