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.

RL