This module was part of a radar system. Inserted into the video line driving a 512 line CRT monitor, it effectively provided controllable persistence on the operators radar screen. But how do you keep an essential system running when it depends on an electronic sub-system based around an obsolete magnetic core store?

Sometimes it is cheaper to start again from scratch. We designed a form, fit, and function replacement based around an Actel A42MX series FPGA and a RAM chip. The Actel antifuse device was chosen because it operates at five volts, simplifying the design when the original equipment was built with 54 series TTL. The 54 series components were retained on any external interface pins to ensure signal drive levels, noise immunity, and thresholds exactly matched those of the original equipment.

You can click on the images above to enlarge them. Two show the old unit sitting along side its functional replacement. The third shows the contents of the new enclosure, and also demonstrates that despite the huge reduction in volume the box is still largely empty, needing only the single circuit card shown there. The excess volume in the new case is a consequence of having to make the shape and size of the enclosure compatible with the existing mechanical attachment points and ensuring the interface cable to the rest of the system would reach the Hypertac connector on top of the new enclosure without any sharp bends.