Ms Pac horizontal movement jerky

debaser138

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I've got a Ms Pac that has developed an issue recently. It works fine when first turned on but then after about 15 minutes, the horizontal movement of Ms Pac and the ghosts is really jerky. Vertical movement is fine tho Ms Pac is sometimes not quite lined up with the maze.

Lawnmowerman's websites mentions the following:

Plays, But all character movements horizontally (left/right & vice versa) are jerky (Vertically okay).

Pin 15 @ 1F (74LS283) out of circuit.

I checked and that pin has continuity. I'm wondering if that chip is having issues once it heats up. Local shop didn't have any available so I haven't been able to swap it out yet.

Anyone have any ideas?
 
Hit the 7489 bipolar RAMs with some component cooler after it starts acting up and see if that returns it back to normal. You can get that in a spray can at any Radio Shack store... or you can use "canned air" if you turn it upside down.

There are 2 sets... you want to hit the set that is closer to the 5E/5F ROMs and not the ones in the sound circuit that are farther away.

RJ
 
Wanted to post a follow up as I finally got a chance to work on this board. I got some freeze spray and used it on a few of the chips I thought were the problem. Didn't make a difference. So I first replaced 3F. No change. Then I replaced 3H. That fixed the problem.

Thanks again for the info.
 
Looks like I spoke too soon. I had the game running all day yesterday and it was working great and then towards the end of the night it started doing it again. Powered it on this morning and it's doing it right away so it's not heat related. I've checked continuity on all the legs of 3H to their respective traces and everything looks good. I even tried swapping in new 7984's in both 3H and 3F and still no change.

I wouldn't think a bad 2114 RAM would cause this problem, would it?

Any other ideas what could be causing this?
 
I had a similar problem on a Ms. Pac I was fixing for someone. In addition to the 'jerky' horizontal movement, the sprites and maze had vertical lines through them, or looked chopped up. Does yours appear like that? It ended up to be a bad 74LS283 at 1F. Although its inputs and outputs were toggling, the problem went away as soon as I piggybacked a new 283 on top of it.
 
I had a similar problem on a Ms. Pac I was fixing for someone. In addition to the 'jerky' horizontal movement, the sprites and maze had vertical lines through them, or looked chopped up. Does yours appear like that? It ended up to be a bad 74LS283 at 1F. Although its inputs and outputs were toggling, the problem went away as soon as I piggybacked a new 283 on top of it.

Actually, I have had the screen go wonky just like you described a couple of times but it only lasts for a few moments.

I checked out both 1F and 2F to see if there were any bad traces and they checked out fine. Was going to try piggy backing a 74LS283 but I don't have any in my inventory and the local shop doesn't have them either. It's not very convenient trying to work on this board in the Ms Pac cab. I really need to setup a test bench soon for working on boards and monitors.

I'm gonna order a few of these and see if that does the trick.

Thanks for the info!
 
Just wanted to follow up on this as I finally got the part I needed and had a chance to work on the board. I replaced 1F and that fixed my problem. Ms Pac and the ghosts are moving normally again.
 
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