Encoder errors with D10A with Encoder Converter

[Searey_Lee]

Encoder output is OK between 1000 and 2800 but PA output decreases with altitude. This is unacceptable in Class C airspace and I was lucky not to get thrown out.
The indicated altitude on the D10A display agreed with my other altimeter. But, the encoder output indicated on my Microair T2000 transponder decreased with altitudes above 2800.
For example:
1000 to 2800 on D10A : 1000 to 2800 on T2000
3500 on D10A: 2000 on T2000
4000 : 1400 on T2000
Altimeter setting was 29.95

This problem has become apparent in the last 2 weeks.
Is this wiring or a faulty encoder converter, or EFIS?

 

[jakej]

If the system was recently wired or used for the first time in Class C then maybe it's a wiring issue. If that's the case then the first & least costly thing to do is check the wiring - I've not had a problem with the converters

Jake J

 

[Dynon]

So the encoder converter's gillham/gray code output is a bit like binary, but it has some unique properties, such that only one bit changes for any given altitude change. In your case, it sounds like things change at 2800 feet. If you look at this chart, you'll notice that the A4 wire (white w/ blue on our converter wiring) is 0 until 2800, at which point it flips to 1. So if that wire weren't connected (or the encoder were broken and not transmitting a signal on that wire), something being up with that wire would cause normal altitudes to be transmitted below 2800, and incorrect ones above it.