Is it possible to get replacement parts for a PSR 520 (preferably by mail). If so, where and how can I get them?

I am living in St Petersburg Russia, and have not been able to locate an authorized service center here. I wrote to Yamaha, but got no reply.


Description of problem: It appears that the PSR 520 keyboard needs a replacement 'keyboard decoder' board (my terminology--I don't know the term that Yamaha uses for this board, as I don't have access to any technical literature. It is the small circuit board located directly under the keyboard.). The ID numbers on the board are XR736(C) and MKS2.

Some keys play normally, the action of other keys is affected if another key is pressed at the same time, one key (middle C) does not play at all. I have cleaned and verified contact of all the key switch pads. I could find no broken connections or short circuits in the ribbon cables connecting the decoder board to the key switch boards.