Because a topic like this never gets too old

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.

I'm contemplating two options:

1. Replace with a slide-in replacement like the TKM series, which will get
me a new box and standby freqs (woo-hoo!) Anybody here have those, or
suggest others? Advantage here is v. low cost to install versus something
like a KX-155 upgrade which would require rewiring, 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.

Current stack has 2x Nav/Com, 1x ADF, 1x Mode C, Audio panel w/ marker
beacon, and an M1 Loran, all original equipment. The audio panel's getting
fussy and the ADF won't lock on to the lower-powered beacons until you're on
top of them. If it was up to me I'd yank it all but I've got 4 other guys
who fly less and almost never fly IFR so they're less picky.

Best,

Hi,

I had a similar dilemma with an upgrade to factory original '76
Cardinal (with a "NavPack II", no less!) I think this comes down to
what you are trying to accomplish: if you simply want to rectify a
current problem, you have two choices: get another RT-385 ($500-700,
may not be the end of it, though) or an MX-385 ($1500 but will likely
last a while). If you are using the current situation as an excuse to
gain more capability (nothing wrong with that !), then you have to go
to an IFR GPS, KX-155's won't let you do an approach or go direct any
more than the old ARC radio. Now you are talking some serious dough,
however: your -385 may channel a remote glideslope, so that will have
to be re-done or moved around to the #2 spot. Otherwise, your "one
box" is basically starting to look like a Garmin 430, a $10K+ venture.
Legal hair splitting aside, in practical terms, the GPS does fully
replace ADF/DME, but you definitely want to keep a VHF glideslope for
now, the GPS won't get you as low when it counts.

I ended up replacing both RT-328T's with newish MX-300's I bought on
ebay, net cost after selling the cores was about $1100 for both units,
but this was perhaps an unusually good deal. If I had the $$$ I would
go the GPS/Com route, but *I* honestly don't need the capability right
now, I don't fly regularly anywhere that's only served by a GPS
approach, and cross-country flight around here usually means terrain
where the airways represent the only sane route in IMC anyway. But if
you fly over to grandma's every Sunday and the airport only has a GPS
approach, the cost/benefit equation changes significantly, no doubt
about it.

Martin