EPROM images acquired from Rohde & Schwarz ESM500A 570.5012.22 FNr. 842875/13
by John Miles, KE5FX (john@miles.io), 28-Feb-14

B20 (EPROM I):  Image acquired from 27C128-25JL, labelled "570.6954.15 B20 -02.00- Sigma A800"
B19 (EPROM II): Image acquired from M2732AF1, labelled "570.6931.15 B19 -02.00- Sigma B800"

(Latest date code on CPU assembly was Nov 1995)

Note that B19 is a 24-pin part installed in a 28-pin socket, with IC pin 12 
inserted into socket pin 14.  Socket pins 1, 2, 27, and 28 are left empty.