I own a 2015 Alpha Trainer with about 1200 hrs on hull\engine (Rotax 912UL). Plane has a Kanardia instrument suite installed and all data is passed through the CAN bus.
Recently I was having an erratic engine gauge problem that couldn't be isolated.  


I thought the DAQU was bad and sent it back for troubleshooting and repair.  They couldn't find an issue with it but recommended i upgrade to the latest version.  Installed the new DAQU and thought everything was fine, then after about 20min run time the erratic engine gauges came back.
Sent it to a long time A&P and found a melted rectifier plug & connector.




After replacing the rectifier and associated wires, it appeared to function properly for about 7 hours and now the erratic engine gauge issue appears to be back.  We have tested all the other wiring along with verifying all the grounds on the plane and engine.  As you can see in the picture that the rectifier was replaced in Aug 2023 due to a continued low voltage issue.  The only thing that wasn't tested, as I remember, was the capacitor on the output side of the rectifier.

Has anyone experienced this issue to seen this before.  

Thanks for any assistance or direction anyone could provide.

  • Re: Erratic Gauges

    by » 5 weeks ago

    Can you measure the supply voltage to the DAQU when it is showing unstable values? As well as measuring the DC voltage swith your multimeter to ACV and measure the AC component, it should be quite low < 0.5V.

    Does the fauly show itself while you are on the ground? If so, can you tug on the wiring harnesses and tap the various sensors/modules to see if there is a mechanical problem?

    CAN is fairly noise immune but if there a bad connection on the bus wires then that can give you erratic data. It might be worth looking at the data cables. Have you got some others that you could substitute or swap with others to see if the fault moves?


  • Re: Erratic Gauges

    by » 5 weeks ago


    I can see if I can get setup to measure those items, could you provide a bit more detail about where to read the ACV AC components.  I do not have an extra CAN cable but I could easily make one if I knew the PIN out.  Standard CAT 5\6 network cable should work, right?

    I do have the suspected BAD one that I took out last August and could bench test it if there was a way.

    I personally haven't seen the issue during ground runs, but I've heard they are currently happening.  the idea of moving wires around behind the dash was considered, but difficult (not impossible) with some items mounted to the glare shield.

    thanks for the help and recommendation


  • Re: Erratic Gauges

    by » 5 weeks ago

    My thinking with the AC voltage measurement was to check to make sure that the generator is outputing a nice stable DC voltage, about 14V. What you don't want is a 2V AC ripple on the DC voltage supplying the DAQU.

    You might be able to get away with a straigh through Ethernet cable but a crossover cable will not work.

    My other thoughts would be what items are unchanged in the system? What items have been manipulated but not changed? Which of the gauges are giving unstable readings?

  • Re: Erratic Gauges

    by » 5 weeks ago

    hate to burst anyone's bubble...the 912UL has no CAN wiring, it is all analog. 

    The 2 wires, G on the regulator, have not been connected correctly.  They have a gap or the blade connector is loose.  The generator can produce far more than 12 Volts here and is not regulated until it exists the R and B+ terminal of the regulator.  



  • Re: Erratic Gauges

    by » 5 weeks ago

    Wizard I think you misunderstand. The sensors in the engine are indeed analogue but their output is monitored by a Kanardia DAQU (Data Aquisition Unit) that digitises the signals before passing them to the EFIS/EMS using a fully digital CAN bus. Depending on the level of error detection/correction in the system, any problems with the CAN bus will result in data corruption that could lead to erratic gauge readings on the display. This is not an old school installation with steam gauges like my plane ;-)

    I would dearly love to install the Kanardia system into my Eurostar, it would be the perfect solution but the cost is over 10% the value of the plane, \aso unless someone wants to donate one to me I'll be stuck with what I've got :-(

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