Had a similar issue recently with my Matrix 1000, same problem - no MIDI reception (no 'dot' illuminating on the display when notes sent to unit). Turned out to be the same problem as Fran, PC900 not passing MIDI messages.
I was able to source exact replacement parts, but it's good to know the H11L1 is an acceptable replacement as the Sharp part is obsolete & getting difficult (& expensive) to locate.
Gerry