Black Knight no sound

dieseldogpi

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I had sound at one point, then it just stopped working. Doesn't work in test or during the game. I checked the fuses and they are good. Messed with the volume pots to see if it was a dirty pot deal, no dice. I also hit the reset on the sound board but nothing seems to happe. With that. I do hear the speaker hum when i first turn the game on, but that's it. What can it be? Again, the sound was working, then I had pulled the drop targets out to clean and redecal. Don't see how I could have done anything. Thoughts?
 
Sound board runs its own independent CPU and ROM set, so whatever the problem is, it's isolated to the sound board. None of the wiring runs to the playfield.

If you're hearing the speaker hum at power-up, then your audio amp section is ok, as is the wiring, the rectifier and voltage regulator too. I'd start by re-seating the CPU chip and the eprom on the sound board, may just be a sketchy socket. Theoretically it could be an issue in the speech board, but they rarely fail in this way.

-Hans
 
I re-seated the cpu and rom, still the same. No sound at all, not even like it is intermittent. I checked the voltages on the board ad they are fine. I also didn't get any crackling or anything when I move the volume pot, with it turned all the way up, I do hear a constant hum, so as you said, the speaker and amp should be good. I also tried hitting the test button with the sound selector plug not connected as per pinrepair...still nothing. Is it possible the ROM blanked out? Anyway to check this with a logic probe (cheap one)?
 
I re-seated the cpu and rom, still the same. No sound at all, not even like it is intermittent. I checked the voltages on the board ad they are fine. I also didn't get any crackling or anything when I move the volume pot, with it turned all the way up, I do hear a constant hum, so as you said, the speaker and amp should be good. I also tried hitting the test button with the sound selector plug not connected as per pinrepair...still nothing. Is it possible the ROM blanked out? Anyway to check this with a logic probe (cheap one)?

Always possible the ROM went bad, but the only ways to check that for sure are either to swap in a good one or put it in a burner and verify it.

To really dig into the sound boards, you'd need the diagnostic eprom chip which will test out the ram, pia and CPU chip. There's a number of things which can kill the sound board in the way you're describing, and it's easy to just keep throwing parts until it's fixed. The MC6808 and the MC6821 are both the same chips as used in your main CPU board, so you can always swap them (Assuming they are in sockets).

There are a couple spots you can check with just a logic probe. Power it up, hit the test button, and check pins 2-9 on the PIA chip with your probe, you should see pulsing on those pins if the software is running at all. If they are all solid high, or solid low, the problem is somewhere in the CPU circuit. If they are pulsing, the problem is downstream either in the DAC, the op-amps in the speech board, or in the audio amp circuit.

You can also try pulling the speech board, installing the jumper at W1, and testing again. This will isolate it between the two boards there.

-Hans
 
So the PIA being the cpu chip on the sound board? I used the probe on this chip and got different results. Seems like 2, 3 and 4 are solid, and 5 was pulsing. Not sure what this means exactly.
 
I may have explained that badly....


The sound board has it's own CPU chip and PIA chip on there. It functions independently from the main CPU board for the game.

Which chip had the pulsing outputs, the 6821?

-Hans
 
Oh, don't worry, it wasn't explained badly, it was more my lack of knowledge that messed me up. I probed IC9 on the sound board (looking at the firepower sound board schematic) and got those readings.
 
Always possible the ROM went bad, but the only ways to check that for sure are either to swap in a good one or put it in a burner and verify it.

To really dig into the sound boards, you'd need the diagnostic eprom chip which will test out the ram, pia and CPU chip. There's a number of things which can kill the sound board in the way you're describing, and it's easy to just keep throwing parts until it's fixed. The MC6808 and the MC6821 are both the same chips as used in your main CPU board, so you can always swap them (Assuming they are in sockets).

There are a couple spots you can check with just a logic probe. Power it up, hit the test button, and check pins 2-9 on the PIA chip with your probe, you should see pulsing on those pins if the software is running at all. If they are all solid high, or solid low, the problem is somewhere in the CPU circuit. If they are pulsing, the problem is downstream either in the DAC, the op-amps in the speech board, or in the audio amp circuit.

You can also try pulling the speech board, installing the jumper at W1, and testing again. This will isolate it between the two boards there.

-Hans

I was looking back over this thread and realized I was supposed to be probing the PIA on the cpu board that is for the sound board, at IC36. I checked pins 2-9 and they were all solid, which you had said means its in the cpu circuit, what should I be checking on the cpu board

Now that I am thinking about it, I still get no sounds when I hit the test button on the sound board. Before I go any further, I need to make sure the volume pot is ok.
 
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I was looking back over this thread and realized I was supposed to be probing the PIA on the cpu board that is for the sound board, at IC36. I checked pins 2-9 and they were all solid, which you had said means its in the cpu circuit, what should I be checking on the cpu board

Now that I am thinking about it, I still get no sounds when I hit the test button on the sound board. Before I go any further, I need to make sure the volume pot is ok.

Narrows it down to the cpu chip, pia, rom, ram or their sockets most likely. Best approach is still going to be the leon test rom for that sound board.

-Hans
 
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