This Scisys Chess Champion Mark V came to me from Germany apparently in good working order. However within five minutes of switching on it began playing up and within an hour it was unusable. The LCD screen showed pieces, bits of pieces and multiple cursors all over the chessboard.

For a chess computer dating from 1981 the Mark V is a complex machine, but taking it apart is relatively easy. This photo shows the back of the Mark V, with the main PCB, on the right. The front panel with the LCD chessboard is on the left.

When I opened it up I soon spotted a loose wire going to the circuit board at the back of the LCD chessboard. The green wire in the photo, which should be next to the blue wire. The Mark V had been opened up before with the telltale signs of non-original screws, washers missing etc. Perhaps the wire joint had been strained during a previous repair.
 

A quick soldering job to reconnect the wire and the Mark V was working again as if nothing had happened.