760 Transceiver fail

[GreggCuoco]

Hey guys,
I have a new Zenith Super Duty with the Dynon SkyView.
I have the 760 transceiver,
10 total hours on the plane and SkyView system.
The original 760 transceiver failed at 6 hours,
Dynon sent a replacement,
That replacement failed after 3 hours.
New plane, new Rami antenna, new coax built by Aircraft spruce.
SWR check is perfect.
Installing the first (original) and second transceiver they both worked perfect until they didn't,
The most recent transceiver ground checks normal, we're flying it tomorrow for the first time with this third transceiver.
Have any of you had a 760 failure ??
Is there a 760 issue out there ??
How can I have two failures in 10 hours ??
Thx
Gregg

 

[Rhino]

Definitely sounds weird, but I don't recall this ever being reported here before. Then again, I'm getting old and senile, so....

 

[jnmeade]

No experience with this radio here.
Can you describe the failure?
What does Dynon say about it?
My initial reaction to your post is that it is not likely the radio, but rather some other electrical issue. (I question that you got two bad radios.)
Does the 760 have a function that can handle high VSWR? In other words, does it reduce power or shut down if the VSWR is out of range? If not, an intermittent in the antenna system is a possible culprit to blow the finals. Has Dynon given you a post-mortem on either of the ones you sent back?
How about overheating? Is it possible the radio gets too hot?
When the radio goes bad, does it ever come back on again, in the air or on the ground, engine running or not running?
Good luck.

 

[GreggCuoco]

No experience with this radio here.
Can you describe the failure?
What does Dynon say about it?
My initial reaction to your post is that it is not likely the radio, but rather some other electrical issue. (I question that you got two bad radios.)
Does the 760 have a function that can handle high VSWR? In other words, does it reduce power or shut down if the VSWR is out of range? If not, an intermittent in the antenna system is a possible culprit to blow the finals. Has Dynon given you a post-mortem on either of the ones you sent back?
How about overheating? Is it possible the radio gets too hot?
When the radio goes bad, does it ever come back on again, in the air or on the ground, engine running or not running?
Good luck.

"My initial reaction to your post is that it is not likely the radio, but rather some other electrical issue"
I have been racking my brain thinking the same however the radio works perfect until it fails.
I would think a wiring issue would show itself all the time.
"Has Dynon given you a post-mortem on either of the ones you sent back"
Post-mortem on the first radio I was told the transceiver failed bench test, they sent out another one.
The second failed transceiver I was told "Technicians did find a noisy power supply and the unit failed initial testing. There was definitely an issue with it. It doesn't appear to be an overheating issue. Thermal analysis doesn't indicate anything abnormal"
SO IM ASSUMING I HAD TWO TRANSCEIVERS FAIL ??
"When the radio goes bad, does it ever come back on again, in the air or on the ground"
The first failure the radio was dead, the second failure the tower could be heard faintly once we got within a 1/4 mile.

 

[jakej]

Definitely sounds weird, but I don't recall this ever being reported here before. Then again, I'm getting old and senile, so....

Weird to me as well & I have done a LOT of installs .

 

[Rhino]

I would think a wiring issue would show itself all the time.

In 48 years working avionics, I'd say at least a third of the wiring issues I've encountered after initial installation have been intermittent. I'm in no way saying that's the case for you here. I just advise against making an assumption like that.

 

[GreggCuoco]

In 48 years working avionics, I'd say at least a third of the wiring issues I've encountered after initial installation have been intermittent. I'm in no way saying that's the case for you here. I just advise against making an assumption like that.

Good advise, thank you.
If this third transceiver goes south I'll get into print with DYNON tech support (they are great) and see what I can find.

 

[jakej]

Gregg - my money is that the issue is not with the radio itself but more likely a wiring/antenna/coax cabling issue if your 3rd one fails then you’d have to agree IMO. I have never heard of a similar issue with the Dynon radio like Rhino & we’ve been here a long time.
This is an example of what can happen -
A friend had his plane (composite) into a shop for reported reduced range of his transponder. Bench test was done = all ok. Next time they replaced coax with RG 400 = still the same issue.
I had an idea (based on another experience) & suggested we have a visual check of the systems. A visual check was started at the antenna & within 30 seconds the ‘culprit‘ was discovered - there are 4 segments (@ the antenna BNC ) where the pin, from the cable BNC fitting, pushes into that socket. Two of them were broken off - that was the source of the problem. Just goes to show & my take away is don’t discount anything . Jake
Ps - do you have the RG400 cables fitted to the Zenith ?

 

[GreggCuoco]

Third transceiver failed within 15 minutes.
It's time to look at my plane.
I'll keep you posted.

 

[GKC Aviation]

Get someone to SWR check your antenna from the transceiver end (so coax and antenna together)
If your SWR is way out, it will damage the radio.
Most modern radios have protection built in, I don't know if the 760 does or not.
I know with the older radios, if you transmitted into very high SWR (such as if your coax fell off the antenna or open circuited, it would blow the radio. The signal reflected back down the coax does the damage.
Usually with a SWR/power check, we look for forward and reflected power. Forward power is somewhere up near the output power of the transceiver (6 watts for the 760), and reflected power to be less than 10% of that. Higher the SWR, the more reflected power.
Just a thought, as I couldn't imagine anything else airframe related that would kill the radio. (other than kill it straight away like having power and ground around the wrong way)

 

[GreggCuoco]

Already preformed an SWR at the transceiver,
Coax and antenna were under 2
I’m at the hanger right now shooting wires.
So far all checks out.

 

[jakej]

So now we know the ‘fault’ is not a radio failure but a wiring/airframe issue - very sorry to be so blunt however you really need to double check the wiring & start at the wiring connector with it disconnected from the radio -
1. Turn the radio power on
2. Using a multimeter (ground the negative lead) &, with the positive lead, check every pin to determine if you’ve accidentally ( things happen) connected power to a pin that should not have power to it. Good luck.

 

[GreggCuoco]

Hey Jake,
Thank you for the reply.
Yesterday I disconnected the radio, the comm head and the intercom.
I pulled out the prints and confirmed every single wire, pin, power and ground.
Per print every pin to pin showed normal wire continuity which tells me it’s wired correctly.
Then I checked every wire for short to ground.
I found nothing.
With comm head and intercom connected and and radio disconnected with power on I did not chk random power to other pins on the radio connector.
I’ll do that today.
Interesting how the first radio lasted 10 hours, the second 3 hours and the third 15 min.
I’m going to ask DYNON if all three had the same failure,
If it’s my plane then all three should fail the same.
Thx for the suggestion.

 

[jakej]

Hi Gregg - you can DM me if you like.
Given the number of 760 units ‘out there’, & possibly no similar reports, I figure 3 in a row for 1 user indicates to me there most likely is an airframe issue. Although you confirmed no ‘shorts to ground’ what I suggested was finding out if there was power being delivered to a pin different to the normal 12v input.