Annunciator Lights - Press to Test not working

[tomslupilot]

I have a problem where I can't seem to get the annunciator lights to test with the push-to-test button.  I checked the bulbs and they're all good.  The gear lights work (up and down) respectively but none of the other 3 lights seem to work (overvoltage, Lo Vac, and Hi Vac).

When you press the push to test button should all lights come on (Gear Up, Gear Down, Overvoltage, Lo Vac, Hi Vac)?  

When you power the airplane on before starting the engine, does the Lo Vac normally light up?  (Mine does not)

Any ideas for troubleshooting?  Working with my mechanic as the airplane is in for the annual now.

Thanks,
Tom

[kortopates]

Review your POH as it has the details. But yes, when pushing the Push to Test buttom all lights except the Starter light will come on. The Starter light only comes on when the starter circuit is energized. If none come on with the Push to Test, then perhaps the button switch is no longer making a sound connection.

It always helps if you include your Model and year. What I said above may not apply to a vintage model.

[tomslupilot]

Its a 1969 Mooney M20C Ranger.

The book says "a press-to-test button at the top of the instrument panel illuminates all annunciator lights simulataneously."  I wasn't sure if that included the gear status lights (up/down) or just the warning annunciations (overvoltage/lo vac/hi vac).

I am also curious what triggers the lo vac light.  Would an airplane with the master switch on but engine off trigger a lo vac light?  Or is it only triggered when the vacuum system is operating (ie. engine running) and there is a malfunction.  The manual says "the Hi or LO vacuum annunciator light will illuminate if vacuum is above or below limits."  

Thanks,

Tom

 

[jax88]

I used to have random problems with my annunciators not working when tested.  I'd pull the bulb, reseat it, try again, and so on until I finally got them seated just right.  When I had my panel redone, the shop built a new face for the center stack, including the annunciators.  This new face provides a much more stable base for the bulbs and the switch.  Now I don't have any issues with testing the annunciators.  Perhaps having the portion of your panel that supports the annunciators rebuilt would eliminate your problem also?

[AlexR]

Greetings,

I have a 1970 M20C.  Yes, all lights (gear, voltage, and vac) should light up when you press the button and the master is on.  If your gear lights are working but the rest are not, check your breaker panel as gear warning lights are on a separate breaker than the 'annunciator lights.'  Could also be a lose connection behind the breaker.  Otherwise, you may have a bad or disconnected switch or something as simple as a bad ground.  If it is just the vac lights that are giving you problems (the low vac light should be on with the master on and the engine off), you can check the connections to the sensor.  mine is mounted to the back case of the attitude indicator.  It has four wires: power, ground, low, and high.  Hope this helps.

-A

[Hank]

Tom--

A couple of Octobers ago, about to start an evening IFR-training flight, I pushed that little button and thought I caught a brief whiff of smoke. The lights didn't come on, the radios didn't buzz, and the OBS needles didn't flicker. So I scrubbed the flight and had the mechanics check it out. The Push-to-Test button is attached to a small circuit board, along with all of your indicator lights and whatever panel lights you have since the panel light switch/dimmer goes there, too. They found a smoked component, but were not able to find a schematic; at great length I found a replacement board.

Made two flights while waiting, the second flight with no panel lights I had a total electrical failure while shooting a VOR-A below the clouds after completing an ILS in the clouds. Flew home slowly with approach flaps and gear hand-cranked the rest of the way down.

Don't mess with this, find out what's wrong. Someone earlier this year posted that they had found a schematic and were able to repair their board. Try the Search button, talk to folks, pull the board from your panel. Maybe it's just a loose connection.

[tomslupilot]

Hank- I realize this is above my paygrade and have my mechanic troubleshooting this issue.  We checked the obvious stuff today (switch, loose wire connections, bulbs).

On Monday, he is going to try and get the wiring schematic for the annunciator panel and compare it to the airplane.  

Alex- thanks for the suggestions, will pass them on.  The gear lights operate normally (show up and down when up or down).  Pushing the press-to-test button does nothing (no additonal lights come on).  We checked the ground today... when he removed the ground, the gear down light extinguished so that appears ok.  

Plan is to try and get a hold of the wiring schematic for the annunciator panel and go from there.

--Tom

[tomslupilot]

Does anyone have the wiring schematic for the annunciator circuit board on a 1969 M20C?

I looked in the Service and Maintenance manual and saw schematics showing the gear up/down wiring and the vacuum warning light wiring.  But I couldn't find the Annunciator Circuit Board wiring. 

There is something going on such that when the gear lights have ground (and working), the volatage/vacuum warning lights do not get power.  If you take away the ground to the gear lights, then the voltage/vacuum warning lights get power with the press-to-test button, but since there is no ground, it will not light up.

Its a complex plethora of wires so hoping a wiring diagram will help descramble the maze.

Thanks,
Tom

[DanM20C]

Tom,  I just sent you a PM.  I have the schematic for the board.  Do your panel lights work?

Dan

[tomslupilot]

Thanks Dan... Just what I was looking for!

--Tom

[SkyTrekker]

Hi Folks,

running into a related issue and wondering if I can get hands on the schematic.
 

-1970 M20E

-All lights operating normally

-But push to test does not illuminate any of them

-Rheostat operates all of the regular panel lights normally

Hoping for a schematic to troubleshoot the board and switch. 
 

Also open to any other suggestions. Image below. 

Many Thanks!

 

[carusoam]

On 11/16/2011 at 8:06 AM, DanM20C said:

Tom,  I just sent you a PM.  I have the schematic for the board.  Do your panel lights work?

 

Dan

 

Hey Dan,

Do you remember this?

Somebody else with possibly the same challenge...   ^^^^

Best regards,

-a-

[carusoam]

@SkyTrekker verify that you twisted the iris open... then push to test...

Sometimes the irises get closed, and people are not so familiar with them anymore....

Best regards,

-a-

[DanM20C]

Just now, carusoam said:

Hey Dan,

Do you remember this?

Somebody else with possibly the same challenge...   ^^^^

Best regards,

-a-

Indeed I do.  I’ve PMed the schematic to @SkyTrekker and will attach here for others.

 Cheers,

Dan

800275 Connections.pdf 800275 REV R.pdf

[carusoam]

MS is full up of amazing people...

Best regards,

-a-

[DanM20C]

7 minutes ago, carusoam said:

@SkyTrekker verify that you twisted the iris open... then push to test...

Sometimes the irises get closed, and people are not so familiar with them anymore....

Best regards,

-a-

1969 and newer they no longer used the irises.  They used a photo cell for automatic dimming.

 Cheers,

Dan

Edited May 21, 2020 by DanM20C

[SkyTrekker]

Thanks much, @carusoam and @DanM20C!

As was said, Mooneyspace is full of amazing people!

-Sia

[SkyTrekker]

@DanM20C,

Using the schematic you provided (thanks!) and a multimeter, it looks like my D14 diode is shot (not passing voltage in either direction). The other diodes I tested are passing voltage in one direction.

Does anyone know if this diode can be replaced with a standard 1N4001?

-Sia

[DanM20C]

2 hours ago, SkyTrekker said:

Does anyone know if this diode can be replaced with a standard 1N4001?

Yes. 

 Cheers,

Dan

[SkyTrekker]

For others who may run into this issue, in my case it was a bad diode. It was replaced with a 1N4001 and all is working perfectly now.

Thanks for all the help!

[carusoam]

Great follow-up, trekker!

Thanks for closing the loop.

Best regards,

-a-

[warren.huisman]

Anyone have the schematic for an 87 J model? I am having the same issue. Gear lights work but push to test does not.


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