Korg Poly 61/61M -1983    Weight = 24 Lbs. Number mfg.= 15,000 MRP=$995


User Manual: Manual Manor
Reset Proceedures: N/A
Operating System code: N/Asd archive 217 is old ver of 384 for IC1 (assigner) and 337 is for IC30 (programmer)
MIDI or other control protocol: Seem Manual for 61M
Software related Links: N/A
Patches or knob settings: sd archive or Koltsov.biz had them..no more?
Circuit Overview: below
Scematics/Service Manual: Florian's pdf (full service manual) or Manual Manor
Common Service Issues/Tips: below
Parts Sources: Keys knobs semiconductors misc
Uncommon chips/modules used:M5230L Voltage Regulator, 8049 CPU's, 8253 timers, uPD8255 prog. periph. interface, SSM2056 EG, LM13600 dual ota
Modifications:MIDI IN or photos of hack job :-)
General Info Links: Vintage Synth Explorer











Circuit Overview:
     A synth 'improving on' the PolySix with digital oscillators using 8253 timer chips and LM13600 ota based filter, but lacking the diverse effects section (no chorus I see as vse claims), adds joystick with dco and vcf amounts for some useful real time control. Otherwise in parameter mode you type in parameter number and up/down button edit. And it maintains the arpeggiator in similar form with polysix. Instead of 1 VCO, it's a 2 dco Typical subtractive analog architecture with memory. The Midi version is Korg's first Midi synth, though a retro for polysix was released about the same time. I had a non-M poly 61 version that has MIDI ports also.













Service Tips:
     Problems with the keyboards are common. The 'conductive impregnated rubber' key contacts tend to get 'dulled'. I and others have had some success rubbing them with acetone. This apprently can cause the surface of the rubber to break down some and peel off with abrasion and reveal a fresh surface that has conductive material exposed. This is my theory after many operations on these and many successful ventures. I have seen cases where it just won't work though. Probably carbon thins out as you get below surfaces. SO GOOD NEWS! I did a lot of research and am having produced contact disks that adhese on nicely once you clean w/acetone. So think they don't noticeably alter performance. But on these gold contacts use 1500 grit paper and swirly about 10X per contact to get rid of old material deposits I believe... Also here is the Poly-61M MIDI board checklist and troubleshooting guide (KLM-605)

     I've seen some battery spills that damage ic12, and sometimes 8255 ppi chips and destroy nearby interconnects. Anything around..best just heat gun them out and clean up/verify everything first. One ate a trace completely and required extensive cleanup with toothbrush/ baking soda solution to get the board back in best shape. All digital stuff seemed to work well from the panel but I can't get a sound out of them. Very possibly I just hadn't edited release eg...which..on another was the final fix until i put battery in. Then it died for some reason. I studed a bit and see IC1 is functioning normal. It scans notes and i hear them in the jumbled random 'patch' in the memory's jumbled bits. The buttons on the right work to light those 3 led's. But all gates are on all the time from boot...and no programmer stuff works. Pin 21,22,23 are active since they are attached to IC1's pins. Perhaps instructions are handed between cpu's that way. IRQ never moves from high on ic30 also. And it's own pin would have to reset ic38 for that to happen. Only pin 11 and clock pins show signal now!













I have some spares - $5ea

I have most chips but synthonics.de has repro boards, cpu's, i/c pins etc. Parts:
I believe you'll draw mostly blank looks from Korg on these units. I have scrap units in stock so just ask. Contact me.


An insightful post to SDIY from Karl Dalen:
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VCF:
12db LP LM13600 using a MS20 VCA with limiting diodes in resonance
feedback but before VCA also the feedback not only goes to the input
of the filter but to first cap like half way S/K and no local OTA
gain loops but one fixed over both. 

I have checked trough all other analog Korg products and this VCF
are unique to the P61.It should have a peculiar Bw hump because of
this.

VCA:
MS20 final VCA. One SSM2056 EG split use VCA and VCF.

DCO1:
It's a complete saw VCO core, a regular Op amp integrator/comparator
design. The ramp reset comparator also feeds another comparator that
sends this signal back to *both* 1/3 of DCO1 and DCO2 8253 timers gate
input, then one of the 8253 timers sends a pulse back to the integrator
NPN ramp reset transistor in the VCO!! Odd!

Could this perhaps mean that half of timers are actually used to measure
the frequency of the VCO and if wrong in realtime restart it on a per
cycle basis?! It could work if the value are compared to a predefined
LUT. Or is it just a bogus thing to distract anyone viewing the schematic?

The output of the ramp integrator are sent to a comparator to create
PW wave.

DCO2:
DCO2 are made out of 1/3 8253 driving a 4520 divider who's output's
are selected by a switches and summed by a weighted resistor net
acting like a DAC to create saw. A redundant signal goes to divider
reset to actually turn off the chip..

Apparently resolution of wave are likely dependent of octave selected
otherwise only one switch would be needed.   

VCO ramp integrator note CV are a 7bit R2R generated by the same CPU
that scan's KBD that then feed a common expo who are muxed out to
each VCO. (Polysix/Trident) 

The driver for the timer DCO's are a VC RF multi vibrator who in turn
are driven by bend and vib voltages, the CLK signal are then driven
into a prog divider to create semitone offsets for DCO2, finer detuning
presumably by 8253 timer itself.

There are no regular muxed DAC for the parameter CV's instead each
has its own DAC trough a bag of 8255 driving a even larger bag of
weighted resistor net's.

DAC for Cf of VCF are only 6 bits. However PWM, VCF, Vibrato modulations
are full resolution from the analog triangle MG.

In other words an awful sounding poly but a great, peculiar and funny
VCO/DCO design. 

Disclaimer: I might be utterly wrong in all that said here.

Thanks for your attention....G'day...

KD
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I have some spares. $5ea.

Parts: I have some parts that are the same so feel free to ask what the current stock is on a given thing. Some of the less common parts are getting quite hard to find though. THings pop up on ebay now and then.. Contact