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Avionics Master Switch?


eft
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Also check the switch… and it’s relay…

In Modern Mooneys… a failed avionics switch is supposed to be wired in a failure proof mode….

if the relay is working correctly… the avionics bus will be live when the master comes on…

If the relay is not working…. It may be stuck in the off position…

 

Failed relays is why European Mooneys get an extra switch/relay to power the avionics bus…. In case the first one fails…

Relays don’t last forever….

 

PP thoughts only…

Best regards,

-a-

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Look at this old post.  A failed avionics switch in a 12-V J leaves your avionics in an ON position.  
 

A failed relay, on the other hand, can either result in power ON to your radios or no power to your radios- dependent on the fail mode of the relay. 
 

looks like the illustrative pictures were lost in one of the server migrations perhaps. 

I’d definitely check the wiring schematic to see if the K uses the same relay circuit 

I might have a radio switch for a K in my garage.
 

b   

 

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Hey Mooney owners, my problem is running deeper. First some context:

  • The problem began with failure of the landing gear to extend (used emergency manual extension). All systems associated with the gear have been confirmed to be operation properly and the gear problem was resolved and the gear operated UNTIL it wasn't and broken wires on the "gear override switch" were found to be loosely connected. These were repaired and the gear still doesn't operate. Bummer.
  • Working on that issue we discovered that with the Avionics Master Switch in the OFF position, the avionics turned on. That led to the replacement of the switch with no change. Bummer. I think that a replacement of the Radio Master Relay is the next step.
  • And, we also discovered that the panel annunciator lights would not illuminate in the TEST mode or in a "right low fuel", "left low fuel", "high/low volts", or  "low vacuum" situation. The "gear locked" and "gear unsafe" illuminate properly. 
  • Most recently we had the "auxiliary bus" breaker pop after about 5 seconds. We haven't worked on that issue yet.

Can't figure out the reason for a combined failure of the gear control, annunciator problems, and avionics master circuit.  Anyone have any insights?????

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8 minutes ago, eft said:

Can't figure out the reason for a combined failure of the gear control, annunciator problems, and avionics master circuit.  Anyone have any insights?????

That's a lot of electrical problems in a short time.  I see that you are new to MooneySpace (Welcome!), and I'm wondering if you are new to this airplane as well.  You may not know, and may not be able to discern from the logs, but I wonder if this airplane has been exposed to an environment that could attack a lot of electrical connections at once?

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I recently had a problem with erratic low voltage then the main breaker tripped and the alternator went off line, accompanied by a burnt wiring odor.  For months the strobes being tuned on caused the voltage to fluctuate by about one volt.

Previous troubleshooting showed the alternator,  firewall forward wiring and regulator good.

This time I began at the main breaker suspecting a loose connection at the breaker. After removing the glare shield, in the next five seconds I found the jumper from the main 70 amp breaker was loose at the neighboring 50 amp aux buss breaker.  Loose as in about to fall off loose.  Yes it got hot, melted insulation, it just surprised me a loose connector would cause the main to trip. The jumper is that three wire piece Mooney put together to go from the main breaker to the aux buss, landing light and gear.

Repaired, all is well.  No more jumpy voltage when the stones are turned on.

Without looking at the electrical schematics for your plane, I suspect a loose connection could affect everything you describe.

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The AUX BUS breaker protects the wiring to the AUX BUS which is the bus that powers the circuit breaker rocker switches for lights, boost pump, radio relay, etc. If the AUX BUS breaker pops, there is a short somewhere. Also, if the AUX BUS breaker pops, the avionics will power up because the relay that powers the AVIONICS BUS will lose the control power that keeps it OFF.  The annunciator panel and the landing gear are powered from the BATTERY BUS, not the AUX BUS. There landing gear lights are powered through the GEAR WARNING circuit breaker whereas the other annunciator lights are powered by the ANNUNCIATOR circuit breaker. It seems unlikely that all these symptoms are caused by a single fault, but it will take some detailed troubleshooting with the schematics in hand to determine the root cause(s). 

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3 hours ago, eft said:

Hey Mooney owners, my problem is running deeper. First some context:

  • The problem began with failure of the landing gear to extend (used emergency manual extension). All systems associated with the gear have been confirmed to be operation properly and the gear problem was resolved and the gear operated UNTIL it wasn't and broken wires on the "gear override switch" were found to be loosely connected. These were repaired and the gear still doesn't operate. Bummer.
  • Working on that issue we discovered that with the Avionics Master Switch in the OFF position, the avionics turned on. That led to the replacement of the switch with no change. Bummer. I think that a replacement of the Radio Master Relay is the next step.
  • And, we also discovered that the panel annunciator lights would not illuminate in the TEST mode or in a "right low fuel", "left low fuel", "high/low volts", or  "low vacuum" situation. The "gear locked" and "gear unsafe" illuminate properly. 
  • Most recently we had the "auxiliary bus" breaker pop after about 5 seconds. We haven't worked on that issue yet.

