Gear Up Alarm fail at annual

[TargetDriver]

So just finished my annual and  everything was fine...or so I thought, except for when the IA asked to hear the gear up alarm when it was on the jacks. Nada, crickets.  This was my first annual since buying the plane two years ago. (spent a year in Afghanistan).  I literally said "don't think it has one, never heard it and the prebuy and annual at purchase never demonstrated it to me"  He wasn't amused.  Bad me.  So much for an easy annual.

So we tested just the gear up buzzer and it didn't work, only clicked lightly. Thought it was bad until an electrical engineer that has a plane on the field happened by. He checked the buzzer with a 12v power source and it buzzed fine...thats when he showed us that the Mallory buzzer has polarity. turns out it was installed in the plane backwards at some point. figured that fixed it. reinstalled it and the thing wouldn't shut off !  He also crawls under the panel and checks the throttle limit switch (must be all the way out -at idle-ish) to make the micro switch.  He finds that it's allowing power to pass even when its made - the throttle is not at idle.  Bad micro switch.  So I replace the micro switch. Back to the jacks today for the sign off when the buzzer stops after pushing in the throttle, with the gear unlocked or up.  Nope. Still buzzing.

The only logical path for power now to be feeding the buzzer when it shouldn't be is maybe one of the limit switches, up or down.... or possibly our electrical engineer friend also suggested maybe it could be one or both of the two diodes at the buzzer power wires (thgere's 3 wires crimped into the same terminal. (per factory schematics)   Perhaps if one of those was bad?  However, when we do the gear swing, they work perfectly so that to me kills the bad up or down limit switch possibility.  A side note - when the Gear Cont breaker is pulled the buzzer stops, but so does the gear. Kinda need that.

Has anyone ever had this issue, warning buzzers going bad or similar where the buzzer will not shut off?   Strange I know.

The fact that the gear up warning buzzer was possibly wired backwards might have been intentional to just stop it from going off, not sure.  I bought a new multimeter tester with a diode testing feature. Will test those tomorrow morning. Went to electronics store to find a diode in case I need to soldier in new ones... doing tha tjob is a no brainer...figuring out which diode to buy as a non-electronics guy...impossible.

Suggestions ?     ...and no we don't have an aircraft type electrician on or around the field.

Thanks guys ! 

 

 

[TargetDriver]

Sorry, totally forgot to add the important stuff.  1980 K model. Piezo alarms looked to be original - Mallory Sonalerts.   # -0345.  If I forgot something important, dont hesitate to ping me.

[carusoam]

Does your POH wiring diagram have enough detail to include the sonalerts?

Do you have access to a maintenance manual for the complete wiring diagrams?

The wiring probably goes back to the 60s for this...  

• power
• gear position switch
• throttle position switch
• sonalert
• ground

If the gear is up, and throttle is out, the power should be flowing to the sonalert...

Green light off, throttle switch in the divot, sonalert blaring... 

Make sure you have the right sonalert... the other one is the stall horn...

is the throttle switch (wheel) finding the divot in the throttle shaft?

I’m not sure about the diodes...

My experience comes from the manual gear in the C.  The gear’s green light switch is mounted in the hole/receiver for the Jbar...

A low throttle descent with the gear up, leaves the sonalert blaring... or your finger stuck in a hole... 

Sonalerts have been known to croak after 50years... If you are in there cleaning all the connections, it might be wise to replace with a new sonalert...

See if any of this makes sense... PP thoughts only, not a mechanic... Welcome back!

Best regards,

-a-

[TargetDriver]

Car-,

Thanks for reply. Yes I have the maintenance manual (on my laptop) and it shows the complete electrical schematics.  It does show the gear  warning horn (but doesn't call out Sonalert) Both the gear up and the stall warning buzzers are Sonalerts. Both have two terminal tabs ( a + and a - ) with small screws. The gear warning Sonalert has 3 wires coming that are factory crimped to a single ring terminal. On the positive side there is a diode on two of the wires, one facing toward the buzzer, the other facing away.  (I was told diodes are basically one-way "valves") so it looks like the power comes in, goes through and then out of the buzzer, with the diodes preventing power from feeding backwards.

