Odd Duo Audio Issue

[nat]

Here's a new one.

Today during a game of Rayxanber II my Duo started emitting a quiet, steady white noise static-y sound. This noise is not audible when music is playing-- there are no audio glitches or anything (I had already replaced all the caps in the audio circuit a few months ago). You can only hear the sound when the music is quiet or nonexistent-- for example, between levels, when boss fights are loading, etc. The sound is present whether I'm playing a game or not. For example, if I simply turn the system on with no game inserted the static is present even at the BIOS screen. The white noise is present over the headphones as well.

What I ruled out:

1) A/V cable. Tried two (first party NEC) A/V cables with the same result, not to mention the sound is present over the headphones too.
2) My TV. Tried multiple other systems using the same input jacks on my TV, no problems.
3) Caps. I spent 3 hours replacing every f*cking capacitor on the logic board. The noise is still there.
4) A/V port. As if hearing the sound over the headphones wasn't good enough to rule out the A/V port, I resoldered the A/V port anyway.

Uhh... I think that's about it. What else does that leave? I've never heard of such a problem. All previous accounts of "static-y audio" have to do with redbook CD audio. This sound is present whenever the system is powered on at all, regardless of whether a game is playing or not.

The next step for me is to run the logic board through the dishwasher.

[Michael Helgeson]

It does it during hu-card play also? Oddly at random times I have had this happen to me with a few hu-cards only, at random times (3 or 4 times maybe in my life) on the Coregrafx I had and the current Supergrafx. Very rare,and it occurred during game play,ect...just a  constant flow of noise that bugs the shit out of me,less during gameplay as the normal audio mostly drowned it out. After I would remove the hucard  and try a different one the audio was fine,and re-insert the original one and the issue would be there again or non existent (seemed to be determined by how long I left the hu-card out of the system).

Happened to me on Rabio Lepus,and I don't remember what else. Has not happened in forever though. Good luck figuring your problem out.

[nat]

Yeah it happens during HuCard play too, or no play at all (like I said, even on the BIOS system card screen with nothing in the console).

I will surely update this space if I figure it out.

[Platinumfungi]

Giving it the old DW bath sounds like a good course of action. That could help get rid of any weird phantom problems: dirt, grime, any possibility of loose solder rolling around making contact, things stuck to the board, etc.

The sound can be heard from the speakers and in the headphones, but not internally from within the system, correct?

You replaced all the caps, or just all the electrolytic ones? Think it could be one of those damn SMD caps? I've never heard of issues with them, but who knows...

If it was an internal noise I'd say:

- Check everything power related. I once had some CMVS issues with PSU wiring that made the system emit a quiet "whining" noise.

- Check the laser. Swap lasers with another Duo and test both for any changes. Play around with the silver pots.

[nat]

Yeah, it's a speaker noise, not a noise from the system itself.

No, I didn't replace those SMD caps. I can't imagine it would be those... I mean, no one has EVER had a problem with them, right?

[Michael Helgeson]

Not that I am aware of Nat.

[Platinumfungi]

I've never heard of anyone having issues with them, but has anyone ever looked into what they actually control?  It's been a while since I've opened a Duo, but from what I recall there were enough of them there to think about. Wouldn't it be possible that some of them relate to the audio (whether or not it's the culprit causing the problem here)? I'd love to see a SMD chart...

[nodtveidt]

Sounds strongly like interference, honestly. Either that or an overload to one of the audio circuits; that could be caused by a shorted resistor or failing voltage regulator.

[nat]

Probably nothing shorted since it started at a time when my Duo hadn't been open in months.

Anyone have any information on the voltage regulators on these things? That's a bit beyond my field of expertise.

[nat]

the problem is "fixed."

A couple of runs through the dishwasher and a long soapy soak did the logic board good.

I'm going to write this one up as a case of old crusty caps leaking electrolytics all over the board and causing random shorts. Since I replaced all the caps anyway in an attempt to correct the problem, there will be no more leakage and the problem shouldn't return at all (unless for some reason that wasn't the real issue).

[spenoza]

What kind of soap did you use? I know water won't harm unpowered electronics, but I would think that soap could damage traces.

[nat]

http://www.seventhgeneration.com/Dishwashing-Soap

[COUNT SMRIFNACK]

Way to go Nat.  Glad to hear it's fixed.  What all did you run in the dishwasher?  How far did you strip down the board?  I didn't know you could wash pcb's.

[nat]

  I didn't know you could wash pcb's.

Absolutely. It was a trick I learned when I used to repair Apple Macintosh computers of the same vintage as the Duo. They suffered from problems caused by the same batch of bad caps that were prevalent in electronics of the period (including the NEC console line). We'd replace the caps and run the logic boards through the dishwasher to remove any rogue electrolytic. PCBs undergo a "bath" very similar to a dishwasher cycle as part of the manufacturing process, actually.

Way to go Nat.  Glad to hear it's fixed.  What all did you run in the dishwasher?  How far did you strip down the board? 

I ran the logic board itself. Which is to say, the only circuit board inside the Duo. It's unnecessary to strip it down at all. Just unplug the optical assembly (you don't want to wash the laser, haha) and the power supply mains and drop the PCB on the bottom rack in the dishwasher. Run a normal cycle using a gentle detergent. Let it air dry (24 hours or longer).

Oh, and you'll want to back up your BRAM with a Ten No Koe if you ever do this. Giving it the bath wiped all my save files. Luckily I did a backup not too long ago.

[Duo_R]

Nat,

did you use dishwashing soap or dishwashing detergent? The soap says "not for use in dishwasher" on it:




Let me know, I picked up both from the store today because it is actually a good product to have if you have kids in the house.