"Colin Kingsbury" wrote in message link.net...

1979 172 with original Cessna (RT-385 IIRC?) radios, the NAV frq display on
the #1 box failed and the partners now finally agree it's not worth
repairing.

1. Replace with a slide-in replacement like the TKM series, which will get
me a new box and standby freqs (woo-hoo!)

No question this would be the cheapest alternative.

I have a TKM 170B (slide-in replacement). I know others who have
slide-in replacements for the Cessna TKM radios.

Generally we're happy with it. It is lower-power than our KX170B;
ATC will lose our tranmissions on the MX at distances where we're
fine on the KX. The nav radio is fine.

Caveat: our other nav/com is the same wiring harness. Thus we were
able to swap slots and determine that the antenna and wiring harness
were not problematic. If you can do this, fine. If you can't, I
would try to get your avionics guy or a fellow Cessna owner to loan
you a radio and test the wiring/antenna splitter etc.

I know people who say the TKM radios are junk, and I think actually
their problem is elsewhere in the system. Don't overlook the issue
that you ARE reusing the wiring/antenna etc.

2. Replace with an IFR GPS/Com. This addresses ADF/DME, but costs us one
VOR. I don't think people will go for buying a second nav/com as well so it
needs to be a one-box upgrade.

There's no question that this would get you the most increase in
capability. Depending upon where you fly, an approach certified
IFR GPS is a real boon. And, if your ADF is flaky, this might even
be the most cost-effective alternative, better than repairing/replacing
the ADF AND the nav.

The GPS can serve as a 2nd VOR just fine -- it will give you more
precise identification of intersections as well as a legal substitute
for DME and NDB.

The flaky audio panel might be a wiring issue. Again, if you can
find someone w/ the same make and model, simplest thing to do is
to swap it. While yours is out, just look it over with a multitester
for signs of bad connections etc. Hit the pins with tuner cleaner
and reseat a few times.

A little TLC definately improves the performance of old avionics.

Cheers,
Sydney