RPM intermittant falsities

[lenene]

After five years plus of dependable tachometer display, and verified with a hand held optical rpm checker, my D180, v5.5 is doing the following for the last month. Low rpm is perfect. As I advance power, at about the 2100 point, the display suddenly reads double (jumps up to the 4000s) and my red light and rpm overspeed warning illuminates. Obviously the engine is not doing this. As I increase power above about 2200 rpm it starts to read correctly and stays correct up to 3000 rpm. It does this on increasing or decreasing rpm. On the ground or in the air. HELP? thanks :-?

 

[lenene]

Additional to the above, it is a Jabiru 3300 and the only change was to replace the Bing carburetor with a Rotec TBI, but nothing electrical was changed. I am assuming no connection whatever.

 

[dynonsupport]

Connection instructions:
ALTERNATOR WIRE (JABIRU)
The most common tachometer pickoff location for Jabiru 2200 and 3300 engines is one of the alternator wires. Splice a wire off one of the two white alternator wires, connect it through a 1amp fuse to the RPM Left input on the FlightDEK-D180.

What's likely happening is that the amplitude of the signal coming from the alternator, from 2100 to 2200 RPM, increases above the threshold where the FlightDEK-D180 can count RPM pulses reliably.

We've heard this a few times in Technical Support, and adding an approximately 30 Kilo Ohm (30K) resistor inline between the white wire coming from the alternator, and Pin 32 (White/Green wire) or Pin 33 (White/Blue wire) seems to smooth out the fluctuations. The 30K value isn't critical - 27K will work fine as well as 33K.

After five years plus of dependable tachometer display, and verified with a hand held optical rpm checker, my D180, v5.5 is doing the following for the last month. Low rpm is perfect. As I advance power, at about the 2100 point, the display suddenly reads double (jumps up to the 4000s) and my red light and rpm overspeed warning illuminates. Obviously the engine is not doing this. As I increase power above about 2200 rpm it starts to read correctly and stays correct up to 3000 rpm. It does this on increasing or decreasing rpm. On the ground or in the air. HELP? thanks :-?