Odd Galaga graphics issue...

adamzero

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Hey guys-

My Galaga has this strange little glitch happening that I'm thinking is coming from one of the chips on the board (might need a re-seat?) rather than the monitor. It's flickering horizontal lines that pop up for a second or two and only seem to branch off from the player ship (explosion/death mainly), shots fired (good and bad guys), and sometimes the aliens themselves. On-screen text & background scrolling stars have no issues.

They seem to appear more on the left sides of the things noted above, but sometimes a little on the right, here & there. But mostly extending left. Also, it seems to get worse the longer the game is on.

I'm guessing this is chip-based, as the explosions/bullets/player ship/aliens are probably generated on a chip different than the background/text?

Can someone tell me which chip to re-seat, or should I just reseat them all? Checking the voltage & re-seating the chips were going to be my first order of business, but does anyone have any other suggestions or have seen this before? Pics attached, sorry they're a tad blurry, I extracted them from video...
 

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Bad resistor pack down near the video RAM... Bad RAM chip... bad 74LS368 clock buffer... Seen all three of those cause that symptom.
 
I'm one of the few (if there are that many) that will touch them. They take a shit ton of work to rebuild.
 
I've run across a couple of bad 8xx chips. Outside of that, they are pretty robust - excepting for snapped pins. ;)

Acid damaged Pole Position or partially stripped Dig Dug boards are great sources of customs.
 
CManic, if my level of skill with these doesn't do the trick, do you work on Galaga boards?

I have several of the video boards that are working if you decide to go that route but I would rather trade.

I have had a few bad buss driver chips bad (08xx) but have found many many more clock chips bad (07xx). A single bad line on a chip or trace will do that and if you look real close on the parts side of the video board you will see many of the lines (traces) go right near the soldered pins of the chips (4m and 4h comes to mind for some reason but there are more). Look at the traces and check the ribbon cable. If you have the flat resistor packs and crappy sockets, get a renew kit (money well spent). Even if you just do the resistor packs, They are a source of many of the problems I have found.

Since the problem gets worse with time/heat try some freeze spray/component cooler and spray a few chips, while on and look for any changes. This only works with chip and connection issues and not for trace issues.
 
I wouldn't waste my time on troubleshooting a Galaga board until the resistor packs and sockets are redone.
 
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