I replaced the micro switch on the back side of the throttle, just behide the panel. It was a bear, but it did test as it should, which the original one tested bad.

Yes, as I understand it, with the gear not down and locked, and when the throttle cable is (in my case) all the way out, at idle, the alarm should sound. In my case, now it does, BUT...when you push the throttle in some, past the detent that the micro switch settles down into, the alarm should stop, but it doesn't - it keeps buzzing. 

I did test the diodes earlier today by first watching a couple videos on simple diode testing ... neither one "passed" or did what they were supposed to according to multiple testing videos.  Several guys said its rare for diodes to ever go bad, little alone two of them, unless there was a major power surge. 

 

[carusoam]

TD...

Diodes are simple oneway valves for electrons...

An easy way to break them is to connect them backwards... they overheat and melt pretty quickly...   hmmmmm....?

a common application of diodes is turning AC power from a magneto into DC power... sort of... works good enough for lawntractors...

I got the wrong battery for my lawn tractor (tug)... the terminals were reversed... being in a rush and really smart... I connected the battery without checking all of the details... the diode that controlled the flow of electrons to charge the battery began smoking...

That set my tug project back another year...

Best regards,

-a-

[Andy95W]

1 hour ago, TargetDriver said:

  ...and no we don't have an aircraft type electrician on or around the field.

There really isn't any such thing as "an aircraft type electrician".  There are A&Ps that are good at wiring and there are A&Ps that aren't.

Its really pretty simple: your buzzer is getting power and ground at times when it shouldn't.  Using the schematics, trace from the ground backwards through the circuit until you get to a voltage source.  On the diodes, current only flows in one direction, so the electrons will flow from the ground through the diode in the direction that the triangle points.  Check each piece of wire and switch until you find your culprit.

My guess is that if it isn't a diode, then you have a chafed wire that is making its own ground.

[TargetDriver]

Andy,  Thanks for great info.  I have some good A&P's at our small little airport, but as you've said, they're not the wiring guru's...and I'm the guy that momentarily electrocuted himself changing a hot water heater... 220v hurts and suuuucks.  ha   I can build the plane, just dont know diddly about those electrons.

Agreed, its getting power when it shouldn't.  The chaffed wire idea scares the crap out of me. Seems so daunting to find which one it is as they all disappear into the wiring abyss.

So, I have a question. Are you talking about a power wire thats grounding/chaffed or a ground side wire? Doesn't make sense to me that a ground side wire would be a problem grounding somewhere else.

I've high lighted the headliner part of the schematic that shows the gear warning horn.

 

 

[PTK]

6 hours ago, carusoam said:

...Diodes are simple oneway valves for electrons...

And they should really be called uni-odes! 

[Marauder]

Car-,
Thanks for reply. Yes I have the maintenance manual (on my laptop) and it shows the complete electrical schematics.  It does show the gear  warning horn (but doesn't call out Sonalert) Both the gear up and the stall warning buzzers are Sonalerts. Both have two terminal tabs ( a + and a - ) with small screws. The gear warning Sonalert has 3 wires coming that are factory crimped to a single ring terminal. On the positive side there is a diode on two of the wires, one facing toward the buzzer, the other facing away.  (I was told diodes are basically one-way "valves") so it looks like the power comes in, goes through and then out of the buzzer, with the diodes preventing power from feeding backwards.
I replaced the micro switch on the back side of the throttle, just behide the panel. It was a bear, but it did test as it should, which the original one tested bad.
Yes, as I understand it, with the gear not down and locked, and when the throttle cable is (in my case) all the way out, at idle, the alarm should sound. In my case, now it does, BUT...when you push the throttle in some, past the detent that the micro switch settles down into, the alarm should stop, but it doesn't - it keeps buzzing. 
I did test the diodes earlier today by first watching a couple videos on simple diode testing ... neither one "passed" or did what they were supposed to according to multiple testing videos.  Several guys said its rare for diodes to ever go bad, little alone two of them, unless there was a major power surge. 
 

