Assembly - TM-3 Prophet-600 Keyboard Kit

TM-3 KIT INSTALLATION

  • The kit includes: 61 key semi-weighted keyboard with cable assembly, 3 steel Mounting plates. Plastic bag with 6 pcs M4x16 hex machine screws and an allen wrench.
  • Find a good space to work, with a table and nice lighting. Put  a towel or something soft on the table to avoid scratches.
  • Static electricity is bad for electronics so avoid (wall to wall) carpets and rubber shoes.
  • Take your time, work slowly! Pro tip: Read through these instructions once before even starting!
Fatar cutouts vs caps
Fatar cutouts vs caps
Cutouts to make room for capacitors
Prophet-600 pot leg cuts
Prophet-600 pot leg cuts
Cut these pot legs
Gently bending caps to make room
Gently bending caps to make room
Gently bending caps
Prophet-600 side panel screws
Prophet-600 side panel screws
Side panel screws
Prophet-600 keyboard connector
Prophet-600 keyboard connector
The keyboard connector

Removing the old keybed

  • Place the Prophet-600 on a table. (Of course it should be completely disconnected.)
  • Put the P-600 on its "back" and loosen (don't remove) the 6 bottom screws holding the keyboard in place.
  • Put the P-600 back down in its normal position.
  • Remove the 2 top screws from both wooden sides (see pic), and open the lid.
  • Pull the 16 pin cable going from the old keyboard to the connector on the PCB in the lid (see pic).
  • Pull one side of the P-600 over the edge of the table slightly, so you can reach the screws holding the keyboard in place. Unscrew them fully. Then do the other side and the 2 screws in the middle.
  • Lift out the old keyboard and put it away. The 6 screws for the old keyboard will not be needed for the new one.
Prophet-600 Scan Matrix
Prophet-600 Scan Matrix
The problematic resistors are marked
New resistors added
New resistors added
This is where the resistors should be added

Resistor Modification (not always needed)

There is an inherent design flaw in the Prophet-600 keyboard scanning circuit. There are 8 resistors which have higher values than ideal. An electrical engineer worked with us to analyze the circuit and his conclusion was:

- That it works at all with the original keyboard is almost a "happy accident".


Due to the longer cable needed for the Fatar keybeds, these problems are magnified and can cause weird behaviours like stuck notes or a single key triggering two notes and things like that. It seems only about 1 in 10 customers so far experience any issues so there's a pretty good chance that it will be fine.


We really strive to have all keyboard kits "plug'n'play" but if you encounter these issues with your Prophet-600 after installing the kit, you need to solve it by adding a few additional resistors (included in the kit) to your Prophet-600. It is a fairly simple operation because they can be easily added from the "solder side" of the PCB in the lid. This "fixes" the original design flaw. If you have basic soldering skills it should be no problem. If not, please find someone to help you. 


You will find the correct location in the leftmost PCB in the lid of the synth, near the middle, close to where the big connector from the main board is connected. It seems adding just 6 resistors as shown in the picture (click to enlarge) solves the issues, but we have included 8 just in case.

Fatar modifications summary

Placing a modern Fatar keybed in a Prophet-600 is a tight fit. Its physical dimensions are slightly different.

We have modified the keyboard in some places to make it fit:

 

  • The top C key has a thin bit removed at the bottom.
  • 5 mounting studs are removed.
  • 6 slots have been cut in the bottom to allow for free space around some capacitors on the P600 voice board (see pic).

 

Preparing the P-600 for the new keybed

Some preparations need to be done to the P-600 as well. It does not affect the sound or functionality in any way.

 

  • Using a pair of cutting pliers, shorten the legs as much as possible on the 5 potentiometers closest to the front: Speed, Attack, Decay, Sustain and Release (see pic). 
  • On the big circuitboard in the bottom of the P600 (board 4), carefully bend the green capacitors a little to make room for the Fatar: on my unit it worked best to bend 2 one way and 1 the other way. (see pic)
Prophet-600 cable in place
Prophet-600 cable in place
Overview of cable
Prophet-600 cable connector - side view
Prophet-600 cable connector - side view
Use the holes in the "top" row
Prophet-600 cable connector - front view
Prophet-600 cable connector - front view
Use the first 16 holes, leaving 1 unused on the right side

Surgery

  • Carefully place the TM-3 keyboard in the P-600. 
  • Inspect that the notches made in the bottom of the Fatar line up with the electrolyte "can" capacitors on the voice board and that the green capacitors are not touching the Fatar.
  • If all looks good so far, pull the P-600 over the edge of the table slightly, so you can mount the 2 "outer corner" screws using the provided black hex screws and allen wrench.
  • Do another visual inspection of the caps so nothing is stuck or squeezed.
  • Again pull each side of the P600 over the table edge so you can screw in the remaining screws. As you tighten things, keep an eye on the notches made in the bottom of the Fatar, make sure there is enough space so the capacitors on the voice board don't touch it. Also test the keys, especially the top and bottom C keys so they don't get stuck on anything.
  • The keyboard should now be securely in place with all six screws. All good?
  • Connect the 34 pin IDC cable to the 16 pin connector on the PCB in the lid, as shown in the images. Note that the cable connector has 34 (2x17) holes, and the P600 connector has 16 pins, so you need to make sure that the "top" connector row is used, and that there is an unused hole on the right side.
  • Close the lid, but before final assembly give it a test run: connect power and audio, and test all the keys.
  • All ok? Ok then put the 4 black screws back in the wooden sides
  • Done!

Techsmechs Vintage Synth | Stockholm, Sweden