Sunday, August 3, 2014

Kurzweil K250 with burnt out Power Supply Board

The K250 was a truly advanced instrument for its time. Stevie Wonder had a hand in designing it; and the original sticker price back in the 1980's was over 10,000 dollars... more than a brand new car.
A look at one of the four boards in the rack mount version will show you the incredible amount of circuitry and sheer number of microchips employed in making a true landmark instrument:
This particular unit came to us with a malfunctioning power supply. On it is a type of switching power supply, with several transformers, even some surface mount work mixed in... in short it seemed that the fastest point to a successful restoration would involve just replacing the power supply PCB rather than repairing it on the component level. Although I rarely replace circuit boards, the RT65-C available from JAMECO provided all the required voltages, and enough amps to power this beast. Additionally, it provides overload and thermal protection. After installing this little beauty in there and tapping the voltages to the right wires, it worked very well. I used the original screw type connector terminals mounted on a PCB, which I covered in tape to avoid any unwanted connections. I secured the replacement power supply with screws in the same place as the original, and also added a copper strap for extra security, and  a little bit of heat sinking. I tested it for several hours and it held up well. I put a bit of hot glue over the solder points on the back of the PCB, (the pcb which contains the terminals) to protect against the likely hood of the solder points breaking through the black electrical tape. Although perhaps better aesthetics could have been achieved in this mod, it is effective and secure.

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