Korg M3 Restoration
Jun 18, 2023
The beauty of my beloved Korg M3 has started to fade. It is time to do something about it.
For many years now, I have been using the 88-key version of the Korg M3 as my main Instrument. I bought my M3 in late 2010 second-hand. Since then, it wasn't always treated nicely. It was subjected to a lot of dust, dirt, and even light rain. Also, I was always too cheap to buy a proper case for it. Nevertheless, my M3 has always been a reliable partner at home and on stage.
Unfortunately, the condition of my M3 isn't the best anymore. So let's start with the restoration.
As you can see in the picture, the front of the unit is quite dirty and has some yellow spots around the most regularly used buttons. Some of the buttons don't respond properly, and the jog wheel is completely unusable at the moment.
So let's open it up.
After removing several screws from the side and the bottom of the device, the bottom is quite easily removable.
Here I'd like to point out a quite nice but somehow unique solution.
At the right-hand side of the unit, you can see the power supply, which is just a universal 12V power supply from Korg. All the internally used voltage rails are generated from the 12V supply.
After cleaning all the parts, it's time to assemble the unit again.
Some interesting technical details
For those of you who are interested in electronics, here are a couple of things I have noticed.
The Feder / Button Boards are using Cypress PSoCs
On both of the boards, a Cypress PSoC CY8C24423A was used. This is rather interesting since the PSoC (Programmable System-on-Chip) is not just a regular microcontroller.
The Cypress PSoC has freely configurable peripherals, which in some applications allows them to run a lot of its tasks in hardware with only very little or even no CPU utilization at all. I am wondering if there is a technical reason that such a device was used instead of a regular microcontroller or if it maybe was just the personal preference of the engineer who designed this.
The 8 Pad buttons use Hall-Sensors and magnets
For all of those of you who have wondered how the velocity-sensitive Pad buttons work: Here is the answer.
In the picture above, you can see the buttons from the backside. The gray squares inside those buttons are magnets. On the PCB, you can see the hall sensors. The buttons and the PCB are separated by a rubber foil. If a button gets hit, it moves closer to the hall sensor. From the change in the output voltage of the sensors, as the button moves closer, it is possible to derive its velocity.
The big IC on the board is labeled as Korg 031204 and presumably an ASIC.