RE: Midway Space Invaders sound problems

From: Alex Yeckley <ayeckley_at_elektronforge.com>
Date: Mon Oct 25 2004 - 09:10:43 EDT

>After doing this, whenever a game is started, a high
>pitched whine is heard until the game ends.

Although your 4006 may be bad, that alone won't cause what you've described.
You've essentially got a gate "stuck open". You might try isolating which
sound channel has the problem by pulling the various summation resistors.
Hopefully you've got an oscilloscope.

>From looking at the schematics, it seems a bad 4006 might be causing
>some of these problems. Can anyone back this up? Anyone know where
>I can order some 4006's?

Yes, or possibly the 4030. I can spare a couple of 4006's - I'll try to get
a couple in the mail on Tuesday.

>Another thing I'm getting on both sound boards is a loud pop sound when
>the game first starts and each time after you are killed.

That's the sound enable line kicking in, and about 80% of them do that. I
haven't studied the other 20% to find out why those don't. You might be
able to solve the problem by adding a capacitor to ease the edge of the
enable signal (active low going into the preamp), since it's essentially
analog.

Alex

----
ayeckley@elektronforge.com
www.elektronforge.com 
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Received on Mon Oct 25 09:10:49 2004

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