piezo alarms in head liner, resistors and intermittent gear down light, Bitch'n Betty

[N231SM]

 

 

1980 M20K. We have 4 sonalerts in headliner: Stall, gear, Autopilot disconnect , and altitude preselect.

In confirming sonalerts faulty we discovered a few things I'd like to put out there for comment. Note that this info is based on info gathered with plane on jacks and swinging gear to test. I cannot run the engine due to engine work in progress. I am using a slow charger to keep battery charged during tests. I am new to the group and I may be covering too many topics here. So please let me know. 

After swinging gear a few times, the mechanical gear down light between the seats and the annunciator “gear down” lights on the original International Avionics annunciator A8/1000 do not always work. The mechanical floor indicator confirms it is down. I understand that the only way to check the gear is to make sure the floor indicator says it is down. But not having that light in the floor always work is strange. ALSO   when the test button is pushed on the annunciator, NO gear down light bulb. It seems to me those- the floor light and the annunciator light bulb-  are
 on the same circuit. When the lights fail, the annunciator is NOT getting power to the gear down pin. 

No gear down light on floor or panel annunciator
Gear is in fact down
annunciator gear bulb not illuminate when test button pressed
no current to annunciator pin

The next day I picked up where I left off and discovered that both gear down lights suddenly worked fine. That is after sitting on jacks all night. This has occurred on 2 occasions. Let the plane sit all night and they fix themselves. 

Do nothing except let plane sit all night and all is well:
Gear down light and annunciator light works
push to test button on annunciator works
power to annunciator is fine. 

I suspect that it is a sticky gear down limit switch or not enough battery power at the time of the test. When the lights fail, I have 12.2 volts. I recall an email which I cannot now find. The author mentioned a “tortuous” route of one of these circuits. If it turns out to be sticky switch, what is best way to clean/lubricate?  Can anyone else confirm that these lights are on the same circuit?
Anyone have any other advice?

Sonalerts 

There are resistors  in the hot wires that terminate in the headliner going to the sonalerts. They look to be original, strange little black bodies. Anyone know where to get those? (Zoom in on pic attached.)
    
Bitchn Betty

Also, has anyone installed the EI AV17 to work with a JPI EDM 701? Apparently the AV17 is triggered when a circuit (like oil pressure, cht, egt) is pulled to ground. 

Thanks. This is a fantastic site for Mooney owners.

 

[Vance Harral]

Welcome to the forums!

Assuming your Erie, Colorado location is correct, I'm literally in your back yard - also Erie CO (though our airplane is in Longmont).  Would enjoy getting together for lunch if you're inclined.  If it helps, our airplane goes in for annual tomorrow up at KLMO, and will be all opened up within a day or two.  You're welcome to come take a look while it's apart, though what you see on our 1976 M20F may or may not be relevant to your 1980 M20K.

Concur your problem may be bad limit switches.  These often clean up with a shot of spray-can contact cleaner.  But to really, properly diagnose electrical problems, you're going to want the electrical schematics for your airplane.  Ideally you'll find them in your Maintenance Manual (not the Parts Manual).  You want them for your particular make/model/serial number, because there have been minor variations in the way the warning systems are wired over the years.  This is especially true for the expected behavior of the push-to-test switch.  If someone here chimes in with info from another 1980 231, it will be good advice.  But advice from any other year or model is arguably a little suspect with respect to your particular airplane (ask me how I know...)

Those "resistors" on your sonalerts are almost certainly diodes, not resistors.  The part numbers for them will be found in your electrical schematics.

We have an EI AV-17 on our airplane as well.  It happens to be connected to an EI engine monitor rather than JPI, but the principles of operation are simple.  You're correct that it triggers voice alerts when a signal line is pulled to ground.  I can explain more about this when/if we get together.

Hope that helps, will look forward to meeting up if you're so inclined.  PM me for details.

 

[kortopates]

3 hours ago, N231SM said:

I suspect that it is a sticky gear down limit switch or not enough battery power at the time of the test....

On the floor board bulb, suggest check the bulb to socket connection at the base of the socket by cleaning it up to make sure its not an intermittent connection. Can't be the gear down limit switch or the gear would not stop till the actuator breaker pops (from reaching the limit of a stop mounted at the gear motor). Since its stopping, the switch is working, but I suspect you have a poor connection with the floor bulb. 12V should be enough to power the bulb.

Edited February 5, 2018 by kortopates

[jackn]

Both of those bulbs, as well as the sonalert are on the gear warning circuit. There is a micro-switch on the throttle that is also on this circuit. I’d be curious if by pushing in the throttle would allow the lights to come on. 

Anyway, it’s probably the sonalert. It’s taking its time to energize at which point the voltage comes up high enough to light the bulbs. 

[N201MKTurbo]

I believe your funny looking resistors are actually diodes. Are they bullet shaped or do they have a white band on one end?

Check if the dim bulbs are affected by the NAV light switch. The bulbs are dimmed with the NAV lights on.

Edited February 6, 2018 by N201MKTurbo

[N231SM]

OK,

 

Thanks guys. I have the parts manual and the schematics from seller. 

Anyone know of the specs on the diods? Mooney- buy there? From the diagram I cannot make out the part numbers "21LOC47" ?

