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Garmin GSA 28 blows fuse for Ray Allen Trim Servos

With the G3X auto pilot off my Ray Allen trim servos operate normally with the 4 way hat on the pilot stick. I have a single toggle switch to power the Garmin GSA 28 servos and as soon as power comes on for the servos it pops the fuse for the trim servos. My system calls for a 1 amp fuse for both pitch and roll trim servos (same circuit). I have put a 4 amp fuse in place and it still immediately trips the fuse when the servos are powered up. I have a G3X with GFC 507 controller, new system not yet flown.

I have pinned out all connections and the wiring is good. With the GSA 28’s off (no power) the Ray Allen trim systems operates normally. This confirms the wiring, in my mind. Is there a spike when the GSA 28’s see power that trios the fuse? Autopilot also works and checks fine but won’t auto trim because the trim motors are disabled with the blown fuse.

The relays are not required because I do not have the trims wired to the co-pilot stick. Just one stick is in control. RA stick grip is the G307, wiring attached below

RV-8A
 

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The Ray Allen Trim servo's have an average amperage pull of 0.2 with a max amperage pull of 0.2.
The GMC 507 has an average amp pull of 0.1 with a max of 0.1.
The GSA 28's each have an average amp pull of 0.4 with a max of 2.8 each.

I had 3 GSA 28 autopilot servo's feeding off the same 7.5 Amp breaker with 20 AWG wire running to each of them (and back to ground).

Remember, the breaker is to protect the wire not the component. It sounds like you may have a short somewhere and the breaker is protecting your wiring. But difficult to diagnose without a multimeter and your electrical drawing diagrams.
 
Is this a new power up panel or one thats been in service for a while operational? May help in troubleshooting. Sounds like gound and power between the two devises may have got rolled somehow. Maybe confirm with VOM that 12 vdc is on correct terminals and polarity correct. Without diagram, hard to diganose, but best of luck in the process.
 
+1. Need wiring diagram. You cannot simply parallel existing trim wiring (including hat switch) and autopilot trim commands, without asking for trouble.
 
Keep in mind the RayAllen servo system by design swaps ground and power to reverse the direction of the DC servo motor. To tie that AP system in to that may require some isolation relays to keep the systems electrically separated.
 
Is this a new power up panel or one thats been in service for a while operational? May help in troubleshooting. Sounds like gound and power between the two devises may have got rolled somehow. Maybe confirm with VOM that 12 vdc is on correct terminals and polarity correct. Without diagram, hard to diganose, but best of luck in the process.

It is new system, has not been flown yet, just finishing the build
 
Rough surface,

You will want to review page 27-12 of the Rev. AP G3X Touch Installation Manual.

TrimSwitch.png

The trim logic of the G3X Touch system requires that the input pins (11,12) on the GSA 28 servos see +12V on one pin and GND on the other pin for one trim direction, and the reverse of this logic for trim in the other direction. This is done for safety reasons to prevent a simple failure of the trim switching from causing a trim run-away.

According to your wiring diagrams, your installation is simply applying +12V to pin 11 in one direction and applying +12V to pin 12 in the other direction.

If you don't have a GAD 27, you will need to add a simple relay deck (which provides separate pitch/roll control) that is actuated by your stick grip switches to create the required drive logic with your existing stick grip.

Update: Looking at the Ray Allen wiring diagram for the G207 stick grip, it seems possible to use that stick grip without a relay deck. You should probably re-check your wiring against the RA diagram.

If properly wired, there is no reason that applying servo power would cause the fuse providing power to the stick grip to blow. The stick grip shouldn't even be outputting a power signal until one of the trim switches is pressed. When servo power is applied, the bypass relay inside the servo opens, and the trim inputs on pins 11,12 are no longer directly connected to the trim motor outputs on pins 13,14.

I wouldn't increase the size of the stick grip fuse above what the manufacturer recommends. This could damage the stick grip and perhaps other system components.

I would do some basic trouble shooting with a meter and the power off to find the wiring path that is shorted to ground. You can also unplug both servos, and plug them back in one at a time to further isolate the wiring problem. According to your wiring diagrams, you have an unusually large number of connectors in your system, which adds to the complexity.

Steve
 
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Rough surface,

You will want to review page 27-12 of the Rev. AP G3X Touch Installation Manual.

