Baby Pac-Man
Bally, 1982This thing has been a challenge. I realize that this is probably more of a "Video Game" question, rather than a pinball question.
Had the Vidiot board working perfectly for a few minutes. Then this happened. Just random garbage comes up on the screen.
The Vidiot goes through the 10 flashes. The TMS9928AN has been replaced. No change. I'm out of ideas, and can't find anyone ever having this issue before.
Your cpu is working good too?
The sockets on the vidiot board are good?
No acid on either board?
Just giving ideas
Try the video self test button. Do you get the communication test screen? Press the test button again. Do you get the color bar test on the screen?
For all the socketed chips, are all the legs clean and untarnished? Any damage around the sockets from prying up chips improperly?
Maybe a bad video ram chip that isn't being picked up by the boot test?
I don't think the video amplifiers can fail this way, but maybe a problem with u17 or u18?
Maybe garbage data is being fed in to the video processor somehow?
Maybe a broken PCB trace somewhere? hold the board up to a bright light and carefully inspect it.
Quoted from jj44114:Try the video self test button. Do you get the communication test screen? Press the test button again. Do you get the color bar test on the screen?
pressing the self test button does nothing
Quoted from gameover1173:Your cpu is working good too?
The sockets on the vidiot board are good?
No acid on either board?
Just giving ideas
Quoted from ForceFlow:For all the socketed chips, are all the legs clean and untarnished? Any damage around the sockets from prying up chips improperly?
Most of the sockets have been replaced. I did this to go from dead to 10 flashes. I admit one of the ROM sockets has not been replaced, but I would expect that it wouldn't go through the complete flash sequence. The legs on the ICs have been cleaned.
MPU is a new Alltek. MPU connectors and pins have been replaced
I did learn something about the pervasiveness of battery damage. Visually, the ROM socket pins looked fine, but replacing them fixed the original boot issues.
Quoted from ForceFlow:Maybe a bad video ram chip that isn't being picked up by the boot test?
I don't think the video amplifiers can fail this way, but maybe a problem with u17 or u18?
Maybe garbage data is being fed in to the video processor somehow?
I really think you are on to something here. I really believe the issue is in the Video processing section. I was wondering if anyone has seen a failed video processing crystal that might cause this? But then again, the chances of a failed crystal are pretty minuscule. But that's me! I seen to get all the odd-ball problems that occur once in a lifetime for everyone else.
So, Video RAM first. Will report my findings.
Quoted from songofsixpence:I really believe the issue is in the Video processing section.
That's what I was thinking.
I've perused some pacman board repair guides which have helped a little with some fundamentals of video arcade board concepts since those boards are exceptionally well documented. It might be helpful to seek some of those out, especially since they're from the same time period and manufacturer.
Maybe one of those pacman guides has documented a similar failure that can help narrow things down to the type of failure it might be (ROMs, processing, RAM, amps, etc)
Quoted from songofsixpence:Most of the sockets have been replaced.
Another thought. The traces this board are pretty fragile, and it's pretty easy to lose pads and have them break off from traces.
So, I'd definately suggest holding the board up to a light, like I mentioned earlier.
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Wharton, NJ