Alt Encoder - Which one?

[GeorgePerry]

I've got an old Narco AR-500 (25 pin) encoder paired to a KT-76C.  Over the past few months the encoder output accuracy has been getting worse.  Today I was flying VFR at 5500 and the encoder displayed 5200 to ATC.  I just had my pitot static / Xponder cert done last May and it passed with no issues.  As with most avionics problems it seems to be intermittent, but 300 feet off is not IFR legal, nor is it smart to fly VFR like this with ATC fussing about the miscompare.

I've decided to replace the encoder and I'm contemplating my choices.  Right now I'm leaning towards a Narco AR-850 (25 pin) as a replacement.  Primarily because it's plug and play with no additional wiring required.

My question to the group is:  Does anyone rec. a different type of encoder (25 or 15 pin) and why?

[Piloto]

Before replacing the encoder clean the contacts at the encoder and transponder tray with contact cleaner. Your problem may be caused by contact oxidation. Also verify your altimeter setting does match the airport baro-pressure when set to the airport elevation. Check the static line to the encoder for kinks and cracks. The location of the encoder should be in a ventilated area to avoid overheating that may induce errors.

José   

[GeorgePerry]

thanks José.  I wish it were a simple fix but the bench check showed the AR-500 is on it's last breath.  I've ordered an AR-850 as a replacement.  I got a reconditioned unit from wentworth aircraft for 1/4 the cost of a new unit.  it's going in tomorrow.  Hopfully that'll do the trick

[OR75]

direct replacement is the way to go !!!!!  whenever you can

whenever there is rewiring needed, it always cost more than it should, not counting the downtime, logistics to get to the shop and the collateral damage !!!

 

[RJBrown]

http://www.aircraftspruce.com/catalog/avpages/at150_ar850.php

Aircraft Spruce has it new for $384. Ad says it is plug n play for your 500.

[GeorgePerry]

Wentworth aircraft had a refurb unit for $90 with a bench check prior to shipping.  It's solid state, so I'm betting it'll work just fine.

http://www.wentworthaircraft.com/