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Help! TruTrak Digitrak won't work

Snap

Well Known Member
Hey guys, we just installed a used Trutrak Digitrak that (as per the seller) has been working since beeing pulled out. I soldered the harness myself and we installes everything in out RV-3, the servo in the left wing tip.

When we power the unit up, it'll apply a moment on the servo, but the servo won't move in any way. We're not able to get a GPS fix, too but the manual states, that the unit will work in track hold mode without GPS an in heaging hold mode with GPS.

Has anybody ever had that? Thanks ahead
 
Check the wiring, particularly the autopilot disconnect/CWS mode.

The GPS fix has to come from an external source via a serial input.

When you get it sorted - always make sure you switch the unit on when stationary, otherwise it can confuse it.

Have you got the complete installation guide ? If not, send me a PM or email and I can forward.
 
Double check pins 1,2,3,4, and 5 at the servo. If the servo arm bounces back and fourth but doesn’t move, it is likely short on one of those.

As to the GPS input, if it’s from a handheld, also make sure the handheld shares a common ground with the autopilot.
 
Thanks Mark and Andrew for the input!

We haven't installed the disconnect switch yet, therefore I don't think it could have to do with it.

GPS signal comes from a Holux GPS reciever that is used to get a ADSB-Signal out of the TQ Transponder, see link below:

https://www.tq-group.com/en/products/tq-aviation/aviation-accessories/ads-b/

@Andrew: The Servo Arm doesn't bounce, it jams slightly when powered up and can be moved to any position and will stay there. No intention from the servo to move by itseld in any way.

Will the autopilot work without a GPS signal? The manual states it would, but right now it won't do anything.

Thanks again guys!
 
A big thanks to you Andrew.....

You helped us with our Digitrak, we found a new head and all is well.

Simon - Listen to the man :D:D:D:D:D
 
Will do all that, Andrew. Thanks! Will come back to this thread as soon as we were able to check on the airplane again.
 
Hi Andrew,

yesterday we found sufficient time to look into the matter piece by piece. Wiring from Head to Servo is 100% correct - we double checked it plus checked for false connections - all is fine.

We checked the servo motor itself, it is fine. We installed another servo motor at the controller, it showed the same symptoms as our stepper motor, therefore it must be something in the controll unit, either the head or the control unit at the servo. We found, that the JM17AG LM2576HVT -ADJ P+ voltage regulator only puts out 0,65 volts on pin 2, even when torque level is set to high (12 on the head unit). Feedback voltage on pin 4 is 1.3 volts.

We put 2.5 volts on the pin 2 with an adjustable DC supply and the servo worked as it should - we tested it as per the manual with the left and right turns etc.

We'd like to know whether it's the voltage regulator on the servo that has failed or the head that isn't putting out the correct signal for the voltage regulator to work properly.

Can you tell us what signal is send on pin 7 on the head to the servo? We'd like to check on this first prior to soldering out the voltage regulator. We have an oscilloscope handy if we'd need it.

Thanks for your support!
 
Pin 2 output from the control head is 0-5 volts to control the torque of the servo. You should see 5 volts (or very close to it) when the torque is set to 12.
 
Thanks Andrew for your reply! We'll check that to know whether the head is putting out too low of a voltage or the voltage regulator is faulty.

Just to be sure: It must be Pin 7 at head and Pin 6 at the servo as per manual, right?
 
Okay, we measured PIN 7 at the Head, respectively PIN 6 at the servo for the roll control voltage. The Torque level was set to 12 on the head. First we measured 4.9 volts. Then we set the torque level to 6 and measured 0 volts. Then we set it back to 12 and measured 0 volts.

Seems as if the head is putting out wrong voltages for the torque control. We'll double check with an adjustable voltage regulator on the PIN 6 at the servo and look whether it works then.

Any comment on that, Andrew? Thanks again for checking in!
 
Was the measurement done at the control head or at the servo? With the servo connected?

Double check that there isn't an intermittent short to ground/another pin. The voltage being correct one moment then not correct the next sounds very strange.
 
Sorry to jump in here with a smart a** question, but in your first post you mentioned “solder”. Not doubting your skills but soldering these small d sub pins is a tough and tricky job.

Combine that with some of the symptoms described and it makes me wonder

I tried soldering some d subs early on and found crimping to be superior in many ways.

In any case, good luck and hope you track down the problem.
 
Hi Andrew, the measurement was done at the end of the harness at the 9 pin plug for the servo, with the servo disconnected.

We will triple check the wiring, thank also to @Gary for that input.

I'm pretty sure I did a good job with the soldering iron, I've done such jobs like solderings ICs on control units several times. When checking the correct wiring we also checked every single pin to all the others for short circuits and didn't find anything suspicious.

Will keep you posted!
 
We got it working! Finally. :)

Unfortunately it sometimes deviates from the track by 3-10°, holds that new track and then slowly moves back after 30-90 seconds. This will set you off course. Happens about 3-4 times per hour flight time. The numbern on the head won't change, but the track.

Anyone else with this problem? Thanks ahead.
 
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