Help to repair an HP91

[Paul Berger (Canada)]

The segment or anode drives are reputed to be a 1858,0044,MPQ3904 Quad NPN transistor array in pinch you could replace with discrete transistors. The cathode driver however appears to be a custom chip, but would be the same as used in a 97, in fact when I repaired a 91 it seemed the display circuit was identical.