Elite Avant Garde Upgrade

Items like the one pictured below occasionally appear on the short list for Top eBay Chess Items by Price. Since I've never been certain what purpose they served, I always passed over them for a more familiar item.

For this current edition of 'Top eBay Chess Items', the only other item was a 1972 Fischer - Spassky Poster (March 2013), but as that post attests, I already featured it five years ago. For the record, this time around the poster sold for US $437 after six bids from five bidders.

The circuit board in the photo received even more attention than the 1972 poster. Titled 'Chess Computer v11 upgrade; Condition: New', it sold for GBP 391 (approximately US $553.27) after 12 bids from ten bidders.

What's a V11 upgrade? The description said,

For auction a v11 mainboard for use with the Fidelity Elite Avant-Garde chess computer. The system utilises a quality heatsink which affords a silent operation and runs at 50-MHz core-speed. The system contains a 75-MHz rated microprocessor and can be made to run at higher speeds by simply changing the oscillator module which is a socketed device for convenience. A manual and power-adaptor is included which is suitable for both European and American power systems.

A second photo showed the cover of a booklet that said,

V11 Elite Avant Garde Owner's Manual
Also Versions 2-5 (6114), Versions 6-10 (6117)

A similar item at Fidelity Elite Avant Garde V.11 (chesscomputeruk.com) gives an explanation of the purpose it served:-

I believe Wilfried Bucke has created around 40 upgraded “Elites” using high-end PCBs remaining after the Fidelity company was closed and sold to Mephisto. Wilfried has fitted these PCBs into Elite A/S, Elite Avant Garde or Prestige boards. They are not all 68060 Avant Gardes by any means. Each one is probably a little different from the next in terms of its origins and accessories, board used, cpu and clock speed. This individuality and the fact that only around 25 68060 v.11s have been built makes them rare by any definition

The page includes a photo showing a booklet titled 'Custom Elite Avant Garde Owner's Manual', but the rest of the cover is too blurry to read. At least I know what the circuit board was used for: to upgrade the electronics of an attractive chess computer from the end-1980s.