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Berni,
I had the same experience few months back with my Legacy. For no reason at all, I started seeing strange and erratic rpm readings on my Dynon system. It was obvious that the engine was fine, i.e. no over speed or change in power experienced. The problem gradually got worse as we conducted flight tests and tried to find the cause. During one of my test flights, without any warning, the rpm stabilized and started functioning properly. After landing and visual inspection, I decided to go for another flight to see what I would find out. During the run-up, the magneto test failed. The magneto had less than 100 hours on it after the 500 hours inspection/repair. The magneto was removed and sent to the shop for further evaluation. The repair shop called me and said that the magneto had check out ok with no problems. I was adamant about the magneto having failed during run-up and asked him to heat the unit while testing. I received a call from the shop shortly that the magneto had indeed failed after having it heated up. It was determined that the coil was the problem and it was replaced and the unit was installed in the airplane and has been working just fine ever since. That was my experience with a similar problem. I hope this helps.
Henry Arjad N22YY KSNA -----Original Message-----
From: Lancair Mailing List [mailto:lml@lancaironline.net] On Behalf Of Berni Breen
Sent: Friday, January 18, 2013 12:04 PM
To: lml@lancaironline.net
Subject: [LML] RPM on IO550N
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
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