i was talking to the guy that wrote this incredibly useful guide on the poly61 about this.
http://www.mik-music.org/tiki-index.php?page=Korg%20Poly-61%20Repair&pagenum=1Because DCO1 is a digitally controlled VCO theres no way to individually tune the voices but his idea was that i was just getting the raw VCO and it had lost its digital control. I was getting nothing on my scope where i was meant to be seeing the TTL signals that control the pitch for the DCO1 so i would say he was right.
I'm using the past tense here as i was just tracking down the source of the clock signals when i went to make a cup of tea, and when i came back and turned the Poly back on it was dead. Now when i turn it on all the button LED's come on at once, the numerical LED displays stay dark and it won't respond to any button or key presses.
I'm guessing this is going to be down to some crappy logic IC dying for no apparent reason but its a pain in the arse trying to track it down. Its been suggested to me that the 4051 IC's were causing the problem with the tuning in the first place. I'm certainly a little wary of these chips after rebuilding a Poly800 which had at least 5 dead 4000 series logic IC's
The battery appears to have been replaced on this poly61 some time fairly recently already. I can see that there was some very slight leakage at some point but its been cleaned up well.
> I've heard something similar -- From that guy who seriously modded his poly-61 on YouTube actually. He say DCO2 is completely digital.
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> But you can have VCOs generating a waveform, while using a D/A to control and automatically trim the voltage it receives based on a sampled frequency that is compared against a digital clock. Synthesizers like the Jupiter-8 and Sequential Max have VCOs that are digitally trimmed with a built-in auto-tune function.
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> The Poly-61 is probably similar in that respect, and I would suspect resistors and caps in the area of the A/D or divider circuit they are using to sample the VCO outputs. If these voltages are not correct, or the caps are discharging too soon, the CPU will interpret the frequency incorrectly. That's just my guess... I bet there's nothing at all wrong on the voice board.
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> Did you have to replace your battery? Did it possibly damage the main board at some point? Mine's completely hosed and it's difficult to tell which components are damaged and which only look bad. Even the traces are suspect. -pc