Ms. Pacman - No Sound

Straximus

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Hey guys. I have a Ms. Pac-Man that sat in storage for several years. After I pulled it out and brought it to my house, the sound stopped working after about 30 minutes of play. This happened some time ago, and I've just been too busy to deal with it. Other than the lack of sound, it's continued to work fine.

There is a constant hum once the machine is powered on. The hum will change in volume if I adjust the pot. Running my finger across the pins of the lm377 amp results in static, so I think it should be good. I've cleaned and reseated the edge connector.

Any ideas? Based on what I've read I think my next step is to start replacing caps in the sound area, but I wanted to ask folks with far more experience than I have.
 
This is where an oscilloscope, logic probe with audio sounds, or an audio probe would come in handy.

If you had sound output from the resistor ladder off the 4066 then you know it's somewhere in the audio amp stage... If you didn't have audio output then you'd know it's in the digital section of the audio.

If it's in the digital section of the audio, the logic probe can be used to check the inputs and outputs of the 4066 IC. If the inputs are good and outputs are bad then replace it.

Next go backwards in the circuit and check the 74LS273 and the sound PROMs with the logic probe. Keep working backwards through the circuit until you find where the signals stop.

The 74LS273 at 2M and the PROM at 3M are ones to check immediately after the 4066 if you have no sound output from the digital section.

Now if you have really high pitched beeps/blips for sound (may be high enough in pitch that you might not hear it if you have bad hearing) then check the 74LS283 at 1K.

RJ
 
My logic probe has sound on it and I can probe the 4066 to see if the sounds are there. If I can hear them there you move to the top of the board to the amp side. Yeah, the same as what ray just said.
Judging by what he said about it humming I would lean torwards the caps first.
 
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This is where an oscilloscope, logic probe with audio sounds, or an audio probe would come in handy.

If you had sound output from the resistor ladder off the 4066 then you know it's somewhere in the audio amp stage... If you didn't have audio output then you'd know it's in the digital section of the audio.

If it's in the digital section of the audio, the logic probe can be used to check the inputs and outputs of the 4066 IC. If the inputs are good and outputs are bad then replace it.

Next go backwards in the circuit and check the 74LS273 and the sound PROMs with the logic probe. Keep working backwards through the circuit until you find where the signals stop.

The 74LS273 at 2M and the PROM at 3M are ones to check immediately after the 4066 if you have no sound output from the digital section.

Now if you have really high pitched beeps/blips for sound (may be high enough in pitch that you might not hear it if you have bad hearing) then check the 74LS283 at 1K.

RJ

Could you explain in a little more detail how to do this. Just got a logic probe and am using it for the first time. For the resistor ladder of 4066, I assume you mean R1 thru R5. What types of readings should I be getting on those? My probe has a TTL/CMOS switch, a pulse/mem switch, a red hi light, a green low light, and a lil speaker for sound.

How do I check the 4066? What does it mean exactly to keep working backwards till the signals stop?

Thanks. n00b here.
 
I dont remember exactly which pins but its somewhere between 9 and 12 of the 4066. Start a game and probe those pins. You will actually hear the game sounds through your logic probe if the signals are being generated. If you have sound there you can move up to the top of the board and start checking things in the sound amp area.
 
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