View attachment 19891

The trim logic of the G3X Touch system requires that the input pins (11,12) on the GSA 28 servos see +12V on one pin and GND on the other pin for one trim direction, and the reverse of this logic for trim in the other direction. This is done for safety reasons to prevent a simple failure of the trim switching from causing a trim run-away.

According to your wiring diagrams, your installation is simply applying +12V to pin 11 in one direction and applying +12V to pin 12 in the other direction.

If you don't have a GAD 27, you will need to add a simple relay deck (which provides separate pitch/roll control) that is actuated by your stick grip switches to create the required drive logic with your existing stick grip.

Update: Looking at the Ray Allen wiring diagram for the G207 stick grip, it seems possible to use that stick grip without a relay deck. You should probably re-check your wiring against the RA diagram.

If properly wired, there is no reason that applying servo power would cause the fuse providing power to the stick grip to blow. The stick grip shouldn't even be outputting a power signal until one of the trim switches is pressed. When servo power is applied, the bypass relay inside the servo opens, and the trim inputs on pins 11,12 are no longer directly connected to the trim motor outputs on pins 13,14.

I wouldn't increase the size of the stick grip fuse above what the manufacturer recommends. This could damage the stick grip and perhaps other system components.

I would do some basic trouble shooting with a meter and the power off to find the wiring path that is shorted to ground. You can also unplug both servos, and plug them back in one at a time to further isolate the wiring problem. According to your wiring diagrams, you have an unusually large number of connectors in your system, which adds to the complexity.

Steve
Thanks Steve, I have NOT checked the stick yet but that's because the trim works with no problems without the A/P powered. I am going to the hangar right now to check the stick just to be sure. I have a CPC connector at the base of the stick and if that is disconnected the fuse does not blow but I have no trim power either. I have already isolated each trim motor from the system in separate tests and that did NOT solve the issue. Even when both trims are out of the system the fuse blows so the stick needs to be check for sure.
 
Thanks Steve, I have NOT checked the stick yet but that's because the trim works with no problems without the A/P powered. I am going to the hangar right now to check the stick just to be sure. I have a CPC connector at the base of the stick and if that is disconnected the fuse does not blow but I have no trim power either. I have already isolated each trim motor from the system in separate tests and that did NOT solve the issue. Even when both trims are out of the system the fuse blows so the stick needs to be check for sure.
Yes, nothing is making sense here, so it is probably a wiring error.

If the stick grip looks ok, I would plug in one GSA 28 servo at a time, then apply power to see if you can further isolate the problem to one servo connection or the other.

Steve
 
Youre saying that the trim doesn't work if the AP isn't engaged? That doesn't seem right. I still must be missing something.

The trim works normal but once the A/P servos are powered up the trim motors fuse blows. This is a Garmin system with auto trim built into the A/P
 
Youre saying that the trim doesn't work if the AP isn't engaged? That doesn't seem right. I still must be missing something.

No. I'm saying if the A/P goes wonky, a kill switch can be an easy way to shut off power to the servos without impacting the trim system.
 
Yes, nothing is making sense here, so it is probably a wiring error.

If the stick grip looks ok, I would plug in one GSA 28 servo at a time, then apply power to see if you can further isolate the problem to one servo connection or the other.

Steve

Just checked the stick grip and everything checks correct based on Ray Allen wiring diagram

I have attached the RA wiring diagram on the first post in this thread
 
Just checked the stick grip and everything checks correct based on Ray Allen wiring diagram

I have attached the RA wiring diagram on the first post in this thread

I looked over your diagrams in depth and it shows the power from the main buss running to the servo properly, but because you aren’t using a GAD27 or DPDT switch I don’t see any path for the power to return to ground.

Not sure how the trim is even running unless you have a short in the system somewhere that is returning the power to ground. It may also be going to ground via the GSA 28 while it is turned off.

This is a guess, but because the ray Allen only pulls around 0.2 amps, you are likely not reaching your amperage limit on the fuse even with a short running through the Servo. When you power on the GSA28 you are adding the 2.8 amps that the GSA28 can provide to a likely short and blowing your fuse.

