Humming from Asteroids Speaker

bmarkoco

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I am working on getting an Asteroids cabinet working well. One thing I've got is a good humming noise from the speaker. Seems tied to the vector monitor chatter in that the humming pitch changes as the chatter from the vector monitor changes. I'm very new to arcade game repair, so not sure where to go.

So far, I installed a recap kit from arcadeshop, but it didn't seem to make any difference.
I tried disconnecting the power feed to the flourescent light fixture but that didn't make a difference.
I tested the 5v pin on the AR1 board, and it had 5.26 volts, which seems OK, but not sure.

I've replaced the Big Blue capacitor, as I have a good hum from the power supply, but that didn't change the power supply hum nor the speaker hum.

When I turn on the machine, there is a tiny bit of crackling from the speaker, but it doesn't last once the machine boots.

The volume knob seems to be all the way down, but it still has a good bit of loudness.

The game plays and seems to sound fine, and you don't really notice the hum while playing.

I've checked forums, but can't find any posts with the exact problem... more games seem to have the AR2 board.

What else should I be checking?
 
First, make sure you have the correct AR. Asteroids needs an AR-I-01. Sometimes people put AR-I-03's in them (which were used with Asteroids Deluxe), and they are not right, as they are designed differently, and will boost the noise more. The AR-I-01 has 1000uF caps in the lower left. The -03 has 3300uF's.

The, it could be the amplifiers on the AR itself. The TDA2002 amps can fail, and cause all sorts of noise, low volume, crackling, and other issues.

The other issue (maybe most likely in your case) is a bad LM324 amp on the game board. This is the preamp, that sends the signal to the AR to be amplified for the speakers. These can go bad, and even more common is that some of the caps around that chip like to break off (as they stick up a bit), which will cause audio issues.

So, you've got some troubleshooting to do.
 
Man, you're all over the place! Appreciate the help!

First, make sure you have the correct AR. Asteroids needs an AR-I-01. Sometimes people put AR-I-03's in them (which were used with Asteroids Deluxe), and they are not right, as they are designed differently, and will boost the noise more. The AR-I-01 has 1000uF caps in the lower left. The -03 has 3300uF's.

Looks like I have the 1000uF caps in the lower left (I replaced these myself as a troubleshooting measure). I also replaced the transistor mounted on the heat sink next to the amps. Photo attached of entire board.

The, it could be the amplifiers on the AR itself. The TDA2002 amps can fail, and cause all sorts of noise, low volume, crackling, and other issues.

I had considered replacing these, however, when I look at my board, my amps say SP500 027G ITALY. Are these the right amps on the board or am I looking at the wrong thing? I attached a close-up photo of these. I can order some of these if it's a good troubleshooting step (and if the TDA2002 is what should actually be there).

The other issue (maybe most likely in your case) is a bad LM324 amp on the game board. This is the preamp, that sends the signal to the AR to be amplified for the speakers. These can go bad, and even more common is that some of the caps around that chip like to break off (as they stick up a bit), which will cause audio issues.

I don't see any broken off caps, so I don't think that's the problem. I see 2 LM324 chips on the board, one at at L9 and another at P12. It looks like a standard 14 pin IC, not an amplifier. Am I looking at the right thing?
 

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The LM324 is a quad op-amp, and will be in a standard DIP package, so that is correct.

To really know where the hum is coming from, it would be helpful to check the audio coming off of the game PCB before going into the AR for amplification.

Depending on the game, I've had good luck with a small battery powered amplified speaker. I use it and a couple of jumper wires and tap the signal from the board. If there is no hum in that audio, then the issue is after the game PCB. If the audio is there, you either have noise on the power supply that is feeding power to the game PCB audio section, or something on the game PCB.
 
Man, you're all over the place! Appreciate the help!



Looks like I have the 1000uF caps in the lower left (I replaced these myself as a troubleshooting measure). I also replaced the transistor mounted on the heat sink next to the amps. Photo attached of entire board.



I had considered replacing these, however, when I look at my board, my amps say SP500 027G ITALY. Are these the right amps on the board or am I looking at the wrong thing? I attached a close-up photo of these. I can order some of these if it's a good troubleshooting step (and if the TDA2002 is what should actually be there).



I don't see any broken off caps, so I don't think that's the problem. I see 2 LM324 chips on the board, one at at L9 and another at P12. It looks like a standard 14 pin IC, not an amplifier. Am I looking at the right thing?


- FYI, you never need to replace caps on an AR, unless they're physically stepped on or otherwise damaged. The ones Atari used were very good, and they aren't heat or voltage stressed the way they are in monitors. I've repaired literally hundreds of AR's, and never measured a bad one. Replacing the 2N3055 bottlecap transistor on the heatsink however, is a good idea, as that's the most common thing that does fail on these.

- Yes, the Italy amps are the same thing as TDA2002, just from a different source. You can replace them with TDA2003 also, if you can find them, as they are a drop in replacement. However both are obsolete, so usually the only place you can get them is China via ebay, or maybe a smaller arcade supplier (who gets them from China).

