M20J - All Annunciators Illuminated

[WheelPantsOff]

Good evening,

I have a discrepancy where all of my annunciators are illuminated when power is applied to the airplane - battery or ground power - regardless of the position/condition of the system it is indicating.  It recently had some extensive behind the panel work with a new GPS and transponder and I am half a world away from my wiring diagrams for the foreseeable future.  In the interest of helping the shop out, any initial ideas or starting points to help them along?

Thanks in advance!

[LANCECASPER]

6 minutes ago, WheelPantsOff said:

Good evening,

I have a discrepancy where all of my annunciators are illuminated when power is applied to the airplane - battery or ground power - regardless of the position/condition of the system it is indicating.  It recently had some extensive behind the panel work with a new GPS and transponder and I am half a world away from my wiring diagrams for the foreseeable future.  In the interest of helping the shop out, any initial ideas or starting points to help them along?

Thanks in advance!

Is the "TEST" switch stuck on?

[WheelPantsOff]

3 hours ago, LANCECASPER said:

Is the "TEST" switch stuck on?

He tested the momentary push to test switch and it passed.  Not just that the button rebounded/sprung back to the 'off' position but also that the switch was working with a meter.  I took his word for it, but if there's a test job card or wiring diagram that I could send him to be sure, I would certainly appreciate it.

Thank you!

[PT20J]

Look in the service and maintenance manual section 24-39.

You might also contact international Avionics Inc that made the panels for Mooney. They still repair them. If it’s not the test switch itself, then it’s probably some internal failure of the test circuit.

[ArtVandelay]

The J has a auto dimming circuit for the landing gear down annunciation, it’s tied to the nav lights, was there any chance this was altered?

[WheelPantsOff]

The problem has been solved and once I get a time to talk with the vendor, I'll post the results here in case anyone else comes across a similar problem.

[WheelPantsOff]

During the avionics install, there were some mis-routed CB wires and a pin on the annunciator panel which is not used but was connected with a wire leading to a CB.  Once the vendor started pulling CBs, when they hit one of them, the annunciator panel lights extinguished to what should have be in an engine-off, power on state.  They're wrapping it up and hopefully it is ready for test flight and delivery shortly.

[PT20J]

Interesting. My M20J service manual doesn’t have a complete schematic of the annunciator panel, but piecing what is there with the aircraft schematic, it appears that the test button applies 28v through a diode to pin 4 of the annunciator connector as an external test output. The diode should isolate it to prevent power applied there from illuminating the bulbs in the annunciator. Maybe the diode is shorted, or the schematic is wrong. Just to be safe, I would have the shop verify all the functions of the annunciator.

[WheelPantsOff]

Almost all of the annunciator functions were tested correct but I am having an issue with the Right Fuel Low annunciator.  During test, it is not illuminating, and the fuel was run down to almost empty on that tank so it's not illuminating under a known condition either.  Swapped bulbs and it's not the bulb.  I'm still away and curious where I can send have the tech look.

[Marc_B]

I ran into some annunciator issues with an install, but this was with new circuitry and it was some miss mapped pins.  Long story short, the Test + and Test - pins on the back of the annunciator are for bench testing only.  They should not be connected to power or ground.  The electrical schematic for your aircraft will have the pin out for your unit.  This doesn't necessarily match another Mooney model or even same Mooney but different SN range.  So you need to pull the schematic for your SN.

On 2/29/2024 at 8:18 AM, PT20J said:

it appears that the test button applies 28v through a diode to pin 4 of the annunciator connector as an external test output.

You'll notice on my schematic below that pins 4 and 14 aren't connected to anything in the ship and it should stay that way.  If power was connected here and it fried the test circuit then you might need to send it back to IAI if you still have problems with the test button not working or working erratically.  The test button should be just a momentary switch to connect bus voltage though the lights to validate that they all illuminate.

Most of the circuitry isn't spelled out in the MSM as it only discusses the more complicated circuits.  Quite a few of the indications are what Mooney called a Typical Positive Apply.  Basically it just illuminated when aircraft voltage applied (in my case +28VDC) to the pin.  This applies to many of them like boost pump, speed brake, stand by vacuum, prop deice, etc.

The fuel comparator circuits are the more complex inside the annunciator and you'll find a description of those in the MSM.  If you're continuing to have issues I'd reach out to International Avionics, Inc in Richardson, TX.  The person I worked with was Kenneth Snowden; main number 972/417-2820.

 

Annunciator_MooneyServiceManual.pdf

Edited March 10, 2024 by Marc_B
added MSM pages RE annunciator circuits

[FADEC]

I am intermittently have the same issue all of the lights illuminate on the annunciator panel but only when the gear are down, then the gear are up all lights are out and the test switch works as advertised.  It’s a very intermittent issue and is proving hard to troubleshoot.

 

 

Andy

[PT20J]

12 hours ago, FADEC said:

I am intermittently have the same issue all of the lights illuminate on the annunciator panel but only when the gear are down, then the gear are up all lights are out and the test switch works as advertised.  It’s a very intermittent issue and is proving hard to troubleshoot.

 

 

Andy

The TEST+ circuit is what illuminates all the lamps when energized by the TEST button. There is a diode that isolates TEST+ from the GEAR DN light. If this diode is shorted, it will cause the gear down indication to energize the TEST+ circuit.

[FADEC]

7 hours ago, PT20J said:

The TEST+ circuit is what illuminates all the lamps when energized by the TEST button. There is a diode that isolates TEST+ from the GEAR DN light. If this diode is shorted, it will cause the gear down indication to energize the TEST+ circuit.

I am going to assume that diode is inside the annunciation panel, is that something that should be fixable by an standard avionics shop, or someplace more specialized. Thanks for the reply and info.

 

Andy

[PT20J]

4 minutes ago, FADEC said:

I am going to assume that diode is inside the annunciation panel, is that something that should be fixable by an standard avionics shop, or someplace more specialized. Thanks for the reply and info.

 

Andy

Assuming that is the problem, the diode will be on a circuit board within the annunciator panel and if your avionics shop still does bench repairs it should be easy to replace it. As people with knowledge of repairing legacy avionics have been retiring, and more of the modern avionics is not easily field repairable, it's getting harder to find shops that will repair stuff -- most of the money these days is in sales and installations. 

IAI made the annunciators for Mooney. They are still in business and I might contact them about a repair. https://www.internationalavionics.com/

 

[FADEC]

22 minutes ago, PT20J said:

Assuming that is the problem, the diode will be on a circuit board within the annunciator panel and if your avionics shop still does bench repairs it should be easy to replace it. As people with knowledge of repairing legacy avionics have been retiring, and more of the modern avionics is not easily field repairable, it's getting harder to find shops that will repair stuff -- most of the money these days is in sales and installations. 

IAI made the annunciators for Mooney. They are still in business and I might contact them about a repair. https://www.internationalavionics.com/

 

Thank! Its frustrating that its so hit and miss.

 

Andy