3458A - 210 Hardware failure - CAL VALUE OUT OF RANGE: 64

[mimmus78]

My 3458A started to trow out this error when is worm.
Self test and acal all finish with ok when is cold ... but acal all trow this error when is few hours worm.

Constant 64 is "dci zero rear 10 µA" from ACAL OHMS.
I suppose this is zero point of the 10 µA range, so maybe some leakage in this part of the circuit when some component heat.
Why this constant is only for rear? I suppose for front it's implicit in some other constant in the ohm range ... or what?

My first step I think should be:

1. turn on the meter and wait few minutes
2. run acal ohm
3. check/note the value of constant 64
4. set the meter in dci 10 µA with nothing connected and monitor drift if the zero offset
5. wait a couple of hours
6. run acal ohm again (at this point I should expect the error to appear)
7. check what is value of constant 64 again to verify how much is drifted
8. valuate the data

Any suggestion?

[mimmus78]

Ummm it seems since few days it's not failing anymore ...

Can someone check what is value of cal 64?

Mine after warmup is -1.9E-09.