Help me fix my Pac-Man

Silkyfresh

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I purchased a beautiful Pac-Man cab awhile back. I now have the time to give it the attention it deserves.
Please help me get this beast running so i can reunite him with his wife.

Below is the picture of what happens when i turn it on.
 

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This is from http://lawnmowerman.rotheblog.com/#basictips


No Vertical Sync - lines and colored block out of sync. No game play.

Replace 2R & 2S (74LS161)


Main page: http://lawnmowerman.rotheblog.com/

You probably already know about this page, but just in case. Lawnmowerman's page is awesome for Pac-Man repair tips.

Also, basic stuff that often works:
- Super carefully remove and then replace all socketed chips to re-seat them.
- Look for burned areas on the edge connector contacts.
- Visually inspect the edge connector (burns, bent contacts, broken wires at the solder points).
- Check across one the big caps (C2 or C3) to see if you have good 5VDC.
- Inspect all electrolytic caps: signs of leaking? bulging? electrically good?
 
Forgot the most obvious thing: Inspect the fuses and fuse block at the bottom of the cab near the transformers. These fuse blocks fail often, developing high resistance on their contacts that creates voltage drops that lead to game malfunction.
 
If you want to buy a working board I just fixed 3 this weekend.
One for 115 shipped to usa
 
This is from http://lawnmowerman.rotheblog.com/#basictips


No Vertical Sync - lines and colored block out of sync. No game play.

Replace 2R & 2S (74LS161)


Main page: http://lawnmowerman.rotheblog.com/

You probably already know about this page, but just in case. Lawnmowerman's page is awesome for Pac-Man repair tips.

Also, basic stuff that often works:
- Super carefully remove and then replace all socketed chips to re-seat them.
- Look for burned areas on the edge connector contacts.
- Visually inspect the edge connector (burns, bent contacts, broken wires at the solder points).
- Check across one the big caps (C2 or C3) to see if you have good 5VDC.
- Inspect all electrolytic caps: signs of leaking? bulging? electrically good?
Im assuming these are the chips i need to replace ?
 

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Those could very possibly be the problem. They are the ones mentioned on LM's page. Can you check to see if the chips have 5V on pins 16? Do you have an O-Scope? Probably should download the datasheet too.

But, be sure to try all the easy stuff first! I wouldn't desolder chips until I was sure it was necessary.
 
Those could very possibly be the problem. They are the ones mentioned on LM's page. Can you check to see if the chips have 5V on pins 16? Do you have an O-Scope? Probably should download the datasheet too.

But, be sure to try all the easy stuff first! I wouldn't desolder chips until I was sure it was necessary.

I dont have an O scope. I do have a multimeter i can check the pins in the board.

I am getting 2.5v across 2S and nothing across 2R
 
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That seems like a solid clue. Something may be pulling the voltage down on the board, but it may or may not be these chips. You may be looking for a shorted component.

Are any the chips on the PCB hot to the touch (like they're shorted and pulling way too much current)?

You may try to remove all the socketed chips (with the game off of course) and then turn it on and see if the voltage comes back.

Also, be sure to check that you're getting a solid ~7VAC coming in. Don't forget to check the contact integrity of the fuse clips. Remove and re-seat all the fuses.

Bad contact at the fuse clips (or at the edge connector) will create a high source impedance situation. The voltage will look OK unloaded, but will be pulled down when you connect a load.
 
That seems like a solid clue. Something may be pulling the voltage down on the board, but it may or may not be these chips. You may be looking for a shorted component.

Are any the chips on the PCB hot to the touch (like they're shorted and pulling way too much current)?

You may try to remove all the socketed chips (with the game off of course) and then turn it on and see if the voltage comes back.

Also, be sure to check that you're getting a solid ~7VAC coming in. Don't forget to check the contact integrity of the fuse clips. Remove and re-seat all the fuses.

Bad contact at the fuse clips (or at the edge connector) will create a high source impedance situation. The voltage will look OK unloaded, but will be pulled down when you connect a load.
I am getting a solid blue screen now. I have no idea how i have been very careful. I'll go ahead and check the fuse block again.

Update: Voltages coming out of the fuse block are bang on.
 
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that first pic looks like horizontal sync needs to be adjusted. K4600, right???
 
Replace the fuse blocks! I wont even power up a Pac game without first replacing the fuse blocks. There is seriously no reason not to, its cheap and easy to do and you cant tell if you're current ones are bad just by looking at them (hint: they probably are)
 
I guess you're into the realm of system debug now. Wish I could help more. There are many possible causes for your problem. Seems like contact integrity (anywhere there is a connection in the machine) is always a potential problem with old games like this.

If you feel like voltage is good going to the PCB, then it may be a bad component. Follow the clues. Good luck!
 
Alright fellas!!!
I found a pin that wasnt sitting in the Z80 board. Pulled it out rebent the pin. NOW pacman is playing blind sounds and all. New screen now.
 

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