Hi Guys,
I have an old Narco 810/Flightcom 403 combination that's worked well for almost 50 flights . Recently , I've started getting a buzzing noise while transmitting . Reception is 5/5 .
Here's what I've tried so far:
- Re-racked the radio and confirmed that that BNC connectors are mated properly . Did not actually check continuity .
- Turned one mag off at a time while transmitting . No change . Can a mag still make noise if it's not turned on ?
- Turned off internally regulated ND alternator . No change . Can an alternator still make noise if not supplying voltage to the bus ? Bearings etc ?
- Turned off all lights and other avionics . No change .
So , I've tried a number of things and am running out of ideas . I have made a few observations about when and how it makes noise . I have a CS prop and there is very little noise at 2700 but the intensity of the buzz increases and the frequency decreases when I lower prop RPM . Also on final with the power pulled back almost to idle there was very little noise .
A few thoughts for continued trouble shooting ......
-Try different MP with a given prop RPM . May indicate an ignition system link but I thought I ruled that out by isolating mags ...
-I'm wondering if the different RPM affect might have to do with a difference in the vibration frequency affecting a loose conection , wire , antenna etc .
I may try putting my hand under the panel to check for vibration and maybe dampen it if there is .
Any suggestions are appreciated ! Unfortunately I have to jet off to the Orient so I won't be able to try all your very helpful suggestions until the weekend . Ultimately I want to modernize my panel but I would like to get the present system back in order until I do.
Marc
I have an old Narco 810/Flightcom 403 combination that's worked well for almost 50 flights . Recently , I've started getting a buzzing noise while transmitting . Reception is 5/5 .
Here's what I've tried so far:
- Re-racked the radio and confirmed that that BNC connectors are mated properly . Did not actually check continuity .
- Turned one mag off at a time while transmitting . No change . Can a mag still make noise if it's not turned on ?
- Turned off internally regulated ND alternator . No change . Can an alternator still make noise if not supplying voltage to the bus ? Bearings etc ?
- Turned off all lights and other avionics . No change .
So , I've tried a number of things and am running out of ideas . I have made a few observations about when and how it makes noise . I have a CS prop and there is very little noise at 2700 but the intensity of the buzz increases and the frequency decreases when I lower prop RPM . Also on final with the power pulled back almost to idle there was very little noise .
A few thoughts for continued trouble shooting ......
-Try different MP with a given prop RPM . May indicate an ignition system link but I thought I ruled that out by isolating mags ...
-I'm wondering if the different RPM affect might have to do with a difference in the vibration frequency affecting a loose conection , wire , antenna etc .
I may try putting my hand under the panel to check for vibration and maybe dampen it if there is .
Any suggestions are appreciated ! Unfortunately I have to jet off to the Orient so I won't be able to try all your very helpful suggestions until the weekend . Ultimately I want to modernize my panel but I would like to get the present system back in order until I do.
Marc
