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

Ok, I pulled out the chip and measured the voltages. The one I'm concerned
with the most is the audio voltage which was reading around 40 volts now!
No wonder it was blowing away chips. I did measure 6.5 volts at one time
(probably had something to do with pin 14 being shorted to ground), but
right now it's pretty high. I can hear the coin slot counter going nuts
too.

I double checked all the pins where the chips goes to make sure nothing is
shorted. I'm stumped. No fuses are blowing either. Help!

Matt

----- Original Message -----
From: "Mark Shostak (DOS)" <shostak@augustmail.com>
To: <rasterlist@synthcom.com>
Sent: Wednesday, December 11, 2002 8:44 PM
Subject: Re: RASTER: 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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> >
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Received on Thu Dec 12 12:17:03 2002