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Choplifter bootleg parallax scrolling issue


Lurch666

Question

I have a choplifter boot I am repairing and I have most of the issues fixed but can't seem to sort the parallax scrolling of the ground.It glitches around in a random manner.

Does anyone here know what part of a choplifter board handles this?

 

Picture of the pcb without the daughterboard:

 

 

2018-02-24 10.43.47-1.jpg

 

 

Thanks.

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Yep the problem is that I'm not looking for a missing signal but a corrupt one so it's hard to tell from my scope if I'm getting the correct data coming from a chip.

I'm poking around the board (focusing on fujitsu chips at the moment ;) ) trying to stumble on the problem.

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Yep the problem is that I'm not looking for a missing signal but a corrupt one so it's hard to tell from my scope if I'm getting the correct data coming from a chip.

I'm poking around the board (focusing on fujitsu chips at the moment ;) ) trying to stumble on the problem.

 

I would not specifically say that, logic is formed quite specifically you can tell from weak signals to dirty signals all with a scope I would easily use it over a probe every time...

Since its background scrolling I would maybe (without looking at any schematics at all) find the ROMS that hold the data and work from there... Check the ROMS are all good and the sockets are 100% (press on them or pry them a bit while the game is running and look at the screen)

Also you may want to look at the shift registers (usually 74LS164, 175, 166 but may be others) https://en.wikipedia.org/wiki/List_of_7400_series_integrated_circuits

And the last thing to check in this area is any ram dedicated to the background, of all things ram is often the only component complex and dynamic enough to cause randomness in errors where as specific logic always faults the same way.

 

Have a look at mame and see where the ram regions are or the locations of roms etc, check for damage or corroded tracks or components bent over etc...

 

There are many other tricks to try, you can piggy back spare ICs or use a pull up or pull down probe to force specific inputs or outputs and see the reaction on the screen...

Anyway there are heaps of possible things, the chances of fixing are in the details of the fault, your description is just not specific enough for anyone to really say much about it, how a fault behaves onscreen as well as the shpe, and changes that happen when cold goes to hot etc all play a part in diagnostics....

Video is the best way for others to at the very least set you on a closer path to glory ;)

 

Good luck....

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Have replaced most of the memory as part of fixing the sprite problem and have replaced the rest as part of this fix.

I don't think this is a rom problem as all the rest of the scrolling background is fine and the problem gets worse as time goes on.

That made me think of a chip heating up but can't find any warm chips connected with this issue.

Have scoped various parts of the board and used a video probe and changed a few chips but with no change to the problem.

Piggy backed lots of chips (especially the fujitsus) and I'm still checking different things but I was hoping someone has come across a similar problem that would narrow this down.

 

Thanks for the idea of looking at the shift registers-will check them next.

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That video helps heaps!

I would not look at the ROMs as the data all looks clean I would look at background scrolling circuits, it would not surprise me if some sort of counters or shifters in logic IC's are involved to make the parallax scrolling and the chain is broken somewhere.

It does not look like ram either as the issue is with a layer of the scrolling....

You did say you noted when cold to hot the issue changes, with that you can get freeze spray or (inverted) compressed air in a can and spray IC's till they frost up and note sudden changes and they when found can be probed with the scope more closely for spikes of data that match the jumps you see on screen.

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