I believe most IO550 tach pickups are from a magneto and that there's no other electronic crank position indicator.  The elements common to your three glass panels probably are the wire running from a magneto lead and some sort of A/D converter.  On Jan 18, 2013, at 2:04 PM, Berni Breen wrote:

I just started experiencing widely varying RPM read outs on all 3 of the gauges of my Lancair Legacy.  During run up and subsequent take off my MFD, PFD and EIS all show correct RPM read outs.  Not until I get into cruise and set the prop to 2400 do I see the problem.  I slowly begin to see all 3 of the read outs start to show a 2300 to 2600 (or there abouts) variance.  All 3 gauges are in sync and agreement on the numbers.  In other words, they all 3 read the same thing and the variance is very rapid up and down.  Since I have already concluded that the prop governor is functioning properly and I do not feel or hear a prop pitch change during these occurrences, I am all but 100% sure I have some sort of erroneous information being sent to my "glass" and therefore erroneous readings.  As such I believe I need to check all of the wiring and or "pick ups" between the engine and my MFD, PFD and EIS.  My problem is that I am not familiar with any of that.  Can someone reading this please help me get started by suggesting where I should look for the source of where my equipment gets the RPM information from the IO550 (location of pick up)?  Further, any kind of procedure to track down where or what my problem might be would be most appreciated.

BTW, my read outs are on my GRT HX MFD and PFD as well as my VP200.  I know these units are displaying what they believe to be accurate information as everything else is functioning flawlessly.  I removed my prop governor, sent it for overhaul and it checked out perfect.

Sent from my iPad
Berni Breen
Bbreen@cableone.net
--
For archives and unsub http://mail.lancaironline.net:81/lists/lml/List.html