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

Matt,

You might consider checking your voltages with the chip removed.
You will at least be able to see if something else is holding down your V+,
or if there is something wrong with the supply itself.

I've found shorted tantalum caps across the V+ supply before, but it's
always resulted in blowing the fuse in the bottom of the cabinet.

You haven't really said how you determined the ics are bad.
Shorted pins? IIRC, 6 or 8 of the pins are supposed to be shorted (gnd/heat sink).

Let us know what you find.

-Mark

----- Original Message -----
From: Matt Rossiter <rossiter@ni.net>
To: <rasterlist@synthcom.com>
Sent: Wednesday, December 11, 2002 10:02 PM
Subject: RASTER: 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