High pitch noise in overhead speaker.

[FloridaMan]

Working through some electrical gremlins in the new rocket. Here is the symptom of one of them: Battery fully charged. Master On. High pitch noise through overhead speaker. Avionics master on. Noise goes away. 

Battery less than fully charged (there is a drain we are still chasing). Master on. High pitch noise even louder. Avionics master on. Noise stays; doesn’t matter if engine is running or not. 

Battery so low it can’t start the engine. Master on. #2 COM illuminates even though avionics master is off. I suspect there is a lockout somewhere or an unusual relay circuit that piggybacks that depends on a reference or differential voltage that is allowing this. 

Noise does not appear tied to any radio or intercom. If I turn everything in the stack off, it stays. If I pull the 50A Aux bus breaker, it goes away. 

[Yetti]

filter capacitor in some device gone south.   Pull breakers till you find it.

[N201MKTurbo]

Are you sure it isn't one of the sonalerts?

[FloridaMan]

3 hours ago, N201MKTurbo said:

Are you sure it isn't one of the sonalerts?

Come to think of it, I noticed the stall warning had been a bit hyperactive in flight and now I’m not noticing it at all in the flare. The DME is also INOP and it wasn’t when I first test flew the plane. I suspect something got bumped during prebuy and it could all be related. 

Is there anything other than stall, gear and AP that would beep in a 1981 m20k?

[carusoam]

Electronics on when the Avionics Master is off...?

Something to look into...

1) The Avionics Master is a fail closed mechanism...

2) It opens when the master relay is closed...

3) It closes again when you turn the Avionics master on...

4) This gives you a hint how some of the noise is coming and going when the Master is on and off... and the Avionics master is on and off...

Something seems amiss about the Avionics master... I think you may have found what may be draining your battery...

The Master solenoid seams to be not opening completely when turned off, when the unpowered Avionics master closes, power is draining out to at least one radio...

Somebody recently posted the electrical drawings of one of the post modern era Mooneys... Complex is a gentle word to describe them...

See if you can find them being discussed...

Best regards,

-a-

[FloridaMan]

It was the stall warning vane. Went down to plane, raised and lowered it a few times and the noise went away. It sure was annoying. 

[Bartman]

17 minutes ago, Antares said:

It was the stall warning vane. Went down to plane, raised and lowered it a few times and the noise went away. It sure was annoying. 

Spray liberally with electrical cleaner

[FloridaMan]

Here’s a new one. The alternator field breaker tripped today in flight so I returned to base. With the engine off, the breaker trips immediately when I turn the master on. It’s a hartzell direct drive (no belt) alternator. The alternator is a bit noisy and on a recent flight I noticed it stopped charging briefly. My IA inspected the brushes and noted there was no filter on the output.  

I’m starting to suspect that the battery discharge gremlin that I’m experiencing may just be bad batteries that could have also cooked my alternator, or an alternator that has been struggling to keep the batteries charged. 

[milotron]

Do you have multiple batteries? You are 14V system still, correct?

What is charging current, voltage like?  The "field" circuit breaker is really just power to the voltage regulator. Maybe that is done?

 

iain