I have had issues with those diodes. They can go bad. Also check the Amp connectors for any evidence of corrosion being in them (from condensation or water getting into them.).


Sent from my iPhone using Tapatalk Pro

[Andy95W]

8 hours ago, TargetDriver said:

Andy,  Thanks for great info.  I have some good A&P's at our small little airport, but as you've said, they're not the wiring guru's...and I'm the guy that momentarily electrocuted himself changing a hot water heater... 220v hurts and suuuucks.  ha   I can build the plane, just dont know diddly about those electrons.

Agreed, its getting power when it shouldn't.  The chaffed wire idea scares the crap out of me. Seems so daunting to find which one it is as they all disappear into the wiring abyss.

So, I have a question. Are you talking about a power wire thats grounding/chaffed or a ground side wire? Doesn't make sense to me that a ground side wire would be a problem grounding somewhere else.

I've high lighted the headliner part of the schematic that shows the gear warning horn.

 

 

After looking at your diagram, I agree it's not a chafed wire finding a ground.  Your ground is always on, so the switched side must be from  power.

[On older models (like mine), power is applied at one side of the horn and switches etc. give it a ground to activate.  Evidently newer airplanes were the opposite.]

I'm going to guess it is the diode 21WE05A, but if one's bad, the other is probably too.  

First I would isolate the throttle switch by disconnecting the end that supplies power to the horn.  Using your voltmeter, make sure the switch makes contact at an appropriate location as you move the throttle.  Though rare, I've seen bad new switches or ones that looked right but were installed slightly off so the switch activated incorrectly.

If the throttle switch works correctly, then either a different switch is supplying power when it shouldn't or a diode is bad and allowing current to flow backwards when it shouldn't.  Either way, it's a tedious process of working step be step until you find the culprit- but you will, in the end.

Good luck, keep us posted.

[ShuRugal]

9 hours ago, TargetDriver said:

Andy,  Thanks for great info.  I have some good A&P's at our small little airport, but as you've said, they're not the wiring guru's...and I'm the guy that momentarily electrocuted himself changing a hot water heater... 220v hurts and suuuucks.  ha   I can build the plane, just dont know diddly about those electrons.

Agreed, its getting power when it shouldn't.  The chaffed wire idea scares the crap out of me. Seems so daunting to find which one it is as they all disappear into the wiring abyss.

So, I have a question. Are you talking about a power wire thats grounding/chaffed or a ground side wire? Doesn't make sense to me that a ground side wire would be a problem grounding somewhere else.

I've high lighted the headliner part of the schematic that shows the gear warning horn.

 

 

Like Andy said, Looks like the horn is grounded along 3 different paths (21LC14F20, 21LC25F20, and 21WE15G20), with no switch on ground

Looking at this Diagram, I dont see the switches on the + legs (must be on another page - find them please?) but here is what i think is going on:

 

21WE31D22 and 21WE14D22 are both capable of energizing the horn if + voltage is applied to the other end. 31D22 looks like it is intended to be used with an AC supply to give a half-wave rectification, which would be adequate to drive a buzzer.  21WE16D22 appears to be set up so that it can ground out the + terminal to kill the buzzer - the way that diode is oriented, applying + voltage to that lead will not energize the horn.

 

Without seeing where the other end of those 3 leads go, it's hard to say for certain, but if my guess is correct, the switch logic should look like this:

(21WE31D22 OR 21WE14D22 closed) AND (21WE16D22 open) == Buzzer ON

(21WE31D22 AND 21WE14D22 OPEN) OR (21WE16D22 CLOSED) == Buzzer OFF

 

If you can provide the portions of the wiring diagram showing where those leads go after passing through the connector at the lower right, we can confirm if this is correct, and I can tell you what the circuit is doing.

