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Intermittent instruments

F

FL Flier

Active Member
1. Dynon D6 - not working most of the time. I took the plane to an avionics shop, where they found the voltage at the positive pin on the connector was good (13-ish volts). It does not have a backup battery. They couldn’t figure out the issue. Sometimes the Dynon does come on all on its own; when it does it’s always on the second flight of the day, following an hour or two on the ground.

2. Tach - standard Van’s electromechanical 2” tach. The last couple flights, I get zero tach indication until the engine has been running for two minutes. Right about at 2:00 it comes to life and indicates normally for the entire flight. After breakfast at startup for the second flight it is normal from the get-go. The connections on the tach and transducer are tight and corrosion-free.

I haven’t bothered with fixing the Dynon because I only fly day VFR, and it will be well over $400 to send it to Dynon. I’m not convinced the problem is internal to the unit.

The tach, I am thinking, could have a worn end on the drive cable that expands with heat and then fits properly. Am I off the rails with that? Another possibility could be that there is insufficient voltage right after cranking, but the radios all work normally.

Suggestions for what to look at next?
 
My limited experience and knowledge would point you to wiring and connections. Every time I’ve had an intermittent electrical issue it’s been a loose, poor connection. Start with the instrument and work your way back towards the circuit breaker it’s wired to. Then do the same on the ground side. I bet you’ll find something not kosher. Use a multi meter to check for continuity and excessive resistance
 
FL Flier said:
1. Dynon D6 - not working most of the time. I took the plane to an avionics shop, where they found the voltage at the positive pin on the connector was good (13-ish volts). It does not have a backup battery. They couldn’t figure out the issue. Sometimes the Dynon does come on all on its own; when it does it’s always on the second flight of the day, following an hour or two on the ground.

2. Tach - standard Van’s electromechanical 2” tach. The last couple flights, I get zero tach indication until the engine has been running for two minutes. Right about at 2:00 it comes to life and indicates normally for the entire flight. After breakfast at startup for the second flight it is normal from the get-go. The connections on the tach and transducer are tight and corrosion-free.

I haven’t bothered with fixing the Dynon because I only fly day VFR, and it will be well over $400 to send it to Dynon. I’m not convinced the problem is internal to the unit.

The tach, I am thinking, could have a worn end on the drive cable that expands with heat and then fits properly. Am I off the rails with that? Another possibility could be that there is insufficient voltage right after cranking, but the radios all work normally.

Suggestions for what to look at next?
Click to expand...

The symptoms point to a wiring problem being much more likely than an instrument problem. Something is moving and in some portion of the movement it is happy and others it is not. I would follow the power and grd wires of those two devices backwards. Will need to measure while tugging on and wiggling wires to find it.
 
I'd remove the D6 and run it on the bench.
If you don't have a bench supply, fly over to Venice Saturday morning and we'll hook you up. Then you can grab breakfast or a great Cuban sandwich over at chef Tony's.
 
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