Joust crashes when too many enemies onscreen

swap ram 21 with 31 or 11, does the error carry? I mean you could just have a bad ram, I don't know what you've tried already.
 
Yeah, I've already confirmed all my RAM is good. It's something else on the ROM board not being able to talk to the MPU board correctly.

I swapped all my Joust ROMs onto my Robotron ROM board and the game ran perfectly with an All Systems Go message.
 
I had a similar problem with my Stargate machine, Game was working fine, then I upgraded to 4164's from Bob Roberts. Game was fine for a month or so, then began to randomly 'artifact', freeze, or reset. Since the RAMs were only a month old, I mistakenly assumed they were good, and went about replacing every socket/header/connector/ribbon cable on the whole set. This crap went on for over a year. One day, for the hell of it, I ran the RAM test. Sure enough, after running the RAM test for almost an hour, it flagged a bad RAM. I swapped the RAM and the game has been fine ever since. I know you mentioned that the RAMs are good, but how long did you run the RAM test for??
 
It "detects" an error with RAM 21 immediately upon bootup and immediately when running the RAM test. The thing is, none of the RAMs are bad. I've swapped them all around and swapped the entire set with my known good RAMs from Robotron, and it's always RAM 21 or very rarely RAM 22. I realize that the error moving on its own suggests a power issue, but I have solid voltage all the way through. This error has been present since before I got the game, because some past owner soldered in a different socket for that RAM, and thinking they did a bad job, I replaced that socket. And as I mentioned before, it runs perfectly with a different ROM board.

I also tried swapping in just the special chips from Robotron a long time ago and there was no change.

I think I'm going to go ahead and just replace the rest of the logic chips that I can on the ROM board since replacing the 7474s improved it so massively.
 
If the RAM error stays with the location even though you swap RAM, I would look in the associated circuitry directly connected to RAM 21 and 22.
 
It's a good idea, but since a different ROM board doesn't report the error, I'm inclined to think it's still something wrong with the ROM board.
 
Interesting thread, I assume you have check out the eproms.
Normally, Eproms going bad are not an issue due to the fact the little windows are covered.

Take a close look at the ribbon cable on the joust pcb board. During the Life of the machine sometime a field tech will press on the ribbon cable that is attached to the Rom pcb without support. This flexing can cause the traces to crack and cause odd issues.
A microscope is useful for checking this problem.

I assume you check out the little bypass caps on the rom PCB board. Rarely do they go out and if the do go out they normally don't cause a great issue.

I wonder if the eproms were burnt before your problem showed up? Eproms do have a speed rating. Slow accessing eprom?
 
The EPROMs are all original and they all test good. I thought about the little filter caps as well but I can't see anything wrong with them.

I actually replaced the ribbon cable when I got the machine because it was in bad shape and I thought it would be the cause of the issues but it wasn't.

Almost everything on the board has been reflowed at this point. The special chips, PIA, and ROMs all have new dual wipe sockets. All of the pin connectors have been replaced with modern ones with square pins. The electrolytic capacitors on the board have been replaced.
 
Have you checked the connection around the pad ( Dough nut ) to the trace itself?

There a sinstar that is being repaired with that issue.

I assume you replace the dual header pins on the main PCB board..

Can you check the small bypass caps with a meter and check for shorts?
 
Taking Charles' advice, the next thing I swapped out was the two 7474s on the ROM board. The graphics copying problem is vastly improved. It only started leaving copies of enemies onscreen around wave 8 or 9 and it didn't crash, so I was able to actually finish a game.

I had to swap them out with 74LS74s because it's what I had available. Do you think it would be better to replace them with 7474s instead? I socketed them in case thos might happen again.

I still get RAM error 21 when I boot the game with this ROM board, so maybe there's another problem chip to replace?

Awesome, glad it helped some!
 
Bizarrely, according to the logic tester in my ROM burner software, both of those 7474s are good. The 7411 I just pulled tests bad however.
Maybe one of the 7474s was just bad enough to cause trouble but still let the game run?
I'm going to get non-LS versions of these chips to see if stability improves.
It's still having some problems, like (very rarely) drawing the box around enemies or putting the high score screen border around the playfield.
 

