Mad Planets Sound Problem ...

kentmurphy

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My Mad Planets is having audio issues again. This time it will randomly plays strange sounds during the attract mode. The sounds are usually the explosion sound and they begin when the high score table is displayed. I have run the audio self-test and everything checks out ok. Any idea where to begin on this one?

Thanks,
Kent
 
Thanks Riptor. I replaced the 74ls377 at a10 quite some time ago and thought it fixed my problem.

http://forums.arcade-museum.com/showthread.php?t=79509&highlight=mad+planets&page=2

The audio started failing again, but then magically it started working again. It wasn't until about a month ago the sound started having the problems I described in my first post. I'm confused and not sure what to do next.

Kent

If you haven't yet, try one more different 74LS377 and see if that helps. Sometimes the replacement chip can be bad. If the same problem persists, you'll have to look further upstream in the circuit. Observing the control signals to that chip with a scope while the problem occurs (when high score table is displayed) may help track the problem down.

Bill
 
Bill,

Thanks. I've used a scope before, but not in this manner. Can you give me some pointers? What would I actually be looking for or is that too in depth to cover here?

Kent
 
Basically observe the control signals going to the speech board to see if they are changing (causing sounds) when they should not. Then work backwards from the control signals following the schematic to see what is causing this when they do change.

Best,

Bill
 
Had a chance to do some more troubleshooting this problem. There is clearly something wrong with the harness carrying the +5 supply to the sound board. While it is +5 at the power supply pcb, it varies at the sound board pcb from +4 to +4.7. Unfortunately while measuring the +5 supply, I shorted pin 5 and 6 at connector P3 on the power supply pcb killing the +30 supply. I was measuring the voltages from the solder side of the pcb, my hand slipped, and the multimeter lead contacted both pins. Not sure what I killed in the +30 supply, but it should be a rather simple fix. I just hope I didn't blow the amp on the sound board. Oh well. Now I just need to find time to do this.
 
I fixed the +30 supply. D26 was open. Now I need to resolve the original issue which prompted me to start this thread. One thing at a time.

Kent
 
If you are seeing a large voltage drop at the sound PCB then use thicker wire between it and the sound PCB, or run additional runs of the thinner wire.
 
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