 

[EricJ]

4 hours ago, PTK said:

And they should really be called uni-odes! 

Diodes are two-terminal devices (i.e., two electrical connections) instead of something like a typical transistor, which is a triode.    The naming convention is left over from early days of electrical device implementation, including vacuum tubes.   Eventually the name became attached to the function rather than the device configuration.

[Marauder]

1 hour ago, ShuRugal said:

Like Andy said, Looks like the horn is grounded along 3 different paths (21LC14F20, 21LC25F20, and 21WE15G20), with no switch on ground

Looking at this Diagram, I dont see the switches on the + legs (must be on another page - find them please?) but here is what i think is going on:

 

21WE31D22 and 21WE14D22 are both capable of energizing the horn if + voltage is applied to the other end. 31D22 looks like it is intended to be used with an AC supply to give a half-wave rectification, which would be adequate to drive a buzzer.  21WE16D22 appears to be set up so that it can ground out the + terminal to kill the buzzer - the way that diode is oriented, applying + voltage to that lead will not energize the horn.

 

Without seeing where the other end of those 3 leads go, it's hard to say for certain, but if my guess is correct, the switch logic should look like this:

(21WE31D22 OR 21WE14D22 closed) AND (21WE16D22 open) == Buzzer ON

(21WE31D22 AND 21WE14D22 OPEN) OR (21WE16D22 CLOSED) == Buzzer OFF

 

If you can provide the portions of the wiring diagram showing where those leads go after passing through the connector at the lower right, we can confirm if this is correct, and I can tell you what the circuit is doing.

 

When you say the buzzer is "on" is it chiming at the full intensity or more of a shadow of the full alarm? The reason I am asking is that is what was setting off my stall warning. Moisture had gotten into one of the Amp connectors and it allowed current to flow to the Sonalert anytime the master was on. Instead of getting a full chime, it sounded like a weak version.

The diodes are still high on my list.

[jackn]

I drew a simplified schematic of this circuit just to understand what is going on. It’s at my hanger right now though. As I remember, there are 2 switches that control the buzzer. One is the throttle micro-switch, the other is from the airspeed switch. 

Maybe I misread, but you have the plane up on jacks with the gear up. The buzzer will sound because the airspeed switch is closed. This is regardless of the throttle position. 

[TargetDriver]

2 hours ago, ShuRugal said:

Like Andy said, Looks like the horn is grounded along 3 different paths (21LC14F20, 21LC25F20, and 21WE15G20), with no switch on ground

Looking at this Diagram, I dont see the switches on the + legs (must be on another page - find them please?) but here is what i think is going on: 

 

21WE31D22 and 21WE14D22 are both capable of energizing the horn if + voltage is applied to the other end. 31D22 looks like it is intended to be used with an AC supply to give a half-wave rectification, which would be adequate to drive a buzzer.  21WE16D22 appears to be set up so that it can ground out the + terminal to kill the buzzer - the way that diode is oriented, applying + voltage to that lead will not energize the horn. 

 

Without seeing where the other end of those 3 leads go, it's hard to say for certain, but if my guess is correct, the switch logic should look like this:

(21WE31D22 OR 21WE14D22 closed) AND (21WE16D22 open) == Buzzer ON

(21WE31D22 AND 21WE14D22 OPEN) OR (21WE16D22 CLOSED) == Buzzer OFF

 

If you can provide the portions of the wiring diagram showing where those leads go after passing through the connector at the lower right, we can confirm if this is correct, and I can tell you what the circuit is doing.

Shu,  Wow, thank you for all that. I am in way over my head but I'll keep pressing on with your guys help.  I've attached shots of the two switches from the + side of the buzzer.  21WE31D22 goes to the Gear Safety Switch. 21WE16D22 goes to a Gear Up Limit Switch.   I traced the lines as best I could with red pencil.  Hope this helps. 

