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Old 5th Jun 2021, 20:45
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Join Date: Apr 2009
Location: Phoenix, AZ
Posts: 82
IFR NAV-750 and 401L To/From

I recently used my NAV 401L and NAV 750 test sets to diagnose and repair a couple of KX-170B and a couple of KI 201C Nav Indicators. I had previously only used these test sets for on aircraft equipment testing.

On aircraft both test sets give correct To/From flag sense. However, when the Nav indicator is driven directly by the composite modulation output (rather than using the modulated RF output and an intermediate receiver) the To/From flag sense is reversed. I didn't realize this when I worked on the first KI 201C and spent a lot of time looking for a non existent fault.

This sense reversal is not mentioned in the manuals for the IFR 750 or the NAV 401L. Does anyone familiar with these test sets know where this To/From flag reversal is documented?
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