I owned an MX135 and periodically it would lock up and I was always able to resolve the issue. I would unplug the unit and while unplugged I would toggle every switch on and off. The I would turn each dial to full extreme, doing this drains all capacitance and allows the processors to return to default original settings. Once plugged back in everything worked as new. I had and MX134 and had the same results.
Good luck
Good luck