VOR Receiver

[Slaton]

I have a King 175B Navcom that works great except for the CDI, which works great
sometimes. When it works it is fine, when it doesn't work there is no life except if I
change frequencies then the "To - From" flags almost swing into position, just enough to
make me think that if I spin the frequency dial a few times it will clean up and save me
a trip to the shop. The other VOR receiver works like it is supposed to so I know that
the problem isn't some out of range fluke or something cheap. No problem with the Com
part or the Identification, etc. I am tempted to pull it and spray contact cleaner or
WD-40 or something on the "innerds" but that is not usually smart.

This is beginning to get under my skin, about the time I give up and call the shop for
an appointment it starts working and does just great untill I cancell the appointment.
I really hate to take an instrument to the shop when it's working great and tell them
"Well, sometimes'.

Any ideas? Speculation is encouraged. Leo

[Rod Farlee]

The nav ident works fine, so it's not the nav receiver or antenna. If
you have a strong audible ident, the tuner is OK.

The plug behind the #1 nav is the primary suspect. Pull the radio out,
spray the pins and plug with Radio Shack TV Tuner Spray Cleaner/Lube,
and reseat it a couple of times. Make sure it is seated completely into
the connector.

In the CDI, the OBS knob moves wipers around a large circular
wire-wound resistor. There are four wipers, which decode the bearing
dialed in by the OBS knob. If these contacts have oxidized, you'll get
erratic CDI readings. They can also be sprayed with tuner cleaner/lube.
Have to remove the CDI from the panel and open it's case to do that.
So I'd try the connectors first, especially as the erratic when you're
touching/pushing/tuning the radio, not the CDI.

An erratic problem is not one you want to turn over to the radio shop,
because it's hard for them to find and be certain they've fixed. The above
at least eliminates the usual suspects, and will often solve the problem
or help you isolate it to a bad connector which can be replaced.
- Rod Farlee

[sjm...@earthlink.net]

I have a slightly different problem with a Narco MK-12D. It is also
intermittant, sometimes it works perfectly, but then it starts to move off
left of course usually around 30 degrees, however I have seen it as much as
70 degrees off.

I took it to the radio shop couple months ago, and when they put it on the
bench it was indicating 70 deg off, when they opened the case it worked
perfectly, they shook it, and froze it for two days and it worked
perfectly, so they put back together, said it was probably just a lose
connection (charged me 100 bucks), and it worked great for the last two
months, untill last week when it started to act up again. I hate to take it
back to the shop again if it's still an intermittant problem.

Ident is good and strong, CDI swings nice, TO/FROM works, everything seems
normal except it indicates way off in left field occaisionally.

Any Advise?

[BZmans]

Leo.....some quick biased advice. If you have two 175 B's switch their
poosition and note if the problem moves with the radio. Sounds to me like you
have a problem in the converrter portion of the indicator. Now the biased
part(I work there)......send it to Dave Krant at JA Air
Center...Chicago.630-584-3200/800-323-5966. JA has installed and repaired more
170 series than anyone in the world. Quick and inexpensive repairs.

[Alan D. Wilcox]

FWIW ...

Narco card-edge connectors aren't too reliable (they're not
gold plated). Many times, removing the equip from rack and
spraying with electrical-contact cleaner (NOT WD-40!!) will
work wonders.

Some of my equipment that had internal cards + connectors
needed the same fix inside case as well.

Not saying this is a fix for your particular situation though.

Alan