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Bizarrely, according to the logic tester in my ROM burner software, both of those 7474s are good. The 7411 I just pulled tests bad however.
Maybe one of the 7474s was just bad enough to cause trouble but still let the game run?
I'm going to get non-LS versions of these chips to see if stability improves.
It's still having some problems, like (very rarely) drawing the box around enemies or putting the high score screen border around the playfield.

Are you testing with a Logic Probe or a scope?

If you're testing with a Logic Probe and have access to a scope, use the scope. A logic probe could show it pulsing between High and Low even if the voltages don't get near their maxes (0 for Low and 5V for High).

For example, I had a Missile command that was having an issue with the Track Ball. Logic probe showed the input and output of a chip pulsing. So I'm thinking the chip is good, but there really wasn't anything else it could be.

Hooked up the output to the scope and saw that the "High" was only like 3.5V (don't remember the exact voltage, but close enough). Enough to trigger the Logic Probe, but not high enough to show high on the downstream chip. Replacing the chip fixed the issue.
 
Unfortunately I don't have a scope. I was testing the chips after I took them off the board since I had replacements ready.
 
The testers don't tax the chips like the game circuit does so it is possible for a chip to test good but not function in circuit.
 
Bizarrely, according to the logic tester in my ROM burner software, both of those 7474s are good. The 7411 I just pulled tests bad however.
Maybe one of the 7474s was just bad enough to cause trouble but still let the game run?
I'm going to get non-LS versions of these chips to see if stability improves.
It's still having some problems, like (very rarely) drawing the box around enemies or putting the high score screen border around the playfield.

which 7474s did you change? the row 7 ones you can use LS or HCT or whatever, but everywhere else you might have problems with anything but 7474s. I think you were talking about the rom board before so it's probably those?

try removing decoder 6 and run the game. (note it'll just be color bars) it'll probably dig up a lot of bad rams then. this is some weird little life hack thing I stumbled upon a couple months ago.

the POST of the game taxes the rams harder than normal operation, it's plausible in some instances where they'll show bad in the POST (like a 1-2-1) but the game will still work. if you have any suspect/error rams remove them and ensure the outer legs aren't bent like 45 degrees from improper past removal. they'll make poor contact in single wipe sockets like these games came with. also make sure there aren't any folded legs or other assorted silliness. I had a board where the outer 3 pins by the ground were all compressed together. (???)
 
Yeah, running the game with my Robotron ROM board (with the Joust ROMs on it) reports no RAM errors so I'm considering it highly likely that my ROM board is the culprit. I've swapped the RAMs all around and even tried my known good 4164s in it and it's always been the same. Also, I actually replaced the socket for RAM 21 early on since I thought that might be the problem.

Good to know I just need to be running plain 7474s on the ROM board. I'm ordering some now.
 
you try reseating the Special Chip sockets and make sure the sockets are good? the pins can just break off inside those. I would pull the chips and then carefully pry up the plastic housings and inspect the pins, try wiggling them back and forth. if you chop a tree down, it's time for a new socket.

I would think if the 7474s were bad on the rom board it wouldn't function well. I got one awhile ago where the 1-3-1 error was caused by the rom board and I was strangely fortunate their board wasn't a match with the others and I just subbed it for another one I had. I never looked further into it, but it wasn't any of the lower chips by the Special Chips that were bad, so I imagine it's a 7474.
 
Good to know. I actually went ahead and replaced the old special chip sockets a while ago just in case, since I know they can be a weak point.

This ROM board and MPU board don't match the serial of the cabinet and the other PCBs so who knows what this poor game has been through. It was a mess when I picked it up.
 
This ROM board and MPU board don't match the serial of the cabinet and the other PCBs so who knows what this poor game has been through. It was a mess when I picked it up.

In that case you could pick up another ROM board and put this one out to pasture.

But you have replaced nearly everything on it so it'll be brand new once you're done!
 
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