Discussion about the Korg PolySix synthesizer

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Could be the control voltage demultiplexers?

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On Saturday, October 12, 2013, wrote:

Can't really help out, but have you seen synthhacker's blog on how the P6 detune unisone mode? Excellent article that might add to better understanding of the topic?

http://synthhacker.blogspot.no/2013/08/polysix-disabling-built-in-detuning.html

---In PolySix@yahoogroups.com, <polysix@yahoogroups.com> wrote:

Hey guys, Have a polysix here with a voice issue. I am thinking that it may be a bad track or something similar around the key assigner circuit somewhere, but I was wondering if anyone could help with where exactly I should be looking. The symptoms are - in poly or unison modes I can only get voice 0 to sound. All the voice LEDs cycle as normal, however only voice 0 actually has output. I then found that when I pressed on the board around the key assigner/CPU area on klm366 all voices could be heard and triggered successfully. This is an intermittent connection of some sort surely, but I'm having trouble locating it. I have verified continuity along the data lines and they all seem good. The board does have some minor trace repair already, on IC3 from memory. But it has never had a battery fail issue. It seems really strange that the LEDs light, which would indicate gate signal is present (?) but then the voices don't sound. Perhaps this points towards something between the envelope and the filter? Anyway any input from you wise people would be much appreciated. I'm not familiar enough yet with the polysix circuits to know what may be happening. Thanks a lot Luke

Hey guys, I checked out synth hackers blog. Definitely helped my understanding along. Cheers. I am hoping to be able to check out the CV de multiplexers tonight. So you are referring to IC 31 for pitch CVs right? And then others for Env, gate etc? Thanks again, Luke

Hi,

Chip from synthacker here. Thanks for checking out my blog.

Your voice problem is wacky. The fact that you get all voices to work when pressing on the key assigner area is perplexing but hopeful. I mean, you've at least proven that you synth can work properly eventually!

To figure out which signals are intermittent, I would probe areas of the circuit for each voice. I don't think that the problem is in the voices, but probing there will tell you whether its the Pitch CV that's missing, the Gate that's missing (clearly,it's not the gate), the Filter CV that's missing, or one of the other signals (like PWM or something).

So, in each voice that's NOT working, I'd probe the following areas:

Pitch CV: Press and low key and measure on either side of R152. Repeat for a high note. Big change?

Filter CV: Set the env amount to have no effect. Set Keyboard Amnt to zero. Turn the filter knob open all the way. Press key. Measure on either side of R129. Repeat for the filter know closed all the way. Big change?

Gate CV: Well, the LED lights up, so it's clearly receiving the gate command

Resonance CV: Turn the resonance to zero. Measure pin two of IC32. Compare this value to the value from the voice that works. Is it similar?

PWM CV: Turn the PWM knob to zero. Measure Pin 6 of IC36. Compare this value to the value from teh voice that works. Is it similar?

Hopefully, for one of these measurements, it is clear which CV signal is not making it to your silent voices. Once you know that, you can then start tracing those signals back from the voice circuits to find where they appear. Or, you could go the other way and trace the signals from where they're generated to find out where they disappear. Either way, you'll find the trouble spot.

Chip

Hey Again,

Thanks chip for your lenghty and helpfull input. I had actually probed around the areas you mentioned but couldn't notice anything that stuck out.

Although good news is, I was a bit suss on a couple of the IC sockets, including the one which the key assigner CPU was in and tonight replaced them and reflowed a few other questionable spots. And now she's workin like a charm!! No more intermittent control signals or pushing on the PCB.

So thanks again all for your input as this issue is now solved. woop!! Just finishing tuning it up now.

On a side note, Chip I was also kind of worried about the operating temperature of my PSU. Measured at 60*C just like yours so I am guessing that is normal? The datasheets for the 4 power transistors indicate they can run up to 150*C or something so at least that is reassuring....

Cheers,

Luke

I'm glad that you got it all working. Success!

And thanks for sharing the temperature measured inside your Polysix. Gives me extra confidence that my own measurements are OK.

Enjoy your working synth!

Chip