Tach not reading accurately

[Bluth125]

I am going through my condition inspection and the rpm reading is reading high, and it also shows an rpm decrease when I increase power. It was working great about two weeks ago, only thing that changed between now and then is we replaced the oil pressure wire on the probe. The wire for the rpm is connected to the p-lead. Any ideas on where to look or how to fix it would be greatly appreciated. I have a jabiru 3300 and a rdac xf in my plane.

[sonex892.]

Hi The Rdac XF has 3 Dip switches to select FIlter, Ballast and high gain plus a sensitivity potentiometer. If you are connected to the P lead for the tacho you pressumably have a 10k resistor.

First make note of all the current switch positions on the RDAC

Try adjusting the sensitivity gain adjust to see if that helps

These are the dip switch positions I think you should have selected when using the P lead
Noise filter ON
Ballast resistor OFF
High gain OFF

[Bluth125]

Ok, I will check the switches. I am pretty sure I don’t have a resistor in line from the p-lead so I will also try that.

[peter anson]

You definitely should have that 10K ohm resistor in series. See page 27 of the RDAC manual. If you didn't do the connection it might only appear as a small bump in the wire covered with heat shrink. You should also check that the reference ground is grounded to the engine.

Peter