Memory modification
The first build option for the NDH-518.
With UP/DOWN counter and home-made opto encoder control
( with older original 1984 hand-drawn version of the up/down PCB )
+ eprom BIN-BCD decoder in a 27C32 EPROM for 4 x 64 channels display.
I didn't had the GAL stuff yet.
Click on pictures to enlarge
Jump back to the NRD-515 webpage for all the hardware info