Pac-man upright sound issues.

Michaelthurston

New member
Joined
Sep 30, 2012
Messages
338
Reaction score
2
Location
San antonio, Texas
Hey there guys, so I recently bought a Pac-man Cab from arcadefr34k, and It was non-working. When he originally bought the machine, everything worked, including sound, he sold it to me when the game stopped booting. It's working now, but the sound isn't. Back when I was trouble shooting, I removed the audio amp to see if it was bad, because I had fuses blowing. I lost the amp, but reordered an LM377N. It just came in today, and I installed it. Sound still isn't working.
This is an exact image of the chip i bought.

lm377n_2.jpg


I put the dot towards the U on the silkscreen. Is it possible I got a faulty chip? Becuase none of my pins are bridging, and I have continuity through all the pins.

Thanks in advance,

-Cody

EDIT: If it matters, I'm getting around 1.5VDC coming off of the 330uF Capacitor, leading into the LM377N. I'm not sure if that's low or not...
 
Last edited:
For pac sound problems I start at the cd4066 and probe it with the logic probe. If the sound section is working correctly you will hear the sounds through the logic probe. If you dont have sound there the first suspect is 1M and 3M sound proms or sockets.
You can pull those and reseat them to see if it helps. I would also check the 330uf and 2200 uf caps.
 
Thanks for the insight guys! I'll check those chips when I get a chance. I'm oblivious as to what input voltage should be at the chip. What is it? 5V? Because I'm not getting that hah.
 
Have downloaded or bought the manuals w/ schematics for the game?
 
Yeah, I didn't have time to check the manual last night! I guess that would help haha.

EDIT: Just checked through the manual, didn't have any info about what voltage the audio amp needed..hmm.
 
Last edited:
You should see around 16vdc on pin 14 of the amp. If you need a datasheet look up LM1877, its the same and more common part.
 
For pac sound problems I start at the cd4066 and probe it with the logic probe. If the sound section is working correctly you will hear the sounds through the logic probe. If you dont have sound there the first suspect is 1M and 3M sound proms or sockets.
You can pull those and reseat them to see if it helps. I would also check the 330uf and 2200 uf caps.

Hey, what type of logic probe do you use or recommend?
 
Okay, I've checked the voltage coming in to the chip, and I'm getting around 3.3VDC...so what would be causing that? Just to make sure I've got this right, I've soldered the chip correctly right?(I've attached a photo of my board.

If I do have it soldered correctly, then I'm getting a low voltage at the chip. Would could it be? I just replaced basically everything in the Power supply section of the board...

Thanks guys,

-Cody
 

Attachments

  • photo (11).jpg
    photo (11).jpg
    93 KB · Views: 26
Okay, I've checked the voltage coming in to the chip, and I'm getting around 3.3VDC...so what would be causing that? Just to make sure I've got this right, I've soldered the chip correctly right?(I've attached a photo of my board.

If I do have it soldered correctly, then I'm getting a low voltage at the chip. Would could it be? I just replaced basically everything in the Power supply section of the board...

Thanks guys,

-Cody

That looks kind of like my solder jobs....before glasses.....

Check the pins, closely for shorts and solder bridges. Looks like pins 1 and 2 might be shorted with some kind of solder splash. Also there could be a short on the top of the board (under the chip) and it is hard to see but the meter will find it in short order.
 
So I'm pretty sure I figured it out, i followed the schematics, and it says that the 78GUIC is what produces the 16VDC needed to power the amp. Anybody know where I can find one?


-Cody
 
First check the four fuses and fuse holders in the bottom of the cab. Check diodes D3 & D4. The 78GU1C is part of the 5v circuit. If you look at the schematic you will see the +16vdc comes off D3 & D4. I would bet you either have a blown fuse, bad fuse holder or burnt edge connector causing your problem.
 
The 78guic chip is the voltage reference for the 5v rail. Its got nothing to do with the audio amp voltage. C29 is a 2200u cap and your audio supply voltage (+16v) is on the positive side of that. I'm betting, providing your recto diodes are good, that you have a fuse/holder problem. Be sure the wiring is intact and in good shape too.
 
Okay, well Let me start by saying I know for a fact all the fuses/holders are fine. They are all brand new, and have perfect continuity. The edge connector is fine, and has good continuity as well. Diodes 3 and 4 were bad, and now I am finally getting 16VDC at pin 14 of the LM377N. But still, no sound. The sound pot is good, however nothing happens as for sound. I'm assuming 1) In my attempts to get the sound working, I burned out the LM377N, or 2) The LM377N I received was bad to begin with. Either way I ordered an LM1877 from TW arcade. Everything else is good at this point, so I don't know what else could be wrong.
 
Back
Top Bottom