Project Korg Polysix (Analysis)

I got my hands on some 30 year old vintage analogs. I will try to refurbish them and incorporate them in Interdictors future productions. One of them can be seen below. A Korg Polysix that seems to be produced in 1984. I am going to do a total makeover this one. I will document every step I take with this classic synth and it´s going to start today with some inspection and analysis. So here it is in all it´s glory.

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First of all I connected it and tried to browse through a few presets. I tried all buttons to find out what state it was in. The presets were sounding odd. I had a hard time to use some of the buttons and the lfo seemed to modify stuff that it wasn´t supposed to. I tried creating some patches but some leds where blinking in strange rytms and the noise level of the instrument was terrible. Some typical signs of a common Korg polysix problem, battery leakage. As you can see below two black keys were tilting and broken and the mod wheels were in pretty bad shape. The wooden sides are damaged from some touring and the arpeggio latch is totally broken. Overall it´s in pretty bad shape.

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So it was time to look inside. You  can find a very good guide of how to open the synth over at Oldcrows. In the four corners of the front panel you will find the screws that hold the front panel in place. These are the large screws. Remove these. Then it´s time to look under the synth. There are four more screws in the front end under the keyboard that should be removed. Now you can gently tip the control panel up in a “hood-up” position and start looking inside the unit.

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You can see above what it looks like inside. Located as the second board from the left is the KLM-367 board. That´s the cpu-board that more often than not has some evil battery leakage. So we start by removing this board for some further inspection. First of all we need to desolder a black ground cable that is soldered to the top left of the board. Then all connectors must be decoupled. Since the connectors are fastened with glue we need a a scalpel or some other sharp knife to crack the glue and then gently pull out the connectors from it´s sockets. Finally there are four Philips screws holding the board in place. Remove these screws. The board is now loose and can be slided upwards away from the keyboard and finally lifted up.

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So this is what it looks like.Beautiful engineering from the beginning of the eighties. Notice the large blue battery in the bottom of the picture. And to the left of the battery some of that infamous battery corrosion. This wasn´t that bad I guess. The leakage needs to be cleaned and as you can se the chip to the left of the battery a 74LS08 is affected by the corrosion so it´s best to change that. This is what I am going to do until the next time:

  • Desolder and remove the battery
  • Desolder and remove both the 74LS08
  • Put in a new battery using a socket
  • Put in 2 new 74LS08 using sockets
  • Try to read back the presets to see if this part of the refurbish procedure was successful

I will be back with some news in a day or two!

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