Problem traced to frequency controller.

While maneuvering in US water ME found not responding in Astern direction on fuel. Tried on air and ME responded both in AHD & AST direction. Checked & found the tachometer needle rotating in the reverse of the order thus cutting off the fuel. Fuel interlock device by-passed, and engine found running normally but tachometer needle reverses on the Astern order. In other words in Astern movement tachometer needle reflecting in AHD direction. Fault was traced to frequency controller. On renewing the controller ME maneuvering brought back to normal running condition.
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