Tapper plays with wrong FG sprites

gwarble

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Hey all,
Hoping to dig into this problem a little more so I figured I'd reach out to the experts first...

My Tapper is working well except for one problem its had since I got it... some of the foreground sprites/characters/items are displaying the wrong sprites. Some guys are from the wrong level, sometimes there will be a pair of legs in place of a character...

instead of being left a tip of cash, you're left a cheerleader's arm with pom pom, thats fun...

So reading around the MCR and Tapper books, and some threads on here, seems sprite issues are common but I haven't seen this particular problem. Its not intermittent either, its always the same wrong sprites... So i'm thinking one of the address lines is stuck hi or lo when deciding what sprite to access, maybe some 74LS... chips that control access to the video ram or FG rom...

Anyone have any suggestions on what I should be looking/testing for? Board passes visual inspection, all socketed chips removed, cleaned, reseated... all ROMs on the MCRIII Video Gen board were pulled and verified good, and interconnect cables are new and all headers for them re-soldered.

Thanks in advance
- Joel
 

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Last edited:
Hey all,
Hoping to dig into this problem a little more so I figured I'd reach out to the experts first...

My Tapper is working well except for one problem its had since I got it... some of the foreground sprites/characters/items are displaying the wrong sprites. Some guys are from the wrong level, sometimes there will be a pair of legs in place of a character...

instead of being left a tip of cash, you're left a cheerleader's arm with pom pom, thats fun...

So reading around the MCR and Tapper books, and some threads on here, seems sprite issues are common but I haven't seen this particular problem. Its not intermittent either, its always the same wrong sprites... So i'm thinking one of the address lines is stuck hi or lo when deciding what sprite to access, maybe some 74LS... chips that control access to the video ram or FG rom...

Anyone have any suggestions on what I should be looking/testing for? Board passes visual inspection, all socketed chips removed, cleaned, reseated... all ROMs on the MCRIII Video Gen board were pulled and verified good, and interconnect cables are new and all headers for them re-soldered.

Thanks in advance
- Joel

Logic probe... I would start poking around at A12, A9 and A10. Those appear to deal with the ROM Addressing.
 
Thanks

That makes sense... i can't see how I'll work on these boards running without laying them all out without the metal plates and making a test harness to run it outside the cab... bummer

its probably easier/faster to just change out those addressing chips... hmm


Edit:
A12: 74LS273
A10: 74LS86
A9: 74LS86

I'm pretty sure I can piggyback the 74LS86, maybe the 273 also if I'm lucky
 
Last edited:
Thanks

That makes sense... i can't see how I'll work on these boards running without laying them all out without the metal plates and making a test harness to run it outside the cab... bummer

its probably easier/faster to just change out those addressing chips... hmm


Edit:
A12: 74LS273
A10: 74LS86
A9: 74LS86

I'm pretty sure I can piggyback the 74LS86, maybe the 273 also if I'm lucky

Shot gun approach might work, but I would build a harness... ( I might need to depending on what's wrong with my Tapper)...
 
i probably should too, but quick and dirty might buy me time until I get a more serious problem (knock on wood)

looks like I might be able to unhook enough of the harness from those plastic clips to get it out the back of the cabinet... so maybe a carefully placed table behind the cabinet and I can, I'll see what I can do after dinner
 
Yeah i don't think thats going to work... I got those 74ls86 and 273 chips on order, so when they arrive i will try piggybacking them, replacing them, and ultimately if i have to i'll get to work on an extension harness or a test bench harness

Thanks for the initial guidance, i'll log any progress i make or don't make here

And if anyone has any other suggestions for possible culprits i'm all ears
 
unfortunately not yet

i did try piggybacking those three chips mentioned above, with no change. One of these days I will swap them for real and see, otherwise I gotta build a test harness so i can test and probe the boards while out on the bench :(

do you have a similar problem?
 
I don't think so, but I can't be sure. I just got one and only played it for a minute when I was checking it out. Seems like it could eventually happen though, and I like having contingencies. Would a new ROM set fix this and are they even available?
 
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