Fw: Help Needed: Midway Space Invaders w/ no sound

I'm not sure if my first post went through. Sorry if this gets posted
twice....
Can someone give me some ideas?

*******************************************

I've been working on a Midway Space Invaders and need help getting the sound
back. Normally I find this to be a fairly easy fix but I'm running into
some difficulty here. When reading the audio voltage, I'm only getting
about 6.5 volts when it's supposed to be around 18v unregulated. Last night
I noticed that some of the pins on the audio amp were shorted together, so I
replaced it with a brand new LM1877N audio chip. The chip was ruined and
some of the pins were, again, shorted together. I believe something is
drawing in too much current and killing my poor chip.

The power supply board is known to be working, so I'm pretty sure I can
eliminate it (although I'm not so sure about the flakey wiring harness).
I'm pretty sure the problem is in the amplifier section. I pulled out the
chip and tried to find any shorts in that section and replaced a couple (but
not all) of the tantalum capacitors and the nearby LM3900 chip. After that
I ruined yet another LM1877 chip! This is the point where I have to admit
my troubleshooting technique is a little limited and I don't want to destroy
any more chips. Fortunately they're only about a buck a piece at Jameco.

Can anyone offer me some suggestions? The speaker checks out ok, by the
way. - And yes, I'm putting the amp chip in the correct way. The audio
board schematics can be found here...
http://spaceinvaders.retrogames.com/html/index.html

Thanks...

Matt

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Received on Thu Dec 12 12:17:03 2002