My Pac Man has died

Torin

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Got my Pac man up and working fine yesterday until I was adjusting the leg levels from inside the cab and must have bumped something and I heard a low buzz through the speakers for about three seconds and then the monitor went blank. The only thing I can think of is that I had a loose ground on the board (the big yellow flat cable) and one other loose ground from the isolation transformer (a brown and yellow wire). I hooked up the pac for the first time and don't know where the brown and yellow ground goes. Any ideas on where to start?


All lights, marquee etc still work fine.
I hear the hum through speakers still.
Game does not play blind.

There is current to the board and diodes from what I could tell from my multimeter. The fuses look to be good but I don't really know how to test those. Any advice would help.

I am new to the multimeter and do not know really what to do or check next.

Anyways, I appreciate any help on this.

Torin
 
If you can't hear the game playing blind, then chances are your monitor is okay. Definitely start by checking out the fuses. Does your meter have a continuity check feature? You'd want to use that to test your fuses.
 
I checked all fuses with continuity reading and all are ok.

The monitor comes on fine. I agree that it is most likely not the monitor.

I checked the VAC on the transformer and it read 115 VAC.

Wonder if I fried my board?
 
My condolences

5144190248_60db91aaf6.jpg
 
Re: My condolences

Yeah, thanks. Any ideas to what I can check on the board itself?
 
My Pac Man Has Died

I'm not too familiar with testing voltages in general but I took readings from the pcb's edge connector. I didn't find readings on most of the edge connectors except for 5 and 6 which read 7.8vdc. I could get readings on all capacitors, diodes etc. I got about a 2.5vdc readings on the roms. I looked for loose solder and couldn't see any.

Any other ideas are greatly appreciated.


Test the voltages on the board. You are looking for 5vdc and 12vdc.
 
I'm not too familiar with testing voltages in general but I took readings from the pcb's edge connector. I didn't find readings on most of the edge connectors except for 5 and 6 which read 7.8vdc. I could get readings on all capacitors, diodes etc. I got about a 2.5vdc readings on the roms. I looked for loose solder and couldn't see any.

Any other ideas are greatly appreciated.
Pac Man actually takes in AC voltage to the logic board and then rectifies the +5 on the board. I would double check the readings at the edge connector with your meter set to AC volts. The transformer that outputs the AC voltage doesn't seem prone to fail so if the fuses are good, I would suspect it's a problem on the board, but definitely verify that the AC voltage to the PCB is there and correct. I haven't spent a ton of time working on Pac-Man, but I tend to check the +5 right at a TTL 74XX series chip. There may be an easier place, but you should almost always have a TTL chip you can take the reading from on a pcb.
 
Pac Man Has Died

Thanks for your help guys. I will test the voltages again tonight using AC. I should have thought that one out a little further. Thanks for the link to the manual as well. I'll post back when I get the readings.

Torin
 
Pac Man has died

Pac Man actually takes in AC voltage to the logic board and then rectifies the +5 on the board. I would double check the readings at the edge connector with your meter set to AC volts. The transformer that outputs the AC voltage doesn't seem prone to fail so if the fuses are good, I would suspect it's a problem on the board, but definitely verify that the AC voltage to the PCB is there and correct. I haven't spent a ton of time working on Pac-Man, but I tend to check the +5 right at a TTL 74XX series chip. There may be an easier place, but you should almost always have a TTL chip you can take the reading from on a pcb.

Ok. I took the readings the correct way. Thanks Guru.

The pcb is giving me a reading of 11.4vac at pin W but nothing at pin X. It is giving me 6.2vac at pin C but nothing at pin D.

All the roms are testing at 2.65vdc.

What does this tell me? Any ideas to help me move forward is appreciated.

Torin
 
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you have a bad fuse or fuse holder on one side of the 12vac, or your transformer has crapped one side of the 12vac but I doubt that.
 
Pac Man has died

You were right, I had two blown fuses. I have fixed them and now get correct AC readings at the board but still no pac man.

Only a blue screen with voltage hum.

I'm at a loss. How do I narrow it down from here.

Thanks again.


you have a bad fuse or fuse holder on one side of the 12vac, or your transformer has crapped one side of the 12vac but I doubt that.
 
Big white resistor on the top left corner of the board right above the heat sink. Measure the DC voltage on both sides of it and see what you get.
 
Pac Man has died

Big white resistor on the top left corner of the board right above the heat sink. Measure the DC voltage on both sides of it and see what you get.

2.9vdc on the left
8.0vdc on the right

Same readings on both solder and component side.

That thing gets really hot.
 
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Your Regulator is bad (D44VM on the heat sink right below that resistor) You can prove this by putting a jumper wire across that big resistor, and the game should boot up.

If the game boots up, you can replace the D44VM with a TIP31. (Make sure that you use heat sink compound, Mica, and the little spacer for the screw)
 
Your Regulator is bad (D44VM on the heat sink right below that resistor) You can prove this by putting a jumper wire across that big resistor, and the game should boot up.

If the game boots up, you can replace the D44VM with a TIP31. (Make sure that you use heat sink compound, Mica, and the little spacer for the screw)


Wow, amazing help. Thanks Dokert. I jumped the wire from one end of that big resistor to the other and I finally got something back on the screen! Although it was a bunch of O's and F's and 7's and 3's etc. I will definitely replace D44VM. What do I make of the jumbled screen? Thanks again!
 
Put it into test after you have replaced the D44VM and see if it tells you anything. Might be the Z80 is not seated good, or is bad, or has a bad socket. Don't know, can't see what you are seeing.
 
My pac man has died

Put it into test after you have replaced the D44VM and see if it tells you anything. Might be the Z80 is not seated good, or is bad, or has a bad socket. Don't know, can't see what you are seeing.

Well, I was finally able to get back to this and replaced D44VM. I now get constant current through the white transisitor at: 6.7Vdc on both sides.

Now, at least I get the following pictured jumbled screen. I have felt the board for hot spots and find that D7 and D8 both get pretty hot.

I tried putting it in test mode, but I get the same jumbled results

Dave or anyone else, do you have any ideas where to go from here?
 

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