Distorted Audio in Asteroids

joetechbob

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My Asteroids cocktail has audio, but it's distorted--especially when there are multiple sounds playing. It does clear up a bit when only the high frequency sound for the smaller saucer is played (after it's destroyed your ship):

http://s1172.photobucket.com/albums...tion=view&current=AsteroidsDistortedAudio.mp4

Bad audio amps? The audio from this game board sounds great when I hook it up through the A/R board from my Asteroids upright.
 
Hmmm I was going to say that's not distortion (=bad amp) but sounds more like faulty oscillation (=bad timer chip, resistor or cap). But if it works 100% using a different A/R board, then I'd suspect the A/R board. What does the PCB from the upright do when it's in the cocktail?
 
I'll give that a try...It seems almost like sound is being modulated by the lower frequency "thumpa thumpa thumpa" noise Asteroids makes.
 
My Asteroids cocktail has audio, but it's distorted--especially when there are multiple sounds playing. It does clear up a bit when only the high frequency sound for the smaller saucer is played (after it's destroyed your ship):

http://s1172.photobucket.com/albums...tion=view&current=AsteroidsDistortedAudio.mp4

Bad audio amps? The audio from this game board sounds great when I hook it up through the A/R board from my Asteroids upright.

I tried swapping boards around again and the problem seems to follow the A/R board from the cocktail.
 
I tried swapping boards around again and the problem seems to follow the A/R board from the cocktail.

Aha! So it's the A/R board. Is it the proper A/R board (half sized) or perhaps an A/R I or A/R II from a Deluxe or Battlezone? If they are the same, just check for different components in the one that isn't working right. If they look the same, then you'll need to test the components with a multimeter and see where the bad A/R board starts to differ from the good one.

Audio portion of the A/R board is on sheet 1 side A of the Asteroids schematic package.
 
It's an A/R afaik...It didn't look like anything had been modified on it. Are A/R I boards always long like A/R II boards?

Was crossing my fingers that someone else had hit this...Thinking it may be difficult/tedious to pinpoint without an oscope.

The good news is that I have multiple A/R boards to compare against :)
 
I'd just recap the audio amp section of the A/R board myself, those 35 year old caps are probably pissed you're still running voltage through them :)
 
What the hell IC is this?

So, instead of seeing two TDA2002's like on all other A/R *'s I have laying around (something like 7), my "bad" A/R board has the following two ICs:

IMG_1560.jpg


I couldn't find a data sheet (or any other info) on this IC...Did Atari randomly use some other manufacturer or has someone attempted to substitute the wrong part?
 
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Success!

My shiny new TDA2003's came in from digikey today. I popped one into the A/R board and tested it--sounded a little better (less distorted lows). Popped in the second one and--boom! Sounds *perfect* now!

Long story short: If your A/R amplified audio is working but sounds distorted--without hum (see video)--and especially has these odd-ball audio amps (8444s) then you should probably pick up some TDA2003s. Also, one other symptom I noticed without the game board connected was that there was a sort of "ticking" sound (read: oscillation) coming from the A/R board. That appears to be gone with the new audio amps.

Here is the flavor of TDA2003 that I picked up: http://www.digikey.com/scripts/DkSe...ng=en&keywords=497-11263-5-ND&x=0&y=0&cur=USD

P.S. When I installed the TDA2003s I installed them directly against The Heat Sink without an insulator and used metal screws to secure them (as others had suggested) instead of nylon screws--this hopefully will provide better thermal conductivity and therefore a longer life.
 
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