Keypad MOD for Prophet 600

Keypad MOD
This page details the procedure of replacing the keypad switch for the Prophet 600. This is posted for informational purposes only.

Keypad MOD

One of the weak points of the Prophet 600 is the keypad. What typically happens is one of the switches will stop responding and as the problem progress more switches stop functioning. Wine Country Productions at one time offered the control panel membrane switchpad (#S-61) replacement but unfortunately the part is no longer available. With no replacement part many Prophet 600s were parted-out. Recently I purchased one of these "dead" Prophets with the intent of using it as a parts machine, but decided this was too sad a fate for an instrument that otherwise was working well. It was a simple circuit. Thus was born this Keypad MOD.

My first plan for the MOD was to lift the keypad, remove the switch membrane, glue new switches and put the keypad back on top of the switches. I found that even with 1 mm thick switches that this did not work well because when the screen for the LED display was lifted from the LEDs, the display was not sharp. The LEDs on the RECORD, TUNE, etc.,.. switches also lost their brilliance. I also wanted to make this MOD look as close to a stock Prophet and this plan did not meet this requirement well.

I would have to use a subminiature switch (for the record I used Mouser Electronics stock number 101-0010) and drill the front face panel of the Prophet. Doing it this way I would mount the switches below the face plate and would be able to keep the keypad flush. Drilling the face plate required a lot more work (all told the project took 6-8 hours, but this was working very slowly, determining how things were to be done each step and double checking everything before progressing to the next step).

1. Remove the keypad, you should now see the switch membrane. Now carefully removed the membrane.

2. On the two wood sides of the Prophet remove the upper two screws on each side, and open the synthesiszer. Remove all connections from the upper boards to the lower boards. Note connections. Unscrew and remove the upper boards from the face panel. See picture. Remove the 6 screws on the hinge and remove the faceplate.

3. Remove residue ("Goo Gone" worked well- took several applications). Attach pattern for drilling faceplate (download pattern here). Before drilling note that the "5" and the "TUNE" holes are not centred. This is due to the fact that I decided to keep the circuit board screw points. See picture. Before proceeding attach the keypad to insure that the RECORD, TUNE,.. LEDs have a clean hole to shine through.

4. Solder the leads to the switches now. After all leads are soldered install switches. Take care not to have the top of the switch extend above the faceplate, or when you put the keypad back on it will always activate the switch. Route the wiring so that it will not interfere with the LEDs (see picture).

5. Connect new switch wiring to circuit board. Install front panel and both circuit boards. I decided to make the leads longer than needed for ease of removal of the front panel circuit board in the future. Reconnect jumpers from upper boards to lower boards. Test.

I am very pleased with the final result. It looks and feels very much like a stock Prophet.