RX-15 Modifications:
To
open up the Yamaha RX-15, first remove the five screws holding on the
plastic rear panel. Next, turn the machine face down, and remove the
eight screws along the top and bottom. To have clear access to the
circuit board, you should disconnect the white wire harness located by
the output jacks. You should now see something like this :
We’ll
start with IC 10 on the circuit, which is a large chip with alternating
small and large pins which reads YM 2154 on top. This is the CPU of the
drum machine, and handles most of the functions. In the picture below, I
have marked 4 pins with a sharpie. If you connect pin 59(with the
solitary mark) to either of the other pins I have marked, you will get a
harsh sounding distorted synth effect to varying degrees depending on
the pin choice. It is imperative that you DO NOT experiment with the
pins on the other side of this chip or you will do PERMANENT DAMAGE to
this machine. Trust me; I’ve learned the hard way.
Next,
we’ll move on to IC 15, the YM2190 chip. I believe these are the ROM
chips which contain the sounds for this model and the RX-21 models. By
connecting pin 7 to pin 12, a decent distortion is created. Other
connections on this chip result in muting of sounds, and clicking
variations. There are not any negative consequences to experimenting
here, but not much else to be found either.
Next,
we’ll move on to IC11, the YM 3012 chip. This is the D/A converter for
this machine. By connecting pin 4 to pin 11, some digital signal is fed
into the analog output, resulting in noisy distortion. This connection
works best when filtered by a capacitor. Experiment with values, I chose
a 1.5 picofarad (102) metal film capacitor to suit my tastes.
Finally,
we will work on IC 16, labeled YM4556D. This chip is one of the output
opamps. Connect pin 3 to pin 7 for an overdrive type of distortion. I
used a 10K potentiometer for variable results.
After these mods are completed to your satisfaction, you may drill the housing for the RX-15 near the top for the switches and potentiometer. Solder all of your connections, test, and reassemble the machine. You have now made a crappy drum machine slightly less crappy, or more if you see it that way.
E Support™ On/Off Mini Miniature Toggle Switch Car Dash Dashboard SPST 2Pin Pack of 10After these mods are completed to your satisfaction, you may drill the housing for the RX-15 near the top for the switches and potentiometer. Solder all of your connections, test, and reassemble the machine. You have now made a crappy drum machine slightly less crappy, or more if you see it that way.
