Fluke 8000A problem: saturation at 1V

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Hello !

I got a couple of old Fluke 8000A DMM's and they are fine except
for a common fault they share: in the 2V range, they display correctly
up to approx 0.8V, above that the output becomes nonlinear and
saturates at approx 1V for 2V input. Funny thing is that all other
ranges (0.2V, 20V...) work fine.

I assume some protection device (diode?) has gotten bad - does anybody
have an idea how to repair this ?

Thanks for info !

-BK