Are you sure you don't have random IR floating in the room (e.g. compact flouresent bulbs). Is the whole system powering down or just 861? If everything is powering down it could be any meridian component in the system that is faulty.
George, only the 861 is turning off(to standby).
The sequence is like power off/on,
means that all lights are on and the standard text on the display-but it will stay in that status for maybe 30 seconds more or less-its not a constant time.
There is also no reaction via the MSR or front panel to the 861 on that status.
Then the unit switch off, the other equipment(800,DSP) are still on.
Also very often the displays shows an incomplete text like "Mer " or "Meridian 8 "
When the unit turn off, you can turn it on again (at that time),
then it will work for a certain time-some minutes to maybe one hour.