Altitude Encoder Problem

[GeorgePerry]

I know nothing about avionics.  With that said, my encoder is showing 300 ft low with ATC when I'm level on the assigned altitude.  Before I taxi the bird over to my avionics shop, does anyone knowledgeable have suggestions for an "easy" fix.

"I don't need to know how to build a microwave, all I need to know is how to press cook"

[piperpainter]

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[piperpainter]

From your pictures it looks like your transponder is down low while mine is up high on the right side, but I had some water get into my transponder and caused a heap of problems with it. It ended up costing me about $450 to have it fixed. But  Mine is an older Bendix/King. not sure if that helps, but maybe check for leaks!? Either way goodluck!

[piperpainter]

oops

[alun]

i had a problem with my altimeter with built in encoder was reading off by a several hundred feet.  the solution was a seperate encoder not built into the altimeter that cost me £150 (about $250). 

[Piloto]

There are four causes for altitude encoder errors:

1. Encoder connection to the static port is incomplete or leaks.

2. Encoder internal malfuction. Usually related to the internal heater.

3. Encoder wiring to the transponder. The encoder conveys the altitude data to the transponder via a 12 wire connection. If one of the wires is disconnected you will get altitude errors at some altitudes but not at others. On many occasions the disconnect happens at the transponder tray contacts. Remove the transponder from its tray and spray contact cleaner on the contacts. Reinsert transponder and give it a try. Newer transponder/encoders use 2 data wires only.

4. One of the transponder encoder inputs is defective. 

To assure that the problem is fix a biennial transponder check is the best way to go. Check the transponder altitude readout on the test set while increasing the altitude with the test pump connected to the static port. Verify there is no more than 100 feet error at all the altitudes tested. If you have a Monroy ATD-300 you can read the transponder altitude directly while climbing.

José

 

 

[GeorgePerry]

Well I learned that it wasn't an encoder problem...Turns out my airspeed indicator (which was overhauled by berkshire only 12 months ago) has a very bad leak on the static side.   With the airspeed indicator bypassed the rest of the Pitot/Static system checked +/-20 ft all the way up to 18K on the test bench.  The static system was not providing correct pressure to the blind encoder, thus the problem with altitude reporting.

Which brings me to my next question.  Has anyone ever bought a "new" airspeed indicator?  I would assume that the specific speed arcs have to be silk screened onto the replacement instrument, but a quick google search didn't really answer that question with any certainty.

I like my "old" mooney airspeed indicator, but I don't want to keep throwing good money after bad trying and keep repairing a 35 year old instrument.  So I'm considering sraping it and buying new.

If anyone has any thoughts or opinions I'd like to hear them.