Can't figure out the reason for a combined failure of the gear control, annunciator problems, and avionics master circuit.  Anyone have any insights?????

 Are you working with an A&P?

  • Do you or he have the Service Manual and Parts Manuals?
  • The electrical schematics start on page 527.  All the electrical parts are listed in the Service Manual (not in the Parts Catalog).
  • The parts catalog used to be online but I can't find it now.
  • Based on your earlier switch number it sounds like you have a 12V model.  There are 17 different schematics depending upon the serial number
  • You should be able to test the switch and other items with a VOM before replacing.  It sounds like your original switch may be good.

Also on the landing gear, you need to test the Airspeed Safety Switch - it may not be the wiring.  Here is the same problem currently on a K.

Edited by 1980Mooney
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Thanks for the additional feedback! Responding to the multiple comments:

  • I have owned and operated this airplane for 27 years and prior to that it was based in Texas and New Mexico. My home base mechanic (who has been assisting with troubleshooting) has maintained the aircraft for most of those 27 years
  • I have a Mooney Maintenance Manual and Parts Catalog and have been referring to them frequently. I have reached out to the avionics shop that did the most recent work (GTN 650 and CGR 30P) for schematics when they did these installs in 2013 and 2014.
  • This is a 12v serial # 65 airplane
  • The airspeed safety switch has been tested and is operating properly

I have made copies of relevant sections of the electrical schematic and traced everything. The shop will get that in the morning. 

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EFT,

Congrats on your long term Mooney ownership..!

The one thing that stood out was your surprise when the avionics were on with the Avionics Master off…


I have only owned a Mooney for 20+years…

And I know that the avionics master is wired in a fail proof way… :)

So if you fail the avionics switch… it is highly probable to get power to the avionics bus… because the avionics relay is normally closed (NC) in electronics terms..

 

This is an old standard, that is going to cause confusion… unless your electronics guru is aware of what to look for…

You are stuck in the middle region where your mechanical guru may not be an electrical guru…

This isn’t Mooney specific stuff either….

 

Things to look for…

1) Master switch off… avionics relay is closed (unpowered this relay is normally closed!)…

2) Master switch on… avionics relay opens….

3) Master and avionics switch on…. Avionics relay closes again. (Avionics power up as normal…)

 

Avionics switch fails over night, prior to next flight, wears out, snaps in two…. Or just wants to be a pain… or the avionics relay doesn’t get powered from the Master…

4) Master on, Avionics relay fails to open up. (remember the avionics relay begins in failed closed mode as designed)

5) avionics master on, fails to cut power to close the avionics relay again…. Avionics switch fails to power the avionics relay… (so it stays closed)


It sounds like your mechanic may not…

6) Have the knowledge of these relays, where they are, or maybe how they are wired…

7) Know the avionics bus is powered when the combination of relays are both powered…

 

Mooney gurus like to bet on things like….

I bet you lunch… I can turn the avionics on without turning on the avionics master switch….

Upon placing the bet…. They fail the breaker that powers the avionics relay… it magically fails closed…. The avionics all come to life.

 

If you know how this all works…. Your mechanic will owe you lunch… :)

Spread the word…

 

If this all makes sense… and helps your mechanic fix the myriad issues that have since arisen….  I like lunch too… :)  Send the lunch money to MS and get your supporter badge! :D

PP thoughts only, challenged by describing the matrix of normally closed relays vs. normally open relays…

Best regards,

-a-

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16 hours ago, carusoam said:

EFT,

Congrats on your long term Mooney ownership..!

The one thing that stood out was your surprise when the avionics were on with the Avionics Master off…


I have only owned a Mooney for 20+years…

And I know that the avionics master is wired in a fail proof way… :)

So if you fail the avionics switch… it is highly probable to get power to the avionics bus… because the avionics relay is normally closed (NC) in electronics terms..

 

This is an old standard, that is going to cause confusion… unless your electronics guru is aware of what to look for…

You are stuck in the middle region where your mechanical guru may not be an electrical guru…

This isn’t Mooney specific stuff either….

