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Having an issue with a Pac-Man board...


PacManPlus
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Hey Guys:

 

I was hoping someone could help me. I've acquired a Pac-Man board that doesn't boot. As soon as I apply power, I get the below screen:

post-1787-0-16769900-1453675023_thumb.jpg

 

It never changes and never goes away, no matter what I do. I have tried:

 

- Replacing 5E, 5F, and all four roms of row 6

- Replacing the Z80

- Replaced all 6 RAM chips at 4K - 4R

- Replaced the VRAM and the Sync Controller

 

I've even powered on the board *without* any eproms in Row 6 or the Sync Controller, and got the same exact result.

 

I have looked at NUMEROUS sites (mike's arcade, lawnmower man, etc.) Nothing has this exact scenario, with something I haven't already tried.

Before I start measuring voltage levels, has anyone seen this before?

 

Thanks,

Bob

Edited by PacManPlus
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Thanks - I actually saw that post...

 

It's not exactly the same as his issue, as my screen stays static. He said he swapped something and the screen changed garbage...

 

I'd still like to try the +5 Volts on the reset line on the CPU and see if anything changes though...

I guess I need to measure voltage. God I hate doing that.

 

Thanks,

Bob

Edited by PacManPlus
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I was messing with some chips yesterday. God, nothing I do changes anything on this thing. Some of the voltages seem ok, the +5 is alright. Maybe this board is just hosed? After going through a couple of boards that were *completely* dead a while back (i.e. no video or audio - nothing) this seemed so close... :mad:

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Looks like it's stuck at its initial boot sequence and not getting past it. You try cleaning and diddling the service switch right inside the coin door? Replace the large axial/can filter cap(s)? That board looks far from being totally hosed to me. You're almost there...

 

PM incoming with info of a guy that helped me out with a Pac-Man board recently.

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No good on the large filter caps. :( Also, the board isn't in a cab at the moment so it's not the service switch. Also switch 8 is off. ;)

 

I hate being this close. I'd rather the board have been completely dead.

I've now also replaced:

- The two large can filter caps

- The cap at C51

- 5M

- 2F

- 1M

 

No change at all.

 

I give. I'll see what this guy will charge for fixing the board. If it's not worth it, it goes in the scrap pile.

Thanks,

Bob

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Ok, I just tried something.

 

WITHOUT the Z80, and WITHOUT the Sync Bus Controller, I powered it on. I get the EXACT same screen. I'm starting to think it may be a CPU issue. However, I've already swapped CPUs, and The Sync Controller. Also, I've inspected the sockets and traces (on the opposite side as well). Nothing looks broken, bent, or out-of-place.

 

This is driving me crazy.

 

What made me do this, is I saw this on the internet from Jrok (pretty famous name around the Pac boards) :)

 

"If the display is completely static and just showing random garbage, it's very unlikely to be just the RAM.

Here's the rationale for that.... because, right after a dead z80, this points to a problematic sync bus controller. If that goes bad/missing/bad socket etc. the z80 will never be able to write out to the video RAM so the system appears frozen. There's also the possibility of 7M ( 74ls139 ) being bad but that, in my experience, is less likely than a problem SBC.

When the SBC is working and you have bad RAM you can normally see the system clear the screen, or attempt to, and start the repeating patterns of the RAM test being written on-screen and not just random static characters.

- James"

 

My next move is to desolder 7M from both boards (my old one I am using for parts) and this one, and swap those... Maybe tomorrow. I'm done for the night.

BTW, every time I swap a chip, I install a socket. I'm all for making things easier.

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Side note, I was able to get my hands on a working board.

 

Not one to let things go, I pulled out the Sync Bus Controller of the working board, got the exact same screen as the bad board.

Replaced it, pulled out the Z80, also got the exact same screen.

 

So now, it's definitely either the Z80 or the SBC area on the bad board. I've already replaced both, so it isn't the Z80 or SBC itself. Pulled off the socket for the SBC, don't see any broken traces or whatnot - on either side.

Going to de-solder the Z80 socket to see if there are any. Last resort.

 

Can't be anything else, right?

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Replaced socket. While it was off, looked for any broken traces. Found none. Put new socket on, got same issue.

 

Board, you've completely kicked my ass.

 

In other news, I purchased a Pac-Man cabaret for $500 shipped. Needed wood work, so I laid it down in the garage to start working on one side (on a rug). We had a major storm yesterday, and water got into the garage. The side of the cabinet that was facing down and some of the boards attached to it got soaked, and everything swelled. $500 down the drain.

 

Sometimes, I feel like Charlie Brown. :mad:

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  • 2 weeks later...

Update:

 

Someone was selling an unpopulated board on e-Bay "as-is" for $20. I took a chance and bought it.

 

I populated it with the ROMS, Proms, Sync, and VRAM controller.

 

At first, I got white interference lines all over the screen, and no game. I was very bummed for having spent now *more* money on this.

As I watched the screen, I noticed that it might be a RAM issue. I replaced all 6 video RAM chips, and suddenly everything is now working.

 

I'll use the "bad" board for parts, being as I basically replaced almost everything in it already.

 

Bob

Edited by PacManPlus
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  • 7 months later...

Hi Bob, I've got the same problem with my pacman. Video is here: https://youtu.be/L7qSNZ1qjn8. The screen then goes black after about 30 sec and there's a clicking sound coming from the speaker. I'll try replacing the 6 video RAM chips, but could you please tell me where they are located? And where would be a good place to get replacements?

Pacman is only my 2nd game so I don't have a lot of experience yet. Thanks! Doug

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