I downloaded the Arris/Motorola Surfboard 6141 manual and will look at what it thinks is going on when I get a chance. With any luck, there will be some useful signal level numbers...
The Surfboard 1500 made the readings available but Comcast reprograms it as soon as it connects to the cable. From that point on, bye-bye readings. (SNMP to the cable side is blocked out as well.)
The log started working around 4:30 PM today - before that the date is Jan 1, 1970. There was a big line of thunderstorms that came through this afternoon...
Everything seems normal and accessible in the modem - it says I've got 0 to -1 dBmV down, 57 dBmV up.
I assume the next time it crashes, I won't be able to access any sensible information...
We'll see. At least I can try to look at some numbers now!