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D100 - D120 comms lost

rondawes

Well Known Member
I'm buying a new-to-me RV-7A with Dynon D100 and D120 units. During the demo flight, upon startup they both displayed messages that they could not communicate to each other. As we powered up for takeoff, the messages went away and the units worked normally for the rest of the flight. The current owner reports that this is "typical" for the time he's had it.

Have others seen this type of behavior? Something voltage related? Thoughts? Thanks!
 
Ron

I have the same setup. There is a pair of wires (DSAB) that connect the D100 & D120. What you're describing does not sound normal. If they are both turned on at the same time, there shouldn't be a com failure message. If they are both on and one is switched off, then there will be a "communications lost" message.
In my case, the D120 is wired into the master buss. My D100 is wired into the avionics. I start the engine & check engine guages, then switch on the avionics master. During that brief period before turning on the avionics, I do get a message. But once avionics are on and D100 activated, the message goes away.

It almost sounds like there may be a loose connection. Something doesn't seem right.
 
I'd also bet it's a loose/bad connection. I have the same arrangement and do not get this error. Well, not since I had a bad connection several years back. Just have to dive in and dig. Won't be fun.
 
Ron

I have the same setup. There is a pair of wires (DSAB) that connect the D100 & D120. What you're describing does not sound normal. If they are both turned on at the same time, there shouldn't be a com failure message. If they are both on and one is switched off, then there will be a "communications lost" message.
In my case, the D120 is wired into the master buss. My D100 is wired into the avionics. I start the engine & check engine guages, then switch on the avionics master. During that brief period before turning on the avionics, I do get a message. But once avionics are on and D100 activated, the message goes away.

It almost sounds like there may be a loose connection. Something doesn't seem right.

How long does it take for them to sync up and the message to go away? Instantly, a few seconds, a few minutes?
 
So FWIW, an update to this situation.

I flew out to pick up the plane. On the ground the D100 and D120 did not communicate. But during the demo flight, when we took off everything started working normally so I decided to fly it home to Texas. I took off and it still did not work. The D100 did it's thing fine, the D120 did it's thing fine but no communications between them. Also no HSI function on the D100 as the GPS data was not making it to the D100 either. I didn't notice if that worked or not on the demo flight but I didn't want to fly home that way. Plus, the autopilot function and the HS34 did not work either. So back to the airport I went.

We called around and one of the locals recommended an avionics tech who agreed to come look at it the next morning. We stared looking at the network status on the D100 and D120. The D100 could not see any other device on the network. The D120 could see 6 devices, i.e. itself, the HS34, AP74, the 2 servos, and the remote compass. So the D100 was the only device not talking to the others. The harness went from the D100 to the HS34. The tech had a spare HS34 setting around so he fetched it. What a simple fix this could turn out to be, just swap the HS34! Nope. No joy. His HS34 did not fix it.

So we pulled the D100, the HS34, and the D120 and started continuity checks on 2 DSAB network wires between the units. The tech thought he saw a high resistance connection between the D100 and HS34 so he fixed that. Still no joy. So he said he thought the only thing left as the culprit was the D100 itself. Sigh....

I put in a call to Dynon to talk to them. I had to leave a message for a call back. While waiting, I called Stein Air. A super nice tech listened to my story, told me he had never heard of anything similar and recommended that I really needed to talk to Dynon.

Dynon called back and again, a very helpful tech listened to the whole saga. He said that there had been a few cases where the RS485 network comm chip in the legacy units had failed and that it needed to come back to Dynon. The good news is they still repair them on a flat rate charge and warranty the repaired unit for 1 year.

So off to a pack & ship place we went and sent the D100 off to Dynon. Fingers crossed that when it comes back that all is well. We shall see.....
 
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Hey Ron

Sorry to hear the problems you’re having. But it sounds like you finally drilled down to the solution. Hopefully Dynon will get everything talking to each other.
 
And the saga continues....

The D100 came back from Dynon. I installed it and had exactly the same symptoms as originally, i.e. the D100 cannot see any other devices on the DSAB network. More talks with Dynon. They suggested sending it all in to see if they can play together on the bench. So I pulled the D100, D120, HS34, and AP74 and sent them off to Dynon. The tech emailed and send a video of them all working fine on the bench. Arghh..... So he thinks it's either (A) wiring, despite the tech in Mesa saying it was OK or (B) one of the servos.

They will send the units back and I'll install the D100 and then add the others back one at a time. I will also check the network wiring myself. I may need to disconnect the servos in the process.

I did not build the plane and the builder has not responded to my emails. So from the drawings, I think I see the location of the roll servo access panel under the wing but don't know if it's on the right or left side. Is there a standard for which side to place the roll servo? Or is it builder choice?

I'm less sure about how to access the pitch servo. Pull the baggage bulkhead?

Advice on servo locations would be greatly appreciated. BTW, this is an RV-7A.

Thanks, Ron
 
Servo locations

Ron

Odds are the pitch servo is just behind the elevator bell crank which is behind the baggage bulkhead. You'll have to take both parts off.

The common position for the roll servo is behind the right aileron bell crank access panel.

Carr
 
Ron

Odds are the pitch servo is just behind the elevator bell crank which is behind the baggage bulkhead. You'll have to take both parts off.

The common position for the roll servo is behind the right aileron bell crank access panel.

Carr

Thanks! Will check the right side first.
 
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