On my last flight I turned on the pitot heat but the indication showed a failure to come on and there was no amperage increase like I normally see. Once back on deck I checked to see if the pitot heat 10 amp fuse had blown but it was still intact. Next step was to remove the left outboard wing inspection plate and check for voltage at the heat controller connector. Voltage was good so it had to be either a bad pitot tube (low probability) or a bad controller box. Both of those units have been in the aircraft for the last 9+ years and have worked flawlessly until now. Clearly out of warranty but I still reached out to Dynon for some troubleshooting tips.
To troubleshoot the Dynon pitot tube I disconnected all the leads and checked for resistance based on the input that Dynon provided. Resistance between the black and orange wires and the black and blue wires should be 2.5 ohms. Resistance between the two thermistor wires (small connector) should be 10 kilo-ohms. All of those readings were close and Dynon said they vary slightly from tube to tube. So that left the pitot heat controller box (PN 100640-000) and Dynon said there was no fixing that, a new replacement would be $278 plus shipping.
Since I had to remove the controller box anyway I figured I'd take a look inside before spending $300 and pitching the old box. When I removed the controller box something was rattling inside like a maraca. Opened up the box and found a diode that had broken lose from the circuit board.
There's four nuts that hold the board in place and a wire stay on each side that has to be removed before you can access the back side of the circuit board. Since Dynon would not repair the unit I figured I'd dust off my best EE skills and try to solder the diode back in place. I carefully drilled out the old solder, held the diode in place (banded side goes at the top of the diode arrow diagram on the board) and soldered it back onto the board. Added some solder on the top side too for good measure to sandwich the connection in place. Put it all back together, connected it up and it's back to working. If you find that the diode leads are broken off, Dynon provided the specs for a new diode: DIODE SCHOTTKY THD DO-201AD 45V 12.0A
So hopefully this might help someone with the same or similar issue before you go spending big $$$ for a replacement. Worst case, if I goobered up the circuit board, I'd order the new controller.
To troubleshoot the Dynon pitot tube I disconnected all the leads and checked for resistance based on the input that Dynon provided. Resistance between the black and orange wires and the black and blue wires should be 2.5 ohms. Resistance between the two thermistor wires (small connector) should be 10 kilo-ohms. All of those readings were close and Dynon said they vary slightly from tube to tube. So that left the pitot heat controller box (PN 100640-000) and Dynon said there was no fixing that, a new replacement would be $278 plus shipping.
Since I had to remove the controller box anyway I figured I'd take a look inside before spending $300 and pitching the old box. When I removed the controller box something was rattling inside like a maraca. Opened up the box and found a diode that had broken lose from the circuit board.
There's four nuts that hold the board in place and a wire stay on each side that has to be removed before you can access the back side of the circuit board. Since Dynon would not repair the unit I figured I'd dust off my best EE skills and try to solder the diode back in place. I carefully drilled out the old solder, held the diode in place (banded side goes at the top of the diode arrow diagram on the board) and soldered it back onto the board. Added some solder on the top side too for good measure to sandwich the connection in place. Put it all back together, connected it up and it's back to working. If you find that the diode leads are broken off, Dynon provided the specs for a new diode: DIODE SCHOTTKY THD DO-201AD 45V 12.0A
So hopefully this might help someone with the same or similar issue before you go spending big $$$ for a replacement. Worst case, if I goobered up the circuit board, I'd order the new controller.