- LM324 is an op amp, in a 14-pin package. The one at P12 is the one you care about.
 
Also, another test you can do is power the game up without the game board installed. (This is safe to do.) If you still hear the hum, it's the AR, not the game board. (Though you could also have both contributing to the issue, i.e., two separate issues.)
 
Depending on the game, I've had good luck with a small battery powered amplified speaker. I use it and a couple of jumper wires and tap the signal from the board.

Good idea. I'll have to see if I have a small speaker sitting around I could do this with. Would I tap into the "AUD1" jumper connector on the PCB and the GND as well for the negative wire?
 
FYI, you never need to replace caps on an AR, unless they're physically stepped on or otherwise damaged.

Well, it didn't hurt anything I guess. :)

Yes, the Italy amps are the same thing as TDA2002, just from a different source. You can replace them with TDA2003 also, if you can find them, as they are a drop in replacement.

So I can replace the Italy amps with a TDA2002 or TDA2003, whichever I can find easily and either will be drop-in?
 
Also, another test you can do is power the game up without the game board installed. (This is safe to do.) If you still hear the hum, it's the AR, not the game board. (Though you could also have both contributing to the issue, i.e., two separate issues.)

I did this. I still got the crackling on startup (seems to stop once marquee tube is on), and a slight hum, but not as loud as when the PCB was connected. The hum seems to be related to the monitor somehow, as the frequency is similar to the Vector monitor chatter.

Seems worth starting with the AR amps and see if that helps since it's reasonably simple to do once I have the amps in hand.
 
LM324 is an op amp, in a 14-pin package. The one at P12 is the one you care about.

When buying a replacement LM324, do I need to pay attention to the letters after that? For example, I see LM324N, LM324AN, LM324DR, LM324DT, etc.
 
FWIW (and keeping in mind I'm am no expert by any means :)), some years back my Asteroids also had a pretty bad hum going on...it got to the point where it was so bad you really couldn't play the game! I had rebuilt the A/R board, added in a new "Big Blue", and also rebuilt the monitor with no luck.

Then I concentrated on the edge connector thinking it might be a grounding connection issue, but any repairs I did on the connector again did nothing to improve things. I had an extra working board set that made no difference so I knew it wasn't a board problem either.

So I finally flipped over the power brick and cleaned up/rejiggered the connections to the bridge rectifier (I think I may have added some solder even, although I'm not sure on that now), and that seemed to do the trick...the hum has been gone ever since.

Again, just FYI from my experience...

Jon
 
The LM324 is a quad op-amp, and will be in a standard DIP package, so that is correct.

Do you know if the LM324AN will work to replace that chip? I'm not an electrical engineer so I don't understand the difference bwtween an LM324, LM324N, and an LM324AN (the latter which I can get from Great Plains Electronics).

Thanks for your help!
 
Do you know if the LM324AN will work to replace that chip? I'm not an electrical engineer so I don't understand the difference bwtween an LM324, LM324N, and an LM324AN (the latter which I can get from Great Plains Electronics).

Thanks for your help!



Any will work. Get the ones from GPE and you'll be good.
 
You could have an issue in the wiring loom. These looms are now getting on for 40 years old, sometimes a small bit of resistance can build up and that can lead to humming. I had the exact same issue you describe in an Asteroids Deluxe and fixed it by repining the connector pins and crucially adding some jumper wires from the AR board to the PCB using the test points on both. I did GND and 5V but you could test it just with GND. This got rid of the hum completely for me.
 
So I finally flipped over the power brick and cleaned up/rejiggered the connections to the bridge rectifier (I think I may have added some solder even, although I'm not sure on that now), and that seemed to do the trick...the hum has been gone ever since.
So my power supply does not have a bridge rectifier. I think it has a couple of diodes instead. I guess I could check the solder joints on the small board under big blue unless you have any better ideas?
 
Yes, the Italy amps are the same thing as TDA2002, just from a different source.
I replaced the two amps with the TDA2002 amp, but no noticeable change.

LM324 is an op amp, in a 14-pin package. The one at P12 is the one you care about.
I also replaced the LM324 with a socket and a new amp, and still, no real change.

The hum I'm getting seems more connectd to the chatter from the Vector monitor. When the pictures change on the screen (and the chatter pitch changes on the monitor), it changes the pitch of the hum from the speaker.

I've also got a slight hum from the power supply, which I'm not sure is normal.

Unless there are any other ideas out there, I can live with it, I was just hoping it would be an easier fix.
 
The thing with two diodes is the rectifier. It's just a half-wave rectifier, instead of the full-wave one on other non-Asteroids bricks, which is a separate black square part.

Are you still getting the hum if you unplug the game board?

There is some chatter heard through the speakers, but it's normally pretty low. Not enough to be annoying, but you can hear it.

I'd check to make sure no caps or other parts are broken or missing on the game board, especially around where the LM324 is, in that overall corner of the PCB. There are several caps that like to break off in that area, as they stick up pretty far. Or any other cracked resistor or cap could cause noise.
 
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