Did some searching and reckon it might be a battery (CR2477 form an earlier post) But just in case it could be something else I'm going over symptoms here.
1 The board was turned on to find all submaster lights off and contents gone!
2 A backup disk was read in but this did not inhabit the Subs.
3 The system clock is showing correct Date, Time etc.
4 A Sub was programmed and the board turned off for just a minute or so. When it came back up that sub WAS inhabited (green light). Good news. But
5 After leaving off for 5 minutes the subs were again gone on startup.
Sooooooooooo!, No master clock problem but one of a failure to hold on to or load Sub data. (probably cues as well but didn't test them)
The bad news; this board is probably about 20 years old!
Earlier Expression 3's used two super capacitors to retain SRAM data. Newer and retrofitted Expression 3's use the CR2477 battery for SRAM data.
It sounds like this particular Expression 3 may have supercaps for the memory, instead of a battery. To check, open the console, and unscrew the five screws from the CPU tray in the middle. On the PCB edge closest to you, there will be either two nickel-sized round components next to each other, or a battery.
If it does have supercaps, they're likely failing. If it has a battery, you can check the voltage with a multimeter. As long as the voltage is above 2.2V, the SRAM will retain memory. A good battery will be about 3.0V.
If the console has a good battery, then there may be a deeper issue--possibly a failing voltage control chip or failing SRAM. If the console has supercaps, it can be retrofitted with a battery.
The good news is, we can still fix an old Expression 3, and retrofit it with a battery if it has supercaps.
Thank you. I was thinking battery (or supercaps) but what threw me was that I could not reload from a disk. The system found the disk and said it was loading but still no sub data. I'm back in the theater later today and will let you know more when I've opened the CPU tray.