Yamaha RX-17 Modifications
 
Here is a detailed description of the modification process of the Yamaha RX-17 digital rhythm programmer. This is a relatively simple drum machine from the late 1980's, yet provides a more diverse sound set than better models in the same series. The RX-17 contains all of the standard drum sounds (kick,snare,hi-hats, toms, cymbals) and also includes some latin percussion (congas, bongos, agogos, whistle, timbales, and cuicas).The RX-17 has MIDI in and out, stereo outputs, headphone outputs, and DIN cassette interface. I would compare this machine to a Roland TR-505, except that they are generally found for much cheaper. This particular unit was purchased on E-Bay for $21.00, while the TR-505 generally goes for well over $50. This is the second RX-17 that I have modified, after selling the first I realized just how useful and how much more I could get out of this machine. To begin the mods, remove the 6 screws on the metal baseplate, and remove the baseplate. This is what you will see....
There is not very much room to work with inside this machine for mounting switches, pots, etc., so I have mounted a small box (2 x 4 inches) to the side of this machine. Once inside the machine, there are three IC chips of primary importance. On the printed circuit board these are labelled IC 114, IC 115, and IC 116. These chips are color coded in this diagram as follows:

-IC 116 (printed with YM 3012 on the chip)-RED

-IC 115 (printed with XC258AO)- MAGENTA

-IC 114 (printed with XB811AO0)-BLUE
First, you should program a pattern with a beat of your liking. Hit start, let the beat play, and turn the machine over.
On IC 116, bridge pins 4 and 12 with an LED of your choice. This produces an overdrive type distortion. I added a 10K audio potentiometer in series for control, and a switch. The anode :) should be connected to pin 12. The only difficulty of installing this mod is the large heat sink right next to this chip. I had to grind away a small portion of this heat sink with my dremel tool so that I could reach it with a soldering iron. This particular IC (the yamaha YM 3012 chip) can be found in many yamaha drum machines and synths including the RX-15, RX-17, RX-21 and the FB-01 sound generator(and possibly others). This mod works in all of these machines, the LED can be replaced with a resistor, potentiometer, or capacitor of different values for slightly different effects.

On IC 115, there are many possibilities for sounds. By bridging pins of this IC together various synth tones, distortions and phasing can be obtained. Try connecting pin 27 with any of pins 6 through 10 for low to high tones. I also used pin 15 connected to pin 20 and to pin 18 with a SPDT switch. Other options exist, but these were my favorites.

On IC 114, there are also numerous sounds to be discoverd by again bridging pins of the IC together. Some to try include pin 9 to pin 30, pin 10 to 14, and pin 20 to 28.

After determining which sounds I liked best, it was time to wire it up and put it back together. I used a small project box bolted directly to the upper left hand corner of the machine for my new control center. I have included the distortion LED and pot, and 6 SPDT switches in the box. The total modification time was about 3 hours, one hour for probing around (which I just saved you), and two hours for assembly. All of these modifications function with MIDI, otherwise I don't think I'd spend so much time on them. After completing a project I like to relax with a beer or two. I recommend Schlafly summer kolsch or Shiner hefe-wiezen. (Really any beer that doesn't come out of a can or have the word "light" on it goes well.)
 Additional notes:

-I buy my parts from ALL ELECTRONICS, this project cost me less than $10 in parts.

-Always wear safety glasses when using a dremel tool, because they like to send crap flying everywhere.

-My girlfriend likes it when I wear a mask so I don't inhale too many solder fumes.
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