Hi Victor,
i am new Member, just after reading your Problem.
There is a 100% solution, i had solved this problem in an 914 Installation in a Europa XS.
There i can hear the same electric noise in Headset, when Radio is on. Turning the ACU of 914 on, the servo starts ist self test, this is the first time, you can hear the noise of the running servo Motor, and by each Action of the servo.
As an Engeneer, i remarked this as a no-go-item in a good electrical Environment of the aircraft.
The trouble can be measured by handheld Radio icom etc and with an spectrum analysator. The electrical noise is broadband, so it will be caused by electrical sparks in an electric DC-Motor without any filtering of elecric noise.
If possible, unsrew your servo-unit. There you can see a very simple electric DC-Motor 12V with plastic gear to drive the Wastegate Cable.
I was confused, because there was nothing to see, that looks like a capacitor or a filter-network with ferritcoils.
These minimum filtering you can find in every Installation in the world like cars or Machines or electrical toys, to be able for electrical radio-noise certification.
The solution i made was very simple, a small capacitor of 100 nF and a Voltage Range over 50 V, with optimal mechanical dimensions, is soldered direct on the printboard, on the 2 contacts, which are connected to the brushes of the little 12 V- Servomotor.
After this action, no electrical noise was heared, becaus the noise is direct filtered at his source at the motor brush contacts.
I had proposed this very easy Change to Rotax, but there i was ignored, with Problems of the certification.
The solution of Rotax is a very complex and expensive shielding of all wires to the servo-unit.
But this is the wrong way, the noise had to be distroied at his source, the firing collectorbrushes of the DC-Motor.
My Installation with this little capacitor works fine, no electrical noise can be heared, the problem is solved for every time.
This capacitor can be helpful for all 914-users, because there is not built in any filtering.
Unbelieveable for an certified aircraft-installation
I wish you good luck by solving this problem.
Let me know, if you do this . . .
Walter
