Burgertime No Music or Sound

wxforecaster

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I've got two BT boards, one working perfect, the other with perfect game play but no music or sounds other than the initial "BOOOP" power on chord tone.

Any idea on where to start searching for bad components or chips? Is there a common failure point? I do have a logic probe.
 
Check if the 6502 is working.
Check the content of the EPROM @12H
Check the RAM @10H
Check the addressing of the sound chips @12C, 11C & 10C
 
I forgot to mention this is a standard Midway board set.

Thanks Sam! I'm on it. Thanks for the leads. One time I was able to boot and got hissing static (which changed volume with the pot). The other times, I get silence.

For sure the readouts on 9F & 10F (8910s) and 12F (6502) don't match those of the working boardset. The board looks spanking new with zero signs of wear or cut traces under a magnifier.
 
OK,

So here's what I found. The most obvious problem was the RAM at 10H. On the good board, I've got pulsing activity on all the pins except the VCC/Gnd. On the bad board, I have no signals on all but a few stuck pins.

However, I wasn't sure if the RAM is bad or if it's just not getting signal from the 6502 chip. I'm having trouble understanding how the sound data bus flows on the schematic.

Since it was socketed already, I decided to swap the known good 6502 chip with the one from the bad board. The bad board continued to fail, but oddly enough the good board did not produce sound either.

I can produce the pinouts that I got for both boards on chips 8C through 12C, 10H, 9F, 10F and 12F if that would be helpful. The EPROM checked out good.

I'm thinking I need BOTH a RAM chip and a 6502 at this point? If so, where can I source them both?
 
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Anyone? Am I on the right track? How do you know which is the "source" chip of dead pins that's cascading to other chips?

If I do need the 6502 sound chip and 4118 RAM, where can I acquire them? Are twistywrist/riptor both on here? websites?
 
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