 

Things to look for…

1) Master switch off… avionics relay is closed (unpowered this relay is normally closed!)…

2) Master switch on… avionics relay opens….

3) Master and avionics switch on…. Avionics relay closes again. (Avionics power up as normal…)

 

Avionics switch fails over night, prior to next flight, wears out, snaps in two…. Or just wants to be a pain… or the avionics relay doesn’t get powered from the Master…

4) Master on, Avionics relay fails to open up. (remember the avionics relay begins in failed closed mode as designed)

5) avionics master on, fails to cut power to close the avionics relay again…. Avionics switch fails to power the avionics relay… (so it stays closed)


It sounds like your mechanic may not…

6) Have the knowledge of these relays, where they are, or maybe how they are wired…

7) Know the avionics bus is powered when the combination of relays are both powered…

 

Mooney gurus like to bet on things like….

I bet you lunch… I can turn the avionics on without turning on the avionics master switch….

Upon placing the bet…. They fail the breaker that powers the avionics relay… it magically fails closed…. The avionics all come to life.

 

If you know how this all works…. Your mechanic will owe you lunch… :)

Spread the word…

 

If this all makes sense… and helps your mechanic fix the myriad issues that have since arisen….  I like lunch too… :)  Send the lunch money to MS and get your supporter badge! :D

PP thoughts only, challenged by describing the matrix of normally closed relays vs. normally open relays…

Best regards,

-a-

Outstanding description! I have had my K model for 6 months but had no idea that is how the system is set up. Fortunately I have had no problems, but if one should develop at least I will now have an idea of what could be occurring.

Torrey

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Thanks for the additional feedback! Responding to the multiple comments:

  • I have owned and operated this airplane for 27 years and prior to that it was based in Texas and New Mexico. My home base mechanic (who has been assisting with troubleshooting) has maintained the aircraft for most of those 27 years
  • I have a Mooney Maintenance Manual and Parts Catalog and have been referring to them frequently. I have reached out to the avionics shop that did the most recent work (GTN 650 and CGR 30P) for schematics when they did these installs in 2013 and 2014.
  • This is a 12v serial # 65 airplane
  • The airspeed safety switch has been tested and is operating properly

I have made copies of relevant sections of the electrical schematic and traced everything. The shop will get that in the morning. 

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Update: Sure enough, the radio master relay is broken and we're getting a replacement. Gear is still inop and tracing wires to see if there's a bad connection that might also have caused the radio master relay to quit, fry, etc...

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3 minutes ago, eft said:

Update: Sure enough, the radio master relay is broken and we're getting a replacement. Gear is still inop and tracing wires to see if there's a bad connection that might also have caused the radio master relay to quit, fry, etc...


MS for the win!   :)
 

relays are a drag… they fail without a lot of warning… after many years… and thousands of hours…

Some relays are tough to get lately…

 

Gear is equally complex… with relays and or position sensors… checking the input/output of each one should find the challenge…

Start with the switch… it will go to the first relays….

 

It might be time to check the pre-loads on the gear in case something has gotten out of order there…

 

PP thoughts only, not a mechanic…

Best regards,

-a-

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6 minutes ago, eft said:

Update: Sure enough, the radio master relay is broken and we're getting a replacement. Gear is still inop and tracing wires to see if there's a bad connection that might also have caused the radio master relay to quit, fry, etc...

Just so it’s clear ( @carusoam said it above), some of them are wired “fail safe” so that the loss of power to the avionics master causes the avionics relay to be powered on.  I’m just reiterating this so that you and your mechanic take a good look at how it’s wired before digging in there.

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The rest of the story: A single point of failure

A loose connection between the gear continuity circuit and the main bus bar (a screw had fallen out) was the root cause of ALL of these failures: Gear that would not extend or retract, annunciator lights that would not illuminate (except for the gear safe and unsafe), and the weirdness of an avionics master switch appearing to be defective (yes, we understand the fail safe nature of that circuit.) 

A hearty "hats off" to the crew and LASAR's new repair facility in Prineville, Oregon for sticking with this to find the solution, collaborating with the owner (me), my home base maintenance shop in Cincinnati, OH (Whitewater Aviation), and other experts. Whew! If you're ever looking for Mooney Service Center you should check these folks out! Prineville's a great place to visit, tons of "outdoorsy" things to see and do see, close to mountains, rivers, canyons, and Bend, Oregon's Deschutes River (anyone say fly fishing?) Bonus tip: Check out Wild Ride Brewing in Prineville (also locations in Redmond and Bend) which has some really great beer, a great family atmosphere, and resident food trucks with something for everyone.

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