Asteroids Audio Fix

[yorkshire_spam]

I've been soak testing my Asteroids machine and when it's been on a while I've noticed that the audio isn't right.
You can still hear the game sounds, but the background "buzz" on the speakers is louder than the sounds themselves.

I stuck the 'scope on Speaker 1 and Speaker 2 test points on the AR PCB - sure enough Speaker 1 shows a nice clean "audio" looking trace, but speaker 2 is just "noise"

I hooked the 'scope up to the Audio1 test points and pin 14 of the LM324 at P11/P12 (depending on PCB revision) - harder to see this time because of the signal levels, but both traces look "ok"

So the conclusion is that the "Speaker 2" circuit on the AR is faulty.

I pulled the AR board, removed the transistor at Q6, that tested fine so I put it back.

Next I removed the TDA2002 Q7 - I don't really have a way to test this so I replaced it with a NOS one and put the PCB back in the cabinet.

Everything seems ok! Audio fixed.

I only have a limited number of parts like the TDA2002 so I don't like shot-gun'ing PCBs and using them up.

Cheers, Sam

 

[bonehead]

Nice write up. I also have bad hum on the speakers on my asteroids. I will try swopping the ar1 with a another to see if the hum goes away.

Thanks for the write up.