Strange Electrical Problem

[Guitarmaster]

Time to put the collective Mooneyspace mind to work.

The problem is, when the master switch is on, the stall warning works as advertised.  With the master off, the piezo horn makes an odd, faint "cracking" sound.  It goes away when the master is on.  It also goes away when the stall vane is activated or the contacts on the piezo are shorted.  In other words, when the circuit is grounded and the master off, no noise, but ungrounded, weird cracking noise.  I you move the vane with the master off, the piezo will click.

The noise also disappears when the Stall Warn breaker is pulled.

To re-cap:

Master on:  All is normal.
Master off:  Weird, faint crackling noise from the piezo.
Master off stall vane activated:  No Noise.
Master off, Stall Warn breaker pulled: No noise.

I thought there might be some stray voltage somewhere, but all circuits (except the dome light) are dead.

Side note to this, when flying in the rain, the stall horn will come on faintly.  I get this as the water is probably creating a weak ground and hence the weak sound.

Before I get into pulling the stall vane I wanted to pick your brains.

[Marauder]

You do come up with some interesting problems.

If the master is off, the stall circuit should be deactivated. The fact that you are hearing something suggests you are getting some leakage.

Here is what I would do:

You should be able to swap the Sonalerts between the gear warning and the stall warning to see if it is repeatable. I would replace the Sonalert before digging into the stall vane and switch assembly.

It does sound like a voltage leak but where could it be coming from? I have replaced my Sonalerts. They are not very expensive in airplane terms.

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[Yetti]

My overhead light is powered up when the master is off.   There is always on live voltage up there by the stall warning.  Just saying

[Guitarmaster]

16 minutes ago, Yetti said:

My overhead light is powered up when the master is off.   There is always on live voltage up there by the stall warning.  Just saying

That's the only place it could be coming from.  

 

[Guitarmaster]

41 minutes ago, Marauder said:

You do come up with some interesting problems.

If the master is off, the stall circuit should be deactivated. The fact that you are hearing something suggests you are getting some leakage.

Here is what I would do:

You should be able to swap the Sonalerts between the gear warning and the stall warning to see if it is repeatable. I would replace the Sonalert before digging into the stall vane and switch assembly.

It does sound like a voltage leak but where could it be coming from? I have replaced my Sonalerts. They are not very expensive in airplane terms.

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I agree on the leakage, but from where?  Swapping the Sonalerts is my next step.  When yours quit, was it making weird noises or just didn't work?

As far as the interesting problems... go big or go home!  I tried the chant and dance, but the gremlin is still there.  Perhaps I am doing it wrong?

Edited March 3, 2016 by Guitarmaster

[Marauder]

41 minutes ago, Marauder said: You do come up with some interesting problems.

If the master is off, the stall circuit should be deactivated. The fact that you are hearing something suggests you are getting some leakage.

Here is what I would do:

You should be able to swap the Sonalerts between the gear warning and the stall warning to see if it is repeatable. I would replace the Sonalert before digging into the stall vane and switch assembly.

It does sound like a voltage leak but where could it be coming from? I have replaced my Sonalerts. They are not very expensive in airplane terms.

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I agree on the leakage, but from where?  Swapping the Sonalerts is my next step.  When yours quit, was it making weird noises or just didn't work?

As far as the interesting problems... go big or go home!  I tried the chant and dance, but the gremlin is still there.  Perhaps I am doing it wrong?

Key is keeping the left foot elevated at least 18" while conducting the chant.

It has been a decade since I replaced them, but I think my stall horn died and I decided to replace them both. I think they were in the $15 to $20 range each.

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[kortopates]

Can't be a Sonalert - they don't generate their own electricity. Since the circuit is picking up some current from somewhere I would be looking for a chaffed wire. I'd start by seeing if the voltage is measurable at the Sonalert (obviously with master off) and then start tracing back. Without a measurable potential at the Sonalert to have a signal to narrow it down it could be really hard to find. Sometimes evidence of arcing will highlight it. It seems plausible the dome light power wire could be the source hitting the Sonalert circuit somewhere. Good luck!

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[jamesm]

What year is your Mooney?  On my 67'C the stall warning and gear  warning  comes from the same unit  physically two different units but  separate circuits (I think).  Is it possible you  broken or loose connection stall/gear warning horn? like a broken ground?  If the wiring is original I would check the all electrical connections and make sure ground connections are clean.  Here  is a wild  hypothesis for you....  If  your stall/warning are same unit may be either water gotten in the unit some how or what you could be hearing is the gear warning chirping and moving airplane is causing  horn to go off. If you  do have common gear/stall warning . Maybe  when you have the master s/w on the required connection is made it's counter part. another wild  guess  if  have  the original circuit breaker(s) original could be the circuit  breaker could be  intermittent.

 

James '67C

 

[Guitarmaster]

24 minutes ago, jamesm said:

What year is your Mooney?  On my 67'C the stall warning and gear  warning  comes from the same unit  physically two different units but  separate circuits (I think).  Is it possible you  broken or loose connection stall/gear warning horn? like a broken ground?  If the wiring is original I would check the all electrical connections and make sure ground connections are clean.  Here  is a wild  hypothesis for you....  If  your stall/warning are same unit may be either water gotten in the unit some how or what you could be hearing is the gear warning chirping and moving airplane is causing  horn to go off. If you  do have common gear/stall warning . Maybe  when you have the master s/w on the required connection is made it's counter part. another wild  guess  if  have  the original circuit breaker(s) original could be the circuit  breaker could be  intermittent.

 

James '67C

 

The plane is a '75.  I did think this was a possibility, but the gear and stall warning circuits are completely different circuits.

