Asteroids hum (intermittant)

mc300baud

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ok, i don't have much hope that someone will know the answer but just in case someone does, here goes.

Asteroids board that works except for a very low-level hum that's constantly present except when the saucers appear. at that time the hum goes away, which is kinda hard to hear because the saucers make a lot of noise. when the saucer is gone, the hum instantly reappears. this is easiest to hear when the ship is destroyed while the saucer is on-screen as the saucer stops shooting and is relatively quiet for a few moments until it disappears.

i took the board over to Dick Millikan's but it's nearly impossible to hear the hum on his test rig. i could just barely make it out (and did only because i knew what i was listening for) and he couldn't hear it at all. it's very obvious in the cabinet as having the speaker installed in an enclosure helps to amplify the low-end noise, including the hum.

very frustrating as it seems i have all the other issues with this cabinet solved and it otherwise plays great.
 
I'm not much help, but I need to get back to fixing a similar problem on my astdlx.

Maybe audio range compression is helping to make the him go away when it is loud?

What happens if you bypass the volume rheostat/pot and go direct to the speaker? I have extra rheostats by the way. They are kind of special-ordery at this point. I need to replace mine soon and go from there.
 
i don't think it's that. literally the hum is there, then the saucer comes out and it goes away totally, the saucer disappears and it comes back full force.

it's something on the PCB, but i'd be totally lost as to figure out where.

i might just drag my whole cabinet over to Dick's at some point just so he can hear it in action, but he is working on other Asteroids boards right now and i can exchange this one once he's got another ready.
 
I assume it stops for either the large saucer or the small saucer? To verify it's the Saucer circuitry making the noise while not enabled, you could disconnect one side of R77. There's really not much to it, so if that's the problem, that should narrow it down pretty well.

If the noise is still there and still stops when the saucer appears... then it's a pretty strange problem.

Also, my hum problem was that the speaker wasn't hooked up correctly... it should be connected across SPKR1 and SPKR2 (pins 3 and 4) on the A/R board. That shouldn't cause an intermittent hum, but worth checking anyway.

DogP
 
i did check to make sure the speaker was connected correctly, and that i have the correct AR-1-01 in there that's been rebuilt, the big blue has been replaced, and the main PCB has been recapped.

the hum goes away when either large or small saucers are on screen.

i'll try disconnecting one side of R77 when i get a chance, which unfortunately might not be for a few days. tonight i need to get to bed.
 
that's true.

now that it looks like Brasington's multi-Asteroids kit may be available soon (and will sound best on an Asteroids board,) i may just have to keep this machine.

that, and i got all the black marks off the left side so now it looks pretty darn nice.
 
Glad to hear it's all coming together, I hope you figure out the hum issue...that would drive me nuts too. I can't wait for that Muti kit to come out, why would that sound better in Asteroids then a AD?
 
Glad to hear it's all coming together, I hope you figure out the hum issue...that would drive me nuts too. I can't wait for that Muti kit to come out, why would that sound better in Asteroids then a AD?

Asteroids has custom analog circuits for audio, and deluxe used a pokey. The multigame board that is for an Asteroids board used the original Asteroids hardware for Asteroids audio and a pokey on the daughter board for deluxe. The multigame for an asteroids board used pokey for both games, so it'll sound different for Asteroids compared to the original hardware.
 
Try reflowing the pins of the audio connector on your AR board and see if that helps. I have seen this issue come up twice and both times this was the fix.
 
just as an update i pulled up one side of R77 and the low-level hum disappeared.

of course, so did the saucer sounds.

so it's definitely something in that circuit on the board. i may not have this machine much longer so i'm not sure if i want to try to track the problem down myself, send it off for repair, or just sell it as it to someone who doesn't care or can do the repair.
 
Sounds like the timers are not being turned off completely
I would think N10 4016B or the 566 timer itself.
 
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