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Some views of the microcontroller box (export version)
The rechargeable battery on the microprocessor board is liable to leak after a number of years. Tracks in the neighbourhood turn blue and some may become open circuit in places due to chemical action.
The original rechargeable nicad battery is a Varta Mempac 3.6v 100mAh. A suitable modern replacement is a 3/V150H/2P, which is lithium, so shouldn't leak.
To repair, unplug the board, noting the various connections (take some close up photos to aid with reassembly), then remove from the processor box. Remove all socketed chips and them unsolder the dead battery (again, photo IC positions for re-insertion. Scrub all tracks vigorously tracks with meths using a stiff toothbrush, then with vinegar+water, wash in hand hot water, shake off, leave to dry for 24hrs. Make good damaged tracks where necessary with wire links and solder in new battery. Finally, clean chip pins with scouring pad before resocketing each chip a number of times to help clean the socket contacts.
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