TKM - MX 170B nav com. falied
 

I was flying a localizer approach this week when the no.1 nav com. dropped off line. There was no intermittent operation, it just stopped and no flipping of switches, breaker ect. would bring it back. I was considering switching no. 2 nav com, an identical unit,to no. 1 as a quick way of troubling shooting the supply circuit but in "googling" this radio for info and units for sale I never saw a24V unit. Are all MX170Bs 12v - Im cncerned that Cessna had some kind of voltage step down device that could have failed , if so the no.2 or a replacement radio could get "fried" . Any advice on how to proceed would be a big help.

Hello John
The original KX175 are 12v and have a KA39 converter mounted somewhere behind the panel. The MX170B use the same unit. It is quite a big unit it is black, mounted with screws either end with six wires from it, that is either end as well.
There will be 2 as the systems should be separate for safety.
Should not take much finding, must be behind the instrument panel somewhere.

Pete

If you take the cover of the KA39 off the connection are marked so that you can check the 28v in and the 12v out.

Pete - thanks, thats just what I needed.

Just as a matter of interest, I have had a complete failure of a MX385A, 3 times and this was caused by a circuit inside the radio not working correctly.
The MX170 is quite reliable, we have to fit the MX170C over as it complies with the FM immunity rules (good old British CAA).

Let me know how you get on.

Cheers
Pete

Pete:

Now I finally know what those big ugly things are in my avionics bay!!!

Thanks,

Keven
________
JCPENNEY GIFT CARD

Keven
Hey! longs they don't move its ok.

Pleased to be of help.

Cheers
Pete

John
Did you get the MX170 working again?

Pete

Pete - thanks for asking but I havent been to the hangar since my post, its cold here in Indiana. Plan on going first break in the weather - hopefully in a week and check out your suggestions as best as I can. I did get a chance to talk to my regular A&P about another issue and his remark re. finding the power supplies was -good luck- guess they can be pretty well hidden sometimes. If the power supply is Ok then plan is to move my no.2 radio up to replace the failed no.1 and look for a place to repair the failed radio. Googling around - it looks like avionics shops avoid working on TKMs so ill have to find a place to send it?

I had TKMs in my first Skymaster and the factory did a reasonable job on repairs, meaning service and price, on the one occasion when I needed repairs.

Ernie

Ernie - I have googled every combination I can think of to locate that TKM factory? could anyone help me with a phone no. or address for them - thanks

Hi John

TKM
14811 N 73rd Street
Scottsdale
AZ 85260-3107
Tel 480-991-5351

The power supplies should be easy to find as they are quite big and need some cooling.

Cheers
Pete

location
 

Hello John, This is Jerry De Santis. I love in Michigan. I get to Ind. quite an bit and my daugther lives in Bloomington. Where are you located?

Cheers!
Jerry
N34EC

Morning Jerry - the plane is based at Connersville Ind - CEV- Im about 50 mi south of there - no airports here in SE Ind where I live so I dont just run over to the hangar, its more of a day trip. You have probably noticed my post re. fuel at BMG - thats been a reqular stop when ever we are returning from west of CEV. A very good stop, especially if theres time to take the Cadillac crew car into town for a meal. Thanks to everyone for the ideas with the radio, I hope to get up to the hanger this week and look it over.

Ind
 

Hi John,

Up here in Michigan several of us do a lot of flying together. Hope you can join us one of these days. Also, SOAPA will be having our yearly flyin and meeting in Kalamazaoo (AZO) this coming May. Hope you can come. You will meet a lot of nice skymaster folks from around the country any maybe some from Canada and Mexico too.


Jerry:D

Pete - got to the hangar today, pulled both radios and put the non working no.1 in the no.2 position and it worked - so good news is radio is ok . Checked the radio power breakers and found power thru them so leads to the KA39 convertor being the suspect. I opened the exterior avionics panel and sure enough its setting there like you said. Thats probably as far as I go with trouble shooting it. We have Muncie Aviation close by and they are an avionics repair station so I will fly it up there and have them check the unit, hopefully they can even repair it. Thanks again for your help.

Hi John
Get an estimate for the repair, sometimes it is cheaper to get a used KA39.

Pete

KA-39
 

There's one for sale on ebay for a "C" note, plus shipping.

Pete - got the radio repair done today. The bi-annual static system recertification was due this month so I had Muncie Aviation look for the problem. They found a 24V feed wire to the power supply loose, reconnedted it and it works fine. Thanks for your help.

John
That was an easy repair by the sounds of it. Glad to be of help.

Cheers
Pete