Replacing a KX-170B with a MX-170C

Has anyone done this box for box replacement? Advertising says it is a slip in compatible replacement. I have a concern since the lighting of the display is different. My KX-170B has a display light dimming circuit connected to connector pin 33, as specified by the King Manual. The MX-170C interconnect diagram shows pin 33 dedicated to a VOR Test (?). This is not described in the manual anywhere and there is no definition of what the airplane side connection to pin 33 should be. Maybe it means nothing - I discussed with the mfgr and they could not answer the question.

Also pin 42 is listed as a spare by King, but the MX-170C interconnect shows it is connected to a COM Flip-Flop function - presumable from a wheel mounted push button. (but they do have a note that a resistor has to be added to the computer board). Wonder how that works if you purchase from the likes of Aircraft Spruce?

Thanks for any responses.

John

Comments

  • Scott ShererScott Sherer COO Forum Moderator
    edited June 17



    I've had five or six MX170's over the decades. I currently have a MX-170C in my plane after removing the old KX-170. They are indeed easy to install, one locking screw and then slide out and in. They work perfectly. I recommend it highly.

    Scott Sherer
    Wright Brothers Master Pilot, FAA Commercial Pilot
    Aviation Director, Cessna Owners Organization Forum Moderator and Cessna Owners Author.

    Need help? Let me know!

  • Diddo from the Avionic's Guy!

  • I recently swapped out my 170B for the MX170C in my 182. So far it's been great and having flip flop nav/com in the second radio is sweet. Easy install, I did have to remove my 430 above in order to get a grip on the old 170B to remove it but that was easy. Nothing more than old one out and new one in. ☺️
  • Scott ShererScott Sherer COO Forum Moderator
    edited June 28

    It's the greatest value in avionics, IMHO. Great job and I'm very pleased that it worked out for you! I do have a quick question for you: Do you have glideslope on that navcom?

    Scott Sherer
    Wright Brothers Master Pilot, FAA Commercial Pilot
    Aviation Director, Cessna Owners Organization Forum Moderator and Cessna Owners Author.

    Need help? Let me know!

  • If the glideslope question is for me, yes my num 2 has a glideslope and it works fine after the swap out.

  • Scott ShererScott Sherer COO Forum Moderator

    OK, the reason that I ask is that the glideslope receiver is not in the KX-170 or MX-170. It's another radio buried somewhere, probably a kn-75, if memory serves. So that radio is old, too. Keep an eye on it and test it once in a while.

    Scott Sherer
    Wright Brothers Master Pilot, FAA Commercial Pilot
    Aviation Director, Cessna Owners Organization Forum Moderator and Cessna Owners Author.

    Need help? Let me know!

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