[Guitarmaster]

1 hour ago, kortopates said:

 

Can't be a Sonalert - they don't generate their own electricity. Since the circuit is picking up some current from somewhere I would be looking for a chaffed wire. I'd start by seeing if the voltage is measurable at the Sonalert (obviously with master off) and then start tracing back. Without a measurable potential at the Sonalert to have a signal to narrow it down it could be really hard to find. Sometimes evidence of arcing will highlight it. It seems plausible the dome light power wire could be the source hitting the Sonalert circuit somewhere. Good luck!

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There is no measurable voltage at the Sonalert.  When I pull the breaker, it goes away.  When I short across the terminals it goes away.  If there is stray voltage, it's got to be coming through stall circuitry.  The dome light circuitry appears normal.  There is no change in the sound with turning the dome on or off.

 

[kortopates]

They are different entirely with different kinds of Sonalerts. The stall is a continuous tone while the gear is a pulsating tone. If not then you'd have the wrong unit installed.

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[irishpilot]

Does your plane have newer instruments, 530W, GNS, etc?  I found that my plane had a some "creative" wiring with the 530W that had to be fixed.

[kortopates]

1 hour ago, kortopates said:  

Can't be a Sonalert - they don't generate their own electricity. Since the circuit is picking up some current from somewhere I would be looking for a chaffed wire. I'd start by seeing if the voltage is measurable at the Sonalert (obviously with master off) and then start tracing back. Without a measurable potential at the Sonalert to have a signal to narrow it down it could be really hard to find. Sometimes evidence of arcing will highlight it. It seems plausible the dome light power wire could be the source hitting the Sonalert circuit somewhere. Good luck!

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There is no measurable voltage at the Sonalert.  When I pull the breaker, it goes away.  When I short across the terminals it goes away.  If there is stray voltage, it's got to be coming through stall circuitry.  The dome light circuitry appears normal.  There is no change in the sound with turning the dome on or off.

 

Are you measuring with the stall vane closed/up? That switch has to be closed to complete the circuit and get your click noise (from what I understand you said earlier)

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[Guitarmaster]

1 minute ago, irishpilot said:

Does your plane have newer instruments, 530W, GNS, etc?  I found that my plane had a some "creative" wiring with the 530W that had to be fixed.

No.  Circa 1994 instrumentation.

 

[Guitarmaster]

Just now, kortopates said:

Are you measuring with the stall vane closed/up? That switch has to be closed to complete the circuit and get your click noise (from what I understand you said earlier)

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No.  With the stall vane down.  Lifted ground.  When the vane is up, grounded, the sound goes away.  I didn't think about measuring voltage with the stall vane closed.  I will try that tomorrow.

[kortopates]

Maybe I miss understood but I thought that was when it "clicked" - pulling it up to close. But the idea to measure a voltage at the same time it makes the click noise. It's hard to believe it could do that without at least a small voltage on it - but I am assuming too small of one to cause it generate its normal tone.

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[Yetti]

The light has a bare wire resistor soldered to the low setting.....  I though about using a bunch of shrink wrap to fix things up.   You also have antennas that could have lost their ground, There is also static electricity... st. Elmo

[N601RX]

If I remember correctly the switch to the master relay completes the circuit to ground to turn on the master relay.  So when the master switch is off this wire/ switch terminal will have battery voltage on it.  It would still have to find a way to get to the alerts.

[Guitarmaster]

At this point, I think it may be aliens trying to contact me through the stall warning system.

[takair]

Mike is right, there is voltage at the master until it makes ground.  Another possibility is radio memory.  For example, a Narco MK12D uses and after all power source...battery....to hold up its memory.  There are also a few clocks out there that use hot battery bus to keep time.  Do you have any of these things?  How does your battery hold up between flights?  Do you use a battery minder?  Does the crackle go on indefinitely or will it taper off after a few hours?  

[Guitarmaster]

21 minutes ago, takair said:

Mike is right, there is voltage at the master until it makes ground.  Another possibility is radio memory.  For example, a Narco MK12D uses and after all power source...battery....to hold up its memory.  There are also a few clocks out there that use hot battery bus to keep time.  Do you have any of these things?  How does your battery hold up between flights?  Do you use a battery minder?  Does the crackle go on indefinitely or will it taper off after a few hours?  

I agree it has to be stray voltage... however, what I don't get is why it goes away when the stall vane is grounded.  I would think it would have the opposite affect and get louder.

I have a clock a KLN89 and MX170C radios.  This problem started about three months ago.  The crackle/sizzle goes on indefinitely.  I have left it for multiple days with no noticeable depletion of the battery.  I don't use a battery minder.

I have inspected all the wiring and can't find any evidence of chafing.

[Guitarmaster]

See how this tastes....

Do you all think I could be dealing with a ground loop?  With potential at the master and a lousy ground somewhere creating a "loop" and picking up from the hot wire or stray electricity in the air?

Edited March 4, 2016 by Guitarmaster

[Marauder]

See how this tastes....

Do you all think I could be dealing with a ground loop?  With potential at the master and a lousy ground somewhere creating a "loop" and picking up from the hot wire or stray electricity in the air?

I think you didn't do the chant.

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[Guitarmaster]

I did the chant. But I think I had my right leg up and only about 16" off the ground. Will redo in the morning.

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[Marauder]

When I first got my Mooney I had a number of weird electrical issues. I spent hours tracing leads, cleaning Molex connectors and cleaning ground contacts. Your problem fits into that "1975 Executive Handbook of Unusual and Bizarre Issues".

I think weirdest one was some failed diode that was soldered in one of the lines under the panel. I can't remember what the issue was, but I remember finding the diode nicely wrapped up in the wire bundle and shrink wrapped in place. And it had failed.

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