Click on the title to see the fix...

The first thing I did was download the schematics from the internet and looked them over. The simple power supply section is designed around a power transistor (2SB744A) and a 9 Volt zener diode.

I opened up the synth and located the power supply section and took a close look. It was clear that transistor Q1, the 2SB744A, was burned out. I checked all the diodes near the burned out transistor and realized that the 9 Volt zener had also been destroyed. The previous owner had obviously plugged in an over powered wall wart and blown the parts. Since I wanted to keep the poly 800 in it's original state I checked on the internet for an obsolete parts supplier and bought a couple of 2SB744A transistors at $1.40 each.

I found someone on ebay selling individual keys from a junked poly for $3 so I bought a 'D' key to replace the broken one.

After repairing the transisor, diode and broken key, I found a 9V DC wall wart adapter with the correct polarity on the connector and checked it with a multimeter. I powered up the synth and it sounded great!

The next thing I wanted to do was load the memory with the original sound patches since the ones that were still in the synth had been modified by the previous owner. Another quick search on the net and I was able to find the factory patches here: http://www.frontiernet.net/~rlsnuffy/poly800/index.html

Something called midi system exlusive messages are used to load the patches back into the synthesizer. A free tool that makes this easy is called midiox: http://www.midiox.com/

Total cost of the synth plus the fixup was about $20. The approximate value of the fixed up poly-800 mkII is $100-$200 http://www.vintagesynth.com/korg/poly800.php.

Happy Fixing! Karl Williams

Gus showing what a CAD part looks like in MasterCam.

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Simulating the toolpath before cutting the part on the milling machine.

Darin white decided to demonstrate that a part could be designed and cut using free software in less than 20 minutes. He used inkscape to design a part, exported it to .dxf and then used dxf2gcode to generate the gcode for the mill. A short time later his part was cut into a piece of foam! Kwartzlab rapid prototyping is becoming a reality.

Matt Bells shows his potentiometer controlled synthesizer circuit to the group.

Creating some very intersting sounds.