Gallag board with one small problem

dbstallman

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Good evening, everyone.

I'm working on a Gallag board for a friend and it is working almost 100%. The only issue is with the main ship explosion. It is two top half sprites not a top and bottom half.

Here is a picture to show what I mean :
imag0822v.jpg


I have already verified the ROM data is correct and I know the data for the explosion is in the chip at location 6A on the video board. All of the character and ship sprites are good. I am pretty sure it is one of the TTL chips on the video board, but I'm not sure which. I figured I would ask the forums to see if anyone has seen this issue before to save me some time, otherwise expect and update to this thread in a day or two when I nail down the culprit to help anyone else with this issue.

Thanks,
Brian.
 
Good evening, everyone.

I'm working on a Gallag board for a friend and it is working almost 100%. The only issue is with the main ship explosion. It is two top half sprites not a top and bottom half.

Here is a picture to show what I mean :
imag0822v.jpg


I have already verified the ROM data is correct and I know the data for the explosion is in the chip at location 6A on the video board. All of the character and ship sprites are good. I am pretty sure it is one of the TTL chips on the video board, but I'm not sure which. I figured I would ask the forums to see if anyone has seen this issue before to save me some time, otherwise expect and update to this thread in a day or two when I nail down the culprit to help anyone else with this issue.

Thanks,
Brian.

any luck yet??
 
Not yet...

I found this repair log : http://www.jammaplus.co.uk/forum/forum_posts.asp?TID=14084&title=galaga-repair-log. Near the bottom of the post is
Gallag Info:

<!--[if !supportEmptyParas]--> <!--[endif]-->

Explosion drawing info:

<!--[if !supportEmptyParas]--> <!--[endif]-->

You'll probably find the bug explosions are doubled in the same way, but that's harder to see on-screen.

Fortunately there's not a lot to check, the sprite control custom IC 04xx doesn't handle the vertical sprite expansion so that won't need to be replaced.

So get out the logic probe and start testing�.

When the explosion is on screen check IC 2C pin 2 for pulsing, it's normally low and goes high when double size sprites are enabled. No pulse, replace the 74LS273 at 2C.

Next thing check IC 2E, pin 9 should be pulsing constantly, no pulse, then check pin 8. If there's pulsing on pin 8, replace 2E. No pulse on pin 8 that'll point to IC 4B ( 74LS86 ) needing to be replaced.

Finally... if all that looks good it's probably the 74LS153 at 1B not selecting outputs correctly, so replace that.

From my notes on the Galaga's I've repaired the culprits were 4B and 2C.

None of the pictures show, so I can't be sure if it is the same type of issue or not. I did find a couple of scratches in the area of the video board that the post talks about, but I have tested all the traces for continuity and they passed. The logic chips I have at those locations are different as well, so it might not be the correct part of the board.

I'm still looking, though. I haven't had any success with a logic probe yet.

Brian.
 
Not yet...

I found this repair log : http://www.jammaplus.co.uk/forum/forum_posts.asp?TID=14084&title=galaga-repair-log. Near the bottom of the post is

None of the pictures show, so I can't be sure if it is the same type of issue or not. I did find a couple of scratches in the area of the video board that the post talks about, but I have tested all the traces for continuity and they passed. The logic chips I have at those locations are different as well, so it might not be the correct part of the board.

I'm still looking, though. I haven't had any success with a logic probe yet.

Brian.

found this for you on a recent post so you might look closely at the customs on the video board.

http://forums.arcade-museum.com/showpost.php?p=2149318&postcount=6
 
If it were on my bench I'd check the address lines to the character ROMs. This looks like an address line's signal is incorrect. If it were the data lines out from those ROMs then you'd have horizontal lines.
 
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