While running a fairly lengthy series of trials, the HP34970A logger started to flash it's front panal display and issue beeps, much as it does(but only once) when power is first applied. It wouldn't turn off from the front panel. Recycling from the line cord got the same behavior.
Disengaging the interconnecting cartridges/harness from the unit got it behaving normally, so that's something to look at, but the big problem is that the 34970A will no longer communicate over the serial port with similar cartridges present, unconnected to the test harness. One thing odd is an error message occurring at power on - error 913 'module reported nonvolatile memory fault'. This error is not reported when the self-test sequence is run. It occurs only when a 34907 multi-function module, used during the initial testing fault, is installed in any slot at turn on. I'm working on com issues without this module installed. The health of that module is just one more thing to look at.
The 34970A seems perfectly normal otherwise, programming and functioning from the front panel. The issue is getting serial communications re-established. I'm using fresh, known good USB-serial adaptors on the PC, of the same type used during previous long and successful communication history, and proven null modem harnessing with the same provenance.
Lack of communication is evidenced by failure to respond to IDN query, using Visa software interface from either Agilent (secondary) or Tektronix (primary). Benchlink datalogger sofware generally links through the secondary Visa without an issue, but the same IDN query can be generated using other software.
I've scoped the MC145407 interface, and it seems completely healthy, with all voltages normal and all input signals correctly processed, but there's nothing coming back from the PC16550 for a response.
All internal supply voltages are present and accounted for, with no physical signs of overloading or damage, so far. Agilent forums are silent on the issue, so far, but I don't think many hardware guys bother monitoring things there.