Circuit Overview:
Korg's first ROM based waveform synth; a hybrid with 6 analog filters. Two D7811 processors used; one for the programmer, MIDI/Tape, keyscanning/buttons and display control and the other to manage the sound production. These use three potted modules that are fed CV's from 4051's and have op amp buffered outs that feed the vcf log pins. I'm not sure what these do. Anyone? A clever bit of digital domain harmonic manipulation is used to generate the 8 waveforms though to a DAC-08 and then to the NJM2069 vcf/vca chips. The sound is similar to the Kawai K3 in many ways it seems programming it. I suppose the waveform technology is pretty similar.
Service Tips:
Typical problems with contacts in the Panasonic type keyboard I suppose though the one I worked on was fine recently. I had one where a clock resonator failed. Replaced with a 12Mhz one I have a bag of here that worked swell. The pins of the D7811 were all flat line. So pretty much that or the cpu itself was the problem there probably. Amazingly though the battery measured 3.2V or thereabouts, I was losing memory on even brief power downs! C29 is an unoccupied through hole so I occuped it with a 22uF electrolytic in parallel with C30 the ceramic disk cap that was occupied on this board. That fixed the issue. Not sure why that developed... Here's a photo of the analog board, KLM-655.
Parts:
I believe you'll draw mostly blank looks from Korg on these units. I have some parts that are the same so feel free to ask what the current stock is on a given thing. VCF Chips I could scrap from a DSS-1 board, and most of the smaller digital chips of course but there are several things like the wave rom and ROHM modules that would only be available from a scrap unit I'd think. Contact