So I am hearing that if we are flying along and you notice the gear is down, but no lights, the original engineers are trying to tell you that something is wrong in that circuit and it could be anywhere in that circuit: Throttle switch?, sonalert, diod, gear down limit, annunciation bulb. That makes sense. 

I am leaning towards the diod/bad piezo theory. I have a few on the way. Thanks for that info. and will keep you all informed. 

 

In 24-36-00 - LANDING GEAR CIRCUITS 1. Limit switches and relays operate the landing gear actuator, a 12 volt DC (25-0001 thru 25-0999) (24 volt for 25-1000 thru 25-TBA) reversible motor assembly. A landing gear air pressure safety switch, actuated by pitot air pressure, prevents landing gear retraction until a safe flying speed is attained. The landing gear control switch operates the actuator motor through the safety switch and relays. When the landing gear control switch is up and a safe flying speed has been attained, the safety switch closes to activate control relay, starting the actuator. As the gear reaches the up and locked position, a mechanical stop opens the up limit switch and the actuator stops. When the landing gear control switch is placed in the down position, the gear motor down-relay closes and the actuator starts. When the gear reaches the down-and-locked position, the mechanical stop opens the down limit switch and actuator stops. The gear-up limit switch controls the landing gear un-safe light. The red light comes on when gear is in transit. The green light comes on when the gear reaches down-and-locked position; the gear-down limit switch controls the green gear-down light....."

 

From what I gather, the throttle switch works with hMP, of which I have none, as my engine is out for rebuild. 

[kortopates]

12 minutes ago, N231SM said:

OK,

 

Thanks guys. I have the parts manual and the schematics from seller. 

Anyone know of the specs on the diods? Mooney- buy there? From the diagram I cannot make out the part numbers "21LOC47" ?

So I am hearing that if we are flying along and you notice the gear is down, but no lights, the original engineers are trying to tell you that something is wrong in that circuit and it could be anywhere in that circuit: Throttle switch?, sonalert, diod, gear down limit, annunciation bulb. That makes sense. 

I am leaning towards the diod/bad piezo theory. I have a few on the way. Thanks for that info. and will keep you all informed. 

 

In 24-36-00 - LANDING GEAR CIRCUITS 1. Limit switches and relays operate the landing gear actuator, a 12 volt DC (25-0001 thru 25-0999) (24 volt for 25-1000 thru 25-TBA) reversible motor assembly. A landing gear air pressure safety switch, actuated by pitot air pressure, prevents landing gear retraction until a safe flying speed is attained. The landing gear control switch operates the actuator motor through the safety switch and relays. When the landing gear control switch is up and a safe flying speed has been attained, the safety switch closes to activate control relay, starting the actuator. As the gear reaches the up and locked position, a mechanical stop opens the up limit switch and the actuator stops. When the landing gear control switch is placed in the down position, the gear motor down-relay closes and the actuator starts. When the gear reaches the down-and-locked position, the mechanical stop opens the down limit switch and actuator stops. The gear-up limit switch controls the landing gear un-safe light. The red light comes on when gear is in transit. The green light comes on when the gear reaches down-and-locked position; the gear-down limit switch controls the green gear-down light....."

 

From what I gather, the throttle switch works with hMP, of which I have none, as my engine is out for rebuild. 

From memory there is a good trouble shooting section on this in the service manual in addition to what you copied above.

As described above, there are many warning devices that come into play, but at only certain times, i.e. Gear UP, or Gear Down or Gear in transit.  

Following the schematic will show the exact circuit when the Gear is Down (gear down limit switch closed)  to illuminate the green lights, but recognize the MAP throttle switch and sonalert are only in the circuit when the gear is UP limit switch is closed and thus should be immaterial for when the gear is down. So is the airspeed switch, until you move the gear switch to UP.  So I'd bet its got to be in the circuit with the gear down limit switch closed (since your gear motor stops by the limit switch) - but referring to the schematic will ensure you don't miss anything. 

[Vance Harral]

1 hour ago, N231SM said:

From what I gather, the throttle switch works with hMP, of which I have none, as my engine is out for rebuild. 

In all the models I'm familiar with, the switch in question is mechanically controlled by the position of the throttle knob.  People talk about it being activated at a certain MP setting, but there's nothing that actually measures MP.  It would be more accurate to say it activates when the throttle is within about 1" of the stop.  You don't need to have the engine installed to activate it.

[KB4]

On 2/6/2018 at 2:54 PM, Vance Harral said:

In all the models I'm familiar with, the switch in question is mechanically controlled by the position of the throttle knob.  People talk about it being activated at a certain MP setting, but there's nothing that actually measures MP.  It would be more accurate to say it activates when the throttle is within about 1" of the stop.  You don't need to have the engine installed to activate it.

My POH says should activate at 12in, you want it adjusted to the manifold correctly, otherwise you could be listening to an annoying horn during a descent, and worse the buzzer looses its effect of smacking you in the face and asking "Is the gear down?"

 

 

[Gagarin]

During left base to final the stall warning may be mistaken by the gear warning that may induce to a gear up landing. To avoid this possibility I installed a Voice Alert warning alarm. Very effective specially for those on Medicare but it is not covered by Medicare.

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