Car radio query

Nov 14 04:53 UTC 2000

This is the sort of question Car Talk gets.  Of course, calling Car Talk,
you might have about a 1 in 500 chance of getting through, so I'll post
the question here instead. 

I have a 1997 Mercury Sable station wagon -- essentially the same thing as
a Ford Taurus. 

Recently, I started the car, turned on the radio, and discovered that the
preset radio stations had ALL changed.  Of course, this is not the old
style radio where the presets were done mechanically, but an electronic
system.  Most of them changed to within a few frequencies of where they
were, but one of them was "across the dial" (of course, there is no actual
dial, just an LED display). 

Some of them were changed to other stations; some of them were changed to
empty channels.  It seemed kind of random. 

This affected the FM stations, which ordinarily are the only ones I listen
to.  The AM presets are probably the ones the car had when we bought it; I
have no way of knowing whether those changed or not. 

Is this a typical sort of electronic glitch that happens to 4-year-old
Fords, or should I wonder if someone got into my car and changed all the
radio presets?

response 2 of 19:

Nov 14 05:01 UTC 2000

  I'm not sure whether the channel settings would be stored in non-volatile
  memory of some sort, but my first suspicion would be that the radio 
  temporarily lost power long enough for it to lose its memorized settings
  (e.g. from a faulty fuse or other electrical problem..) and the next time
  it powered up it had reverted to its factory defaults.

  Were the station settings it had switched to numerically sorted from
  leftmost button to rightmost?  That would seem to be a dead givaway,
  especially if they were also somewhat uniformly distributed across the
  FM spectrum.

response 4 of 19:

Nov 14 05:12 UTC 2000

If I remember right, the radios in the Sables actually have 2 sets of FM 
presets.  You've probably already tried this, but try pushing the FM 
button once more and see if that restores yours.

response 6 of 19:

Nov 14 06:47 UTC 2000

Is this really a car talk type question today?  My general experience
with auto mechanics in general has been that if it deals with
electronics, their competence just ended.  My expectation would be that
if it lost power, it would lose *all* its presets, and wouldn't have any
at all.  It sounds to me more like the power went low, but not entirely
off, and the radio lost some of the bits for the presets - from the
sounds of it, mostly the low lorder bits.  Another possibility is that
the radio got a glitch (EMI interference from visiting an airport?
Faulty ignition?), crashed, scribbled over some of its memory, and hence
clobbered its presets.

In any case, I'd definitely check the battery, especially if it's never
been replaced or serviced.  4 years would be about right for it to start
failing, especially now that the weather is getting colder.

response 8 of 19:

Nov 14 20:27 UTC 2000

It takes a God-awful amount of juice to run the starter motor, compared to
anything else on the car. If the battery was too weak to hold the presets,
the car wouldn't start. Starting it *does* reduce the overall system voltage
during the startup; but this is a regular occurance for which one would expect
the radio to be designed.

response 10 of 19:

Nov 15 03:26 UTC 2000

Small frequency jumps would be due to lesser significant bits being jumbled
while larger frequency jumps would be higher significant bits being bungled.
A preset is nothing more that a digital word stored away in an electrically
backed up RAM.  When you hit the preset button the given word is presented
to the PLL.  Anything that would cause bits to wander in a computer could
cause them to wander in a digital car radio.  It could also be that the
reference crystal that the PLL is synced to drifted a little bit.  However,
I don't think that would explain the big jump you saw on one of the presets.
Could be that the high sunspot activity diddled the presets or, perhaps,
your car was exposed to a high EMI environment ;-)

response 12 of 19:

Nov 15 04:55 UTC 2000

Wasn't there a solar storm recently?

response 14 of 19:

Nov 15 09:09 UTC 2000

My 1985 Ford Lincoln towncar will not.  Go figure.

response 16 of 19:

Nov 15 19:45 UTC 2000

Re #8: Could be the voltage dip from the starter scrambled the presets, if
the battery was low.  Or it could just be random.  My 2m rig will, about
once every six months, dump its presets for no apparent reason.

And bdh, I dunno about your '85 Town Car, but my '85 Crown Victoria had
*mechanical* presets.  I'd certainly hope starting the car wouldn't scramble
those. ;>  (The Crown Vic did have the absolute worst alternator whine
problem I've ever heard.  Electric fuel pump noise, too.  AM reception was
futile in that car with the engine running.)

response 18 of 19:

Nov 15 21:58 UTC 2000

That's an odd design.  The radios I've played with had a single ground lead
for both power sources, and the antenna lead was only a ground for the
antenna.