Older TiVos Hughes SD40's random shut off

I do hope this is not a repeat of the TiVo restarts a few years ago. My older TiVo's are just shutting off, not rebooting, just shutting off, both of them at the same time. I have to unplug them and recover. Has happened three times now in last week. Anyone else having this problem with their older TiVo's? Thanks.