Hey guys..
Need some second opinions on my audio board.

Here's a video (just audio) of the board, game's in test mode, and I'm cycling through tests -

Note that only SOME audio seems to be affected - namely music. The digital voices seem fine.
However, what you're hearing is at Volume 1. Changing the volume does not seem to affect.. well, anything.

I have a feeling that the EE POT (X9503) is gone because of the volume. The static could be because the POT is stuck at full volume and causing the amp (LM1875) to clip.

Thoughts?
--Mike

Thanks guys -
Forgot to mention that yes, all socketed chips and cabled have been reset. (The X9503 NOT being one of them, of course. D'oh.)

I'll check the potentiometer idea. I don't have one handy, but since the X9503 ranges between 40ohm and 50Kohm, I'll throw a few resistors together and see if that helps. I'll post later tonight or tomorrow (depending on when I get home tonight..)

If it doesn't seem to help, I'll take a look at that cap, too. I *DO* have a replacement X9503 handy, but would need to rip the old one out, and don't wanna do that until I'm more positive that's the issue.

Thanks guys -
Me.

Ah, good point, since it's on the side of W9 as the pot. Good point - I'll try the cap first.

Update!

Okay, both tests were negative, which means that the digital POT is fine.(2)

What I tested -
First I removed C18 and plugged it into the game. No change in behavior.
Then I replaced C18 and removed W9, and connected up a ~2k resistor between the pot connector. This resulted in the volume being quieter, but had the same issue - music and sound effects crackly, voices fine.

This tells me that -
(1) The crackling, on only 2 of the 3 channels, is upstream of the EPOT.
(2) The EPOT may still be bad, since I cannot adjust the volume at all. But until I get (1) fixed, I can't be sure.

Since it's up-stream, my guess is that -
(1) The Yamaha chip and sound output circuits are fine - since the tune of the music is fine, it's only the "cymbol"/"drum" waveforms.
(2) It's lilkely not the CVSD circuit either, since voices alone sound perfectly fine.
(3) Which leaves.. something on the DAC circuit.

Thoughts of what to check?

Since the music isn't affected, I don't think this will change - HOWEVER, while I don't have another game to rip the chips from, I *do* have a couple spare chips I can plug in, and see.

Thanks!
-Mike

Ah - that may be where I'm wrong then - I thought that the DAC did the sound effects, CVSD was the voices, and CH1/CH2 was the music. That's not correct?

I'll try it with another chip in the morning, and post results here.

Okay - thanks for this then. This helps narrow it down. It still seems to be on two channels (strangely enough) then.

I also wasn't clear - I don't think the static/clipping is coming from the volume, as when I had the EPOT disconnected and resistors in place over the manual pot connection header, everything sounded the same - albeit quieter of course because of the added resistance. (All channels that had scratches/clipping still had them..)

TZ's sound tests are in a slightly different order - Music, Speech, and then Sounds. I recorded another video (again, sound only). In this video, BOTH Yamaha chips are replaced with known good ones, the EPOT is cut out, and the volume is set using an external resistor at about the games 'Level 8', for comparison.

What's interesting to hear is that some sound effects (Piano Award) are entirely through the music channels, while others (like the Clock Chimes) are through the channel that's 'broken' so much that you can't even recognize it.

So, to cap (because I ramble)..
New Yamaha chips don't help.
CVSD circuit is fine, due to voices being crystal clear.
DAC channel *may* be affected? I'm unclear which sounds are being done by the YM chip, and which by the AD (analog devices) chip.

Unfortunately the CH1/2 and DAC channels share nothing in common until all 4 channels are merged together. (U7 handles DAC & CVSD, while U8 handles CH1 & CH2.) That being the case, it's possible that DAC channel is fine as well, I just can't tell because one of the other channels is sick.

Addendum - Because I was asked in PM - the reason I don't send this out to be rebuilt by someone is simple -
First, the board's been worked on before, and Second, I enjoy debugging crap like this.

Good to know!

I haven't been able to revisit this board in a month or so due to guests over this spring and house projects. I plan on returning to this board sometime in May.

Had a small scare -
Last weekend was the first time I plugged my game back in after testing the previous board. The original good board was in place. Turn game on, and audio is scratchy, like the bad board!

..Well, KIND of like the bad board.
Same issue, but WITH volume control.

This confuses the hell out of me, so I start going through the steps. I didn't do anything out of the ordinary. Except..

I exchange the Yamaha chips again. I had switched them originally at the beginning of my testing, so decided to switch them back. Appareny the YM3012 IC was bad. After putting that one back in, the board was fine.

Here's the logically confusing (to me) parts, though -
I'm 75% sure that while testing the bad board, I plugged the good board in, and didn't have any problems with it. (After doing the chip swap.)
I'm MORE sure that the bad board was still giving me the crackles with it having the 'good' chip in.

So, in either case, I'm going to be ordering a new YM3012 and Vol IC at least, and drop them in, then go from there.

Thanks guys -
Mike