I bought a multimeter to test the diodes. I'm not getting any of the readings shown on any of the You Tube videos testing diodes.  One suggestion was that I disconnect (read- cut) one wire of a diode to be able to test it properly (with no possible voltage going to it) .  Gonna wait to do that until it looks like it's a diode.

[TargetDriver]

11 minutes ago, jackn said:

I drew a simplified schematic of this circuit just to understand what is going on. It’s at my hanger right now though. As I remember, there are 2 switches that control the buzzer. One is the throttle micro-switch, the other is from the airspeed switch. 

Maybe I misread, but you have the plane up on jacks with the gear up. The buzzer will sound because the airspeed switch is closed. This is regardless of the throttle position. 

Jack, thank you !   I read in the maintenance manual about the airspeed switch (I presume it's the one just under the left leading edge that looks like a small paddle hanging in the airstream)  but I haven't seen that anywhere in the full schematic.  

Yes we had the plane up on stands.  The buzzer should sound when the gear is in any condition other than "down and locked" AND the throttle is at idle ( throttle micro switch is allowed to fall open just at the end of the cable housing).  It did buzz like this, BUT it should have stopped when the throttle was pushed in some, which closed the micro switch...but it dfidn't. It just keeps buzzing.  

So are you saying that the airspeed switch needs to be held back like its flying so the horn will stop? 

Thank you all for your continued help !!!  You guys rock.

[jackn]

The airspeed switch is attached to the back of the airspeed indicator. There is a procedure in the maintenance manual to check it. Essentially, you put a piece of surgical tubing on the pitot tube and roll it closed until the switch opens. I think it opens when The asi gets to about 65kts. 

[ShuRugal]

1 hour ago, TargetDriver said:

Shu,  Wow, thank you for all that. I am in way over my head but I'll keep pressing on with your guys help.  I've attached shots of the two switches from the + side of the buzzer.  21WE31D22 goes to the Gear Safety Switch. 21WE16D22 goes to a Gear Up Limit Switch.   I traced the lines as best I could with red pencil.  Hope this helps. 

I bought a multimeter to test the diodes. I'm not getting any of the readings shown on any of the You Tube videos testing diodes.  One suggestion was that I disconnect (read- cut) one wire of a diode to be able to test it properly (with no possible voltage going to it) .  Gonna wait to do that until it looks like it's a diode.

Okay, looks like the diode going FROM the horn leads to the gear up limit switch - I would guess that is a normally-closed switch, which opens when gear is retracted.  I don't see where it goes from that switch, but i would expect ground.  The Diode TO the horn is fed from the gear safety switch, which should be the one on the back of your ASI.  This should also be a normally-closed switch, which is opened by sufficient pressure to indicate safe flying speed.

As jack stated, the gear-safety switch is probably gonna be the culprit here.  You can test it with surgical tubing as he suggested, or if your A&P has a pitot/static tester, it can be tested that way as well.  Just run the pitot pressure up until the horn stops, and note the indicated speed.

 

[carusoam]

The K is one of the most complex airframes Mooney ever built...  

Since the airspeed switch is a likely concern...

See if the by-pass switch isn’t accidently involved in this crime, somehow... (see if you can activate it normally, while safely on jacks, clearly communicating with your partner...)

Notice all the part numbers have a name next to them? This is helpful to know what they actually are... handwritten in neat handwriting....

• Up limit switch
• up relay
• gear horn 
• gear safety switch (airspeed/Pitot Pressure)
• Overide switch (push button on panel)

 

this possibly interesting part of the drawing seems like it got lopped off... some gear logic is covered here...

• 14v essential
• gear down High 
• gear down 
• (Gear up)?
• (ground)?

 

Just keep in mind, while probing switches, you may activate some motion while not expecting it... the motion may continue even after you remove whatever action started it...

Keep all human body parts away from moving machinery parts... 

When done... make sure the similar stall warning horn system is still working. 

