Is there a frequented metal-detecting usenet group?

I've been asked to repair 2 old detectors
The 1976 "Yukon 77B" I've repaired but if anyone knows more about the 2
National Semiconductor 8 pin DIL custom? chips marked 274 0-004 and 624
0-001 I would be interested.

The 1978 "Coin Magnum" seems to be vaguely working in the opposite sense to
how i'd expect , does anyone one have normal operation guide or any
technical details before I delve in deeper , at least it uses industry
standard chippery. Anyone know what the central lump covered in vacuum
moulded cover is hiding?

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Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/