Korg Poly 61 pitch issue consistently up 5 semitones.

[Voyager10]

Yes, any type of 47pF capacitor will work here, well enough to see whether it fixes the problem.

 

[Midphase]

Yes, any type of 47pF capacitor will work here, well enough to see whether it fixes the problem.

That was it in the end! One of the polystyrene caps crapped out. It literally took me around the entire PCB and back since I was very reluctant to desolder them since they can be so finicky to temperature and they are typically considered pretty fail proof.

Many thanks for everything to everyone involved in this thread...it's been quite a journey and I spent the better part of two weeks trying to figure it out. I should have gone with my gut instincts to begin with since the two polystyrene caps were the most suspicious looking components on the PCB...live and learn!

 

[Script]

Happy to hear the 61 is back up and running.

Thanks for posting and big thanks to Voyager10 -- he's the man

 

[Voyager10]

<blush> well thanks for all the patient measurements, hopefully the next poor soul who has a similar problem will find them useful.

 

[mjrippe]

Happy to hear the 61 is back up and running.

Thanks for posting and big thanks to Voyager10 -- he's the man

Thanks to all, I haven't owned a Poly 61 for decades, but I was along for the ride

 

[Midphase]

Soooooo....since we got all the Poly 61 experts going on here, let me tell you all about another issue:

I actually have a 2nd Poly 61 over here, this is the one that I used to verify that on the first one the 477B PCB was the cause of the fault.

Although it tunes just fine, it's pretty messy otherwise. The owner asked me to just replace the original battery before it blows up (it's already started leaking a bit). But the main issue is that at least one of the voices (possibly more than one) sounds really crazy. It's almost as if the two DCO's on the voice are completely out of tune with one another. It's also an earlier model so the voice PCB is considerably different than the one that I've been working on.

Should I start a new thread about it?

 

[Script]

Leaked cap in the keys circuitry?

Had a digi Yamaha show up here once, returned by their repair centre as irreparable. Hitting one key made it go into mayhem... Leaked cap -- diodes had survived.

 

[Midphase]

Leaked cap in the keys circuitry?

Possibly...but the PCB looks ok, and so do the caps on the voice board (can't say the same about some of the caps elsewhere).

I need to dig into it a bit more and see if I can narrow down the issue. One of the things I really like about the newer Poly 61 (not the MIDI one, just a newer revision) is that they added small LED's to each voice to identify what voice is sounding at any given time. It's great for diagnosing stuff like this because I can at least narrow it down to exactly which voices are having the issue.

 

[Script]

Caps go bad before they get incontinent (if at all). Some just dry up..
I'd recap anyway after fourty years.