Headset Noise Issues and Master Relay Location

[Mush]

I've been chasing gremlins trying to solve what is causing headset squeal in non-ANR hearsets and flutter in noise cancelling headsets. This happens with the engine running and also sitting on the ground not running. I installed a brand new Garmin SL-40 radio, new PS Engineering PM1000II intercom, new RA Miller AV-529 antenna, new RG142 double shielded antenna cable, new radio/intercom/transponder/ av master circuit breakers. All ground are clean and solid. Well, $2500 later the issues are still there. Basically everything from the wing root forward to the panel has been changed.

I'm starting to think it may be coming from the master switch or the master relay, but the issue is I can't find the relay. My plane is a 1968 PA-18 with serial number 18-8721. I believe everything from the wing root back to the battery is original including the wiring. When looking at the battery box location there is the battery which leads to a small block with two fuses (primary/alternate), that then runs to both the starter relay and also up the the master switch in the right wing root fairing. So is it possible they didn't use a master relay on the 1968 model or is it located somewhere else. Also, has anyone seen a bad relay or switch generate noise in a headset?

Another note, I can turn the noise cancelling heatsets on and have everything completely off including the master and the headsets will flutter when I move my head near the right wingroot.

I really think it may be time to rip everything out from the wingroot back and just install the Atlee Dodge underseat battery, but then again there are places to go coming up real soon.

 

[mike mcs repair]

... Also, has anyone seen a bad relay or switch generate noise in a headset?
....

Yup, found bad/burnt contacts in a master solenoid.... use a jumper wire to bypass it to test... if the part you bypass makes noise go away, you found your problem, quick, simple and cheap...

thats always my first step hunting noise... and all it costs is a chunk of wire.....

I would guess master switch with what you describe, since you do NOT have a solenoid for master, or dirty fuse block holder or one of the connections there.. sand & lube all connections..

 

[Mush]

Geeze Mike, if it turns out to be a .25 cent fuse after spending $2500 on an all new comm set-up I'm going to be sick. Actually, I really needed a new radio and the Garmin SL-40 is pretty sweet compared to the old Narco Com 120. I sure hope you are right about the fuse. I'll give it a shot and report back. Also, The parts manual shows my set up as well as the set up with the master relay. Do you simply replace the fuse block with a master relay?

 

[mike mcs repair]

... Do you simply replace the fuse block with a master relay?

yes, you usually needed to go to a relay when you put the big 60 amp alternators in...(fuses were only good to 30 amps..)

 

[Steve Pierce]

All relays I have seen in factory Super cubs have been at the battery box and one in the right wing root.

 

[Mush]

Well, I tried cleaning everything in the battery box area but no joy. I called Univair to check on a replacement master switch P/N AN3023-1 but decided to do some more research after hearing the $120 price tag. I am planning on doing the B&C alternator conversion and starter swap in the near future and was pretty sure the stock master had to be switched with the alternator conversion. Called B&C and he confirmed it. Now I just need to find a servicable stock master to see if its my problem.

 

[evroosevelt]

Is a SC master switch anything like a PA12 master Sw? If so I have one I would send you.
EV
evroosevelt@hughes.net

 

[Mush]

Thanks for the offer, email sent.