Missile Command constant hum from speakers

blkdog7

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I am getting a constant hum from the speakers on my missile command. It's not the end of the world but it is annoying. Almost sounds like a fluorescent light fixture hum. It's just CONSTANT and a little maddening. It hums during attract and during gameplay.

Things I have done:

- Rebuilt AR
- Checked voltages, they good
- Replaced Big Blue
- Cleaned connectors - edge connector looks very good and is snug. Just a visual inspection but to me it seems aight.
- Replaced ground plug on cord
- Unplugged light fixture, still get hum
- Unplugged monitor, still get hum
- Cleaned volume pot.

Do you think it's possible the big blue I got from Bob Roberts is not good? Or, anything else I should be looking at?

Also, I had another PCB and it was also humming. So, it seems to be in the cabinet and is not PCB related.
 
Could be a bad TDA 2002 amp. Those are not included in Bob's kit. I've also heard a bad diode on the ARII that can cause a hum.

Brian
 
Could be a bad TDA 2002 amp. Those are not included in Bob's kit. I've also heard a bad diode on the ARII that can cause a hum.

Brian

I replaced all of the three legged transistors that are on the heat sync. Is one of these the TDA 2002? I also replaced the round silver thing with 8 legs. I see nothing labeled TDA2002.

Are the TDA2002s the two transistors mounted to the heatsink that say 8444/8005N and with 5 legs? I did not replace these two. Looking at those I notice that one of them has a heat sync tab on the top that looks discolored from heat. Is that the part you mean?
 
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I ordered the 2002s on eBay. They were cheap. I did some more research, I have a hunch you're right. One of them looks burnt on the top.

Arc, I'll try my centipede AR if these don't work. Already ordered.

Thanks!!!!!!
 
Replaced the TDAs tonight. All fixed. And, the game is waaaay louder. I had to turn the volume down. Thanks.m
 
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