TM-3 KIT INSTALLATION
Removing the old keybed
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:
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.