Hello Dick,
".. internal overload: 72" might be caused by a failure on calibration,
as '72' might refer to the 'dcv 10V gain' (see calibration manual p. 5-6).
Either an ACAL failed, caused by interrupting this process, or an
attempt to calibrate the internal 7V reference has gone wrong, also
because of interruption, or because of unstable / inappropiate external
voltage reference.
Please read out cal constant 72 by "CAL? 72", on my instrument it's
1.00435...
If you scroll the text to the rightmost, an additional string states if
the calibration constant is valid.
Then read out cal constant 2 by 'CAL? 2', that's the internal 7V
reference. Should be betw0en 7,0V and 7,5 V, acc. to LTZ1000 datasheet,
but typ. around 7,2V. It's 7,2165..V on my 3458A. Again, scroll the text
righmost, if the constant is valid.
If 7V ref constant is corrupted or out of range, a basic calibration
might help.
Btw.: Any clue about the history of your instrument?
Best regards - Frank Stellmach
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