"Gear CONT" CB Popping Occasionally.

[N9656G]

Hello, 

I have spent the last 48 hour's skimming though 455 pages of the J model service manual to no avail.

On 2 of the last 10 flights my "Gear CONT" 5A CB popped. I would assume this is for "Gear Control" AKA the actual panel mounted wheel style gear switch and override button. 

Only thing that has been different on these flights was letting a pilot rated passenger swing the gear both times this occurred. One was on retraction, the other time on extension. Can this be caused by not operating the switch quick enough? Where I usually pull it OUT and DOWN or OUT and UP perhaps my passenger did not do that quickly enough and the extra time in cycle caused a spike in voltage enough to pop the Gear CONT CB. 

Only other thing I can think was before this last occurrence, I also was showing this pilot rated passenger after startup where the manual extension was and how it is operated. (Mine is pull start version behind trim wheel with safety latch) I obviously didn't operate it on the ground, but I did show them how the safety latch works and reveals the manual extension handle. Can this trip the Gear Cont CB? 

Regardless, each time it has occurred a simple reset of the CB "fixed" the issue. 

What would you do?

Clean contacts on gear control wiring?

Order a new 5A CB?

Wait for it to happen a few more times?

Gear is cycling at normal speed and sounds and feels normal. 

[PT20J]

The document you want is the schematic for your airplane which is part 2 of the service manual.

The only way that a normally operating emergency gear extension system will blow a breaker is if you engage the handle fully and then try to operate the gear. The engagement will prevent the motor from turning which will cause the Gear Actuator breaker to pop -- not the Gear Control breaker.

The Gear Control circuit supplies power through the various switches to the gear up and gear down relays which in turn operate the motor. So, the only load on this circuit is the relay coils.

Assuming the wiring is sound, the usual suspect would be a gear relay or the flyback diode across the coil. However, since you experienced the problem during both extension and retraction, it is unlikely a relay because it would be improbable for both to fail simultaneously. So, it would have to be something common to both circuits, and probably the most likely component is the circuit breaker.

Circuit breakers are pretty reliable. However, they really should be manually exercised occasionally or oxidation can build up in the contacts which can cause internal heating and lower their trip point. I exercise all mine once or twice every annual.

If it were my airplane, I'd exercise the breaker a few times and see if it repeats before doing any additional troubleshooting.

Skip

 

[skykrawler]

Another M20K owner at my airport is having a similar problem.  "Gear Cont" breaker, intermittently popping the breaker.

We're going to dig in when he gets back from Florida.

[jetdriven]

It may be a weak circuit breaker to one of the pilots here spent four days, tearing his airplane all apart just to find out that the gear actuator breaker was weak and would trip when raising the gear. 
I suppose you could put a load on it on jacks and resist the motion of it and see if that’s enough to make it trip. 
 

Edited April 3 by jetdriven

[skykrawler]

Since the popping breaker is the 'Gear Control' the only thing pulling current on it is the up and down gear relays and maybe a light (not the actuator, which has its own breaker).   Plan to test the control breaker by putting a load on it with something about 60 watts power.

He called a Mooney service center and they suggested the up limit switch was causing the up relay to engage constantly.   But, this would cause the gear to run against the stop and also cause the 'Gear Act' breaker to pop.

It could be a diode going bad on the up relay that shorts intermittently.  That would splain it,  but only if it happens during retract - once on the limit switch power to the relay is removed.

Another symptom I heard described is: the gear is retracted and the breaker is popping.  The gear lever is moved to command gear down, the breaker is closed and remains closed, and the gear extends.

[ArtVandelay]

IIRC, not have the emergency gear red lever lock can also cause this.

[PT20J]

4 hours ago, ArtVandelay said:

IIRC, not have the emergency gear red lever lock can also cause this.

That jams the motor and will trip the gear actuator breaker.

[skykrawler]

Update on the M20K airplane with the popping "Gear Cont" circuit breaker.  On the flights immediately preceding this activity the circuit breaker had popped two or three times after retract.

The airplane was jacked and the belly #2 panel removed for access to the limit switches and relays.   All the the wiring was thoroughly examined including the left side cabin interior where the harness for the gear switches and relays come up (a pinch point) and going forward until it goes into the harness and is untraceable.   The circuit breaker area was examined for loose lugs and rouge loose screws.  The wiring through the gear safety switch was checked (a path for control voltage).
The gear was cycled >25 times (with the airspeed safety switch satisfied) and the CONT circuit breaker never popped.   Two halogen 37 watt bulbs were connected in parallel to the up relay coil input to increase the load on the  5 amp control breaker, the actuator breaker was pulled and the gear commanded to retract.   This powers the up relay and the lights continuously  - the CONT did not pop indicating the problem is not a weak circuit breaker or 'continuous relay on' load problem.   The up limit switch was cycled by hand many times each time turning the up relay off/on - no problems.   A short to ground from the relay coil input pops the breaker verifying the breaker will operate.
The up limit switch was replaced with a new switch and the gear operation (retract stop point) checked.  The lower gear door on the left (port) side was too tight and adjusted.  All the gear activity caused the wire to light bulb socket under the floor to fatigue break (a previous repair) - this was repaired with better strain relief.

The gear was probably cycled 40 times total on the jacks and the breaker never popped.  The airplane has since flown twice with 8 retract cycles with no popping of the circuit breaker.

One could surmise that replacing the up limit switch fixed the problem but it is hard to understand given the circuit design.  Time will tell.
 

[Fly Boomer]

1 hour ago, skykrawler said:

Update on the M20K airplane with the popping "Gear Cont" circuit breaker.  On the flights immediately preceding this activity the circuit breaker had popped two or three times after retract.

Excellent follow-up.  Thanks!

[MB65E]

What light bulb socket is under the floor? 
My right nav light won’t work with an LED lamp. Only an old Grimes bulb. Time to get out the ohm meter. 
-Matt

[Ragsf15e]

1 hour ago, MB65E said:

What light bulb socket is under the floor? 
My right nav light won’t work with an LED lamp. Only an old Grimes bulb. Time to get out the ohm meter. 
-Matt

Maybe he means the light under the manual indicator in the floor?  Mine has a very small bulb in it and the wiring is fragile, but it works fine and lights up the floor indicator.

[Yetti]

Or and this is more common than one might think.   There was a wire laying on a screw that would move a bit when the gear went up or down.   When the panel was taken off the wire was fine because that screw was out.   Of the 30 times the gear was operated, how many time was it with the panel back on?   See we will never know the true meaning.

 

[hubcap]

I had the same problem with Myrtle not long after my purchase. Replaced the circuit breaker and that solved the problem.

[skykrawler]

On 4/22/2024 at 3:29 PM, Yetti said:

Or and this is more common than one might think.   There was a wire laying on a screw that would move a bit when the gear went up or down.   When the panel was taken off the wire was fine because that screw was out.   Of the 30 times the gear was operated, how many time was it with the panel back on?   See we will never know the true meaning.

 

That was precisely the reason to inspect the wiring carefully.   In fact a trim screw that holds down the plastic strip at the bottom of the interior side panel had been replaced with a 1 inch screw and was within .25 inches of the gear control wires - but no contact.   On this airplane the gear control wiring in the belly was factory tidy. Under the instrument panel was a different story.