Firmware pulled from HP 3456A S/N 2015A01515
Chips read as MC68764 date code: 1987

These chips are 8kx8 24 pin devices

HP part numbers:
U5: CN52681N 1818-1629
U7: CN52683N 1818-1630
U8: CN52684N 1818-1631

Checksums:
U5: C9CF5
U7: CD212
U8: D4CE2


Note: older instruments have six 4kx8 ROMs. 
The manual seems to infer the firmware is the same.
To switch to the 64kb devices only a jumper needs to be moved, removed or installed. See Manual

Please send any info regarding success or failure to use EPROMs with part numbers and programming info.

Thank you

Didier Juges KO4BB
didier@ko4bb.com
March 17, 2007