The root of the problem seems that you have no ground for the power to return from the servo. Not enough information on the switch in your stock grip, but that should be a 3 position DPDT switch that allows the power to return to ground. That is not shown in your drawing diagram and likely your culprit.

But that is just my guess based on the information available.

I’ll send you a note with my number, but if they are wired like this then it shouldn’t even be working
 
No. I'm saying if the A/P goes wonky, a kill switch can be an easy way to shut off power to the servos without impacting the trim system.

Hi Kyle

Isn't that what the AP disconnect is for? Or is this some additional safety feature that beyond the scope of the G3X architecture as designed? Is it recommended in the manual? How real is this failure mode?

I'm not trying to be argumentative, just trying to understand the logic since I'm planning a G3X with auto trim install in the near future.

Thanks

Laird
 
Two on off switches

Hi Kyle

Isn't that what the AP disconnect is for? Or is this some additional safety feature that beyond the scope of the G3X architecture as designed? Is it recommended in the manual? How real is this failure mode?

I'm not trying to be argumentative, just trying to understand the logic since I'm planning a G3X with auto trim install in the near future.

Thanks

Laird

So in my G3x i have an on off switch for the ap power that goes to the ap servos and gmc507 and another pullable circuit breaker for the trim power that is reachable by the pilot for the runaway trim situation. I think the trim power needs to be reachable by the pilot in case of runaway trim.
 
Hi Kyle

I'm not trying to be argumentative, just trying to understand the logic since I'm planning a G3X with auto trim install in the near future.

Thanks

Laird

It is probably overkill. I've got that switch stashed at the top of the panel in an "always on" configuration. I figure if something goes wonky in the trim/AP system, I can take that (the AP) out of the equation very quickly. I have a similar switch for the trim system. One thing with the -10 is the control forces get really high (compared to the -6) if it is out of trim. A way out of trim situation on the -10 would be a lot harder to handle than in the -6 and I want the ability to stop a runaway trim situation very quickly.
 
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Just checked the stick grip and everything checks correct based on Ray Allen wiring diagram

I have attached the RA wiring diagram on the first post in this thread

Thanks. Nothing making sense here. Some facts to consider.

1. When the GSA 28 servo is powered up, ALL of the power to drive the connected trim motor (using speed scheduled pulse width modulation (PWM)) is provided by the GSA 28 servo - not the signals coming into the servo trim input pins 11,12. There is zero reason why the fuse connected to the stick grip trim switches should see any significant power since these switches are no longer powering the trim motors - just providing low current trim hi/lo signals to the GSA 28.

2. The GSA 28 servo trim signal input pins (11,12) should read about 2.4 Vdc each when the servo is powered up and nothing is connected.

3. I applied 12 Vdc to each of the GSA 28 servo trim input pins (11,12) for a powered servo to emulate the signal provided by your stick grip and the measured current flow into the servo trim input pin was only 0.1 mA. Again, absolutely no reason why the trim switches on the stick grip should be providing any noticeable current to the powered up GSA 28 servo or blowing a fuse.

Steve
 
Jon,
The Ray Allen wiring diagram shows power and ground to each switch controlling the servos. Is that incorrect.

Gary
 
Jon,
The Ray Allen wiring diagram shows power and ground to each switch controlling the servos. Is that incorrect.

Gary

The stick grip wiring diagram is good and would provide the necessary power, but the stick grip diagram also doesn’t match the power diagram showing how the fuse connects through the stick and other connectors. The diagrams aren’t matching up in this case.

Very difficult to diagnose a problem when the diagrams don’t line up and that is all that is available. Also, only one person knows if the diagrams match the aircraft.
 
Thanks. Nothing making sense here. Some facts to consider.

Steve

I have found that in general, troubleshooting defies most logic, it's the illogical things that cause the problems, so using the standard "it should work" logic usually doesn't work. Just start ringing things out and verifying connections and you will likely stumble onto the problem :D
 
Resolved

I had the "Garmin Reversing Adapters" plugged into the servos. These Garmin blocks are only when you want to unhook the servos and you use the adapter block to allow the manual trim to continue to work without being plugged into the servo. Crazy but thought these "reversing adapters" were Terminators for the Can Bus. When the servos are at each end of the Can Bus the terminators are not required. Unfortunately I spent a lot of time to learn this so I hope this helps someone else with the silly thing I did
 
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