Once upon a time, TKM designed and built it's own CDI (VOR/ILS/GS) that was completely solid state. LED indicators, not swinging needles. With the new ownership at TKM, they no longer make nor support the unit (but did give me the name and number of an individual that does). I have two - one is connected to the SL30, works perfectly. I was hoping to use it with the 355 going in next spring but after discussions with the Garmin engineers, it doesn't talk to the MC60. If you've got an SL30, or a TKM unit with a resolver, this is a great unit. $250 plus a bit for shipping (I still have the original packing). I'm keeping the SL30/MC60 by the way. I like redundancy.