PP thoughts only, not trained in Mooney mechanicals....

Best regards,

-a-

[Oldguy]

2 hours ago, TargetDriver said:

Jack, thank you !   I read in the maintenance manual about the airspeed switch (I presume it's the one just under the left leading edge that looks like a small paddle hanging in the airstream)  but I haven't seen that anywhere in the full schematic.  

Yes we had the plane up on stands.  The buzzer should sound when the gear is in any condition other than "down and locked" AND the throttle is at idle ( throttle micro switch is allowed to fall open just at the end of the cable housing).  It did buzz like this, BUT it should have stopped when the throttle was pushed in some, which closed the micro switch...but it dfidn't. It just keeps buzzing.  

So are you saying that the airspeed switch needs to be held back like its flying so the horn will stop? 

That should be your stall warning vane. Holding it up with the Master on should sound the stall warning horn/buzzer in the cabin.

[TargetDriver]

So a daily update ...

Been at it all day. removed belly panels-checked up and down limit switches for electrical function and installation and adjustment. All fine.

Pulled right breaker panel (out about 3 in). Checked for bad connections/loose/broken wires. All fine  Tested Gear Cont, Gear Warn breakers. all fine.

Checked airspeed safety switch in right wing leading edge (its just inboard of the stall warning switch). The switch itself checked good but but never showed current running through it in any condition.  Tried it taped back to simulate airflow (switch made by pressure from the small paddle that would be in the air stream). No difference.

Checked Sonalert horn again for proper function. Works as expected.

Cannot get to the Over Ride gear bypass switch next to annunciator panel without removing front main panel.

Found one diode,  inline on the -16D22 going to the Up limit Switch that tested bad (slightly passing) after we de-soldered one end. Bought another dioide to match it, installed-no change to horn operating while the throttle was advanced off of idle.  HOWEVER...

Throttle at idle, I just ran the gear up, horn sounding, pushed throttle in halfway, still sounding (should have stopped off idle with the throttle) so I pulled the Gear Cont breaker to shut it up...then by chance, I pulled the throttle back to idle, not thinking - the Horn Sounded like it should !   So, with the gear Cont breaker out the horn works as it should, but of course the gear action stops.

I'm going to dive back into the schematic and start at the Gear Cont Breaker.   If this means anything to you guys, I'm all ears !!  and have a endless supply of gratitude!

 

[carusoam]

No, no, no.... 

Stall warning switch is not the airspeed safety switch...

• One warns of an impending stall.
• The other is part of the gear retraction system... it safely keeps the gear from retracting before the plane reaches flying speed...

The stall warning vane is on the leading edge of the pilot side wing...

The airspeed safety switch is a diaphragm switch sensing and acting on air pressure in the Pitot system. Often found on the back of the ASI... 

I noticed some people are trying to clear this up for you.

Best regards,

-a-

[TargetDriver]

Airspeed switch- I got all the way under the panel and there is nothing attached to or coming off of the back of the airspeed indicator. It's back its basically flat with a small black plastic boss in the center with some wires that are heat shrinked together, possibly 3 or 4 wires.  Nothing to put a nipple or rubber surgical hose on to.

I have attached a pic of what I believe is the airspeed safety switch.  MS has rotated the pic 90 deg. Sorry.

[TargetDriver]

Car...  Yes, true.  I just posted a pic (it posted sideways)  of what I believe is this planes version of the airspeed saftey switch.  I just checked the back of the airspeed indicator and there's absolutely nothing back there. Its flat with no ports, fittings or nipples.

Yes, the Stall Warning "switch/Sensor" is about 12 in outboard of the airspeed safety switch.  We did test the stall warning switch by holding it up with the Master on and it sounds as expected when held up, as would be in a high alpha disturbed stall condition.

 

[carusoam]

That’s unique...

See if that shows up in the logs anywhere... somebody put a fair amount of effort in to mount that switch...

Those donuts are looking pretty fresh.... 

Best regards,

-a-