[Amps] help diagnosing a bad 8450a probe ?

[Peter Chadwick]

>From memory, the original diodes are matched to a 5mV forward drop at 1mA. You can get some funny results if they aren't matched, as you get some of the switching signal coming through - from memory. teh effects will be at maximum sensitivity.
As Steve says, getting diodes from the same batch will probably do it. It's just that matched diodes come from about the same place on the wafer: it is not uncommon to get a variation across a wafer, although it's probably more apparent with the 12 inch wafers used these days for CMOS. This semiconductor processing stuff is far more of a black art than the manufacturers would have you believe - you have to have the right person spit in the mixture!
Not that  27 years working in the semiconductor business has made me cynical - and no comments from GM3SEK on that!

73
Peter G3RZP