MB-6582 - Noise / Distortion only when changing notes

[bsilverberg]

Hello! I just finished the base pcb (v2) using Option A power source. It's stuffed with 8 8580's and 4 cores. Voltages look good. Test tones all work. I hooked up a simple keyboard controller (using MIDI OX as passthrough) and tested each set of SID's by selecting MIDI Channels 1-4 and playing a few notes. Everything checks out EXCEPT in the top octave of notes (rightmost side of the keyboard going down about an ocatve or so, maybe a little more) there is noise or distortion (like a momentary electronic burp) when a new note is triggered. The noise isn't present when hitting notes in the middle and low range of the keyboard and it's ONLY triggered on note changes. If I play the same note over and over it's fine.

Now here's the kicker - It ONLY happens on my chips labeled CSG8580R5 (all from different years/batches). But is DOESN'T happen on the two chips labeled MOS8580R5. Anyone have any ideas what's going on and what I can do? Is this maybe related to the caps to the left of each SID? They're set to 22nf for all. Is my testing method faulty? Is there a better way to test?

Thank you so much for any help you can provide. And, as usual, this place ROCKS!

Ben

[nILS]

To rule out everything but the SIDs, try switching a pair with the "non-faulty" ones. If the problem moves with the SIDs you at least know it's SID-related.

[bsilverberg]

You ARE a Midibox HERO! I pulled all the SIDS, mixed them up and put them back (randomly swapping two with two other spares I had) and wouldn't you know it? IT WORKED! Not really sure why, but everything now plays as it should without any noise problems!

Thank you so much! Now on to build the control surface...

Thanks,

Ben

[Wilba]

Randomly swapping SIDs is not a solution. You didn't learn where the noise was coming from, the SIDs, the PCB, the filter caps, bad solder joints, etc.

I recommend you send all your SIDs to nILS for proper testing (and disposal of faulty ones).

[bsilverberg]

Send them all out, eh? Well, I will say this about the 'swapping solution' - many of those SID had been sitting dormant for years and had built up some oxidation (or what have you) on the leads. It's possible that the mere exercise in pulling in and re-inserting was enough to "clean" the SID leads off for better contact. I know that wounds 'weak', but as long as it works, that's my story and I'm sticking to it! Seriously, if there is something more specific for me to check, please let me know. I'd hate to get to the finish line only to have to revisit this issue.

Thanks!