Recently, I found an HP-9810A in overall good shape. It
is quite dusty, but works OK, as far as I can tell.
However, on the top LED row (the z-line), one segment
of each LED (it's the bottom left segment) is not functioning. Since it's the same segment on each LED I
guess some driver transistor is dead.
Could anybody please point out how to repair this? Or
how to find out what really is wrong? Thank you very much.