Some M50 series keyboards suffer from an issue that may cause the following symptoms:
*** Important Note *** If the display indicates "Error updating the panel" instead of "Completed", then the issue is due to a problem with one of the front panel boards, and the rest of this bulletin does not apply. Check the last panel that was being updated before the error message was displayed. It may be a simple loose connection between the main board and the panel PCB, or a problem with the key scanning chip on the panel PCB.
Any disruption of communication between the main board and the front panel boards can cause a lock-up. On some early units, component tolerances have resulted in a higher than normal ripple voltage on their 1.8 volt power rail. This ripple negatively impacts communication between the host CPU and the PSoC chips on the the panel boards, resulting in the symptoms mentioned above.
Operating system 1.0.5, and later, reduce the overall current draw of the CPU. In most cases, updating the operating system will solve the issues. If the main circuit board (KLM-2887) is revision D or lower, replacement of a couple of capacitors is also required, and is described in the procedure section below. The capacitors do not need to be changed if the board is revision E or later.
If the update and capacitor replacement do not solve the problem then there may be a physical connection issue between the main PCB and panel PCBs. Check the connection of the harnesses between the main PCB and the panel PCBs (CN1A to CN1B and CN2A to CN2B). Reseat any loose connections, resolder any questionable points, and replace the harnesses if necessary. The harnesses are part # 500475103867R and 500475103868R.
Replace capacitors C153 and C37 with a low ESR type supplied by Korg. Do not substitute any other capacitor. Please note that some versions of the PC board do not have a capacitor C153. In that case you will only need to replace C37. The part number for the Low ESR capacitor is 47UF10VLESR.Continued on next page...
The following images show the capacitor locations.
The latest operating system can be downloaded from the support area of korg.com.
Follow the instructions included in the Operating System download package. You will need a SD card to transfer the updated files to the M50.