Nintendo Helifire I/O board sound hiss

wantdataeast

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I am working with 3 different board sets for Helifire. Board are CPU, I/O and ESS. I have cobbled together one working board set. Now I am testing the left over boards trying to build another working board set. Testing the I/O boards now, one is good, the other is giving the sound on the machine a constant hiss. I can still hear the game sounds but the hiss is constant. The sound amps and sound chip are on the ESS board. Something on the I/O boards is causing it. BTW I am using all the wire that connects between boards on the known good set up. Anyone have an idea what area of the I/O board could be giving me issue? (Also, it is my understanding that this I/O board is very similar to the one that was used on Nintentdo Sheriff, if someone has encountered a similar Issue with it)
 

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What do you mean by a "hiss", like the crashing sound or a sound is stuck? It is my understanding that on Helifire the I/O board only triggers the sound itself. The ESS board is responsible for the sounds themselves.

I would start by checking 1B, 1C, 2B, and 2C, seeing if anything is "stuck". This snippet comes from the helifire schematics found below:

1751242210088.png
 
What do you mean by a "hiss", like the crashing sound or a sound is stuck? It is my understanding that on Helifire the I/O board only triggers the sound itself. The ESS board is responsible for the sounds themselves.

I would start by checking 1B, 1C, 2B, and 2C, seeing if anything is "stuck". This snippet comes from the helifire schematics found below:

View attachment 830011
Here is a video, maybe better to be called a garbled sound:
 
Here is a video, maybe better to be called a garbled sound:
It sounds like one ot more of the sounds are always being trigger, particularly the crashing sound.
I would start by checking 1B, 1C, 2B, and 2C, seeing if anything is "stuck". (I/O board)
I think this is where I'd start if this was on my bench. These are involved with triggering the sounds.
 
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