AXP340 long delay for Press Alt at startup

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   Recent problem with my AXP340.   Was fine for past year or so....
Most days, on first flight of the day, I don't get Pressure altitude output for 10 minutes or so.  It starts in ALT mode and transponder squawk works fine, but The AXP screen shows Pressure Altitude shows FL---.  After 10 minutes or so, the AXP340 starts reporting the correct Press Alt.

This started a few weeks ago.  No recent panel work done.

Any troubleshooting suggestions?

Joe Brunski
1977 C-177RG with two IFD540s + AXP340 + MLB100

Edited by CardinalRG - 12 Nov 2016 at 5:01pm

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CardinalRG Members Profile Send Private Message Find Members Posts Add to Buddy List Newbie Joined: 02 Aug 2015 Location: Canada Status: Offline Points: 12	Post Options Post Reply Quote CardinalRG Report Post Thanks(0) Quote Reply Topic: AXP340 long delay for Press Alt at startup Posted: 12 Nov 2016 at 4:44pm
	Recent problem with my AXP340. Was fine for past year or so.... Most days, on first flight of the day, I don't get Pressure altitude output for 10 minutes or so. It starts in ALT mode and transponder squawk works fine, but The AXP screen shows Pressure Altitude shows FL---. After 10 minutes or so, the AXP340 starts reporting the correct Press Alt. This started a few weeks ago. No recent panel work done. Any troubleshooting suggestions? Joe Brunski 1977 C-177RG with two IFD540s + AXP340 + MLB100 Edited by CardinalRG - 12 Nov 2016 at 5:01pm

DavidBunin Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 20 May 2015 Location: Rockwall, TX Status: Offline Points: 742	Post Options Post Reply Quote DavidBunin Report Post Thanks(0) Quote Reply Posted: 18 Nov 2016 at 8:08am
	Sounds like the heater is going out in your altitude encoder. Altitude encoders normally contain a heater to bring the pressure sensor to an above-ambient operating temperature (usually around 140°F) which means they can eliminate temperature as a variable in the pressure sensor logic. Most encoders have a warm-up time of no more than 30 seconds before they go valid. Have your altitude encoder removed and bench tested at an avionics shop. My guess is you'll be buying a new one. They are not terribly expensive. David Bunin