BINGO .....

Yesterday I have made a test with my GpsMap 276C in my boat, using my
laptop and Hyperterminal. My Map 276C was taking 12 satellites and
running normal until I have made the test, and I have get exactly the
same results you have with your 172C. My position here (Salvador-
Bahia-Brazil) is S 12 48 W038 27 and thus GMT – 3.

The test showed:
a)The 276C was sending NMEA messages normally until 08:59 LCL (23:59
GMT) after that, it begin to send invalid NMEA messages like you
said, and little time after, stopped sending anything, see below a
small sample:

$GPRMC,235959,A,1248.705,S,03827.579,W,0.0,192.2,1 80207,23.0,W,A*3A
$GPRMB,A,0.04,L,AIC,BA01,1248.413,S,03827.698,W,0. 315,338.3,,V,A*3B
$GPGGA,235959,1248.705,S,03827.579,W,1,12,0.8,4.2, M,-10.5,M,,*60
$GPGLL,1248.705,S,03827.579,W,235959,A,A*41
$GPBOD,345.6,T,8.6,M,BA01,AIC*04
$GPBWC,235959,1248.413,S,03827.698,W,338.3,T,1.4,M ,0.315,N,BA01,A*6B
$GPVTG,192.2,T,215.2,M,0.0,N,0.0,K,A*2F
$GPXTE,A,A,0.04,L,N,A*07
$GPAPB,A,A,0.04,L,N,V,V,8.6,M,BA01,1.4,M,1.4,M,A*5 E
==================== = 23:59 GMT
$GPRMC,000002,V,,,,,,,,,,N*51
$GPRMB,V,,,,,,,,,,,,,N*52
$GPRMC,000006,V,,,,,,,,,,N*55
$GPRMB,V,,,,,,,,,,,,,N*52
$GPRMC,000010,V,,,,,,,,,,N*52
$GPRMB,V,,,,,,,,,,,,,N*52
$GPRMC,000014,V,,,,,,,,,,N*56
$GPRMB,V,,,,,,,,,,,,,N*52
$GPRMC,000018,V,,,,,,,,,,N*5A
$GPRMB,V,,,,,,,,,,,,,N*52

b)Around 09:08 LCL (00:08 GMT) the 276C started to send NMEA messages
normally, see the sample below.

$GPRMC,000134,V,,,,,,,,,,N*55
$GPRMB,V,,,,,,,,,,,,,N*52
$GPRMC,000138,V,,,,,,,,,,N*59
$GPRMB,V,,,,,,,,,,,,,N*52
$GPRMC,000142,V,,,,,,,,,,N*54
$GPRMB,V,,,,,,,,,,,,,N*52
$GPRMC,000146,V,,,,,,,,,,N*50
$GPRMB,V,,,,,,,,,,,,,N*52
$GPRMC,000150,V,,,,,,,,,,N*57
$GPRMB,V,,,,,,,,,,,,,N*52
$GPRMC,000154,V,,,,,,,,,,N*53
$GPRMB,V,,,,,,,,,,,,,N*52
$GPRMC,000158,V,,,,,,,,,,N*5F
$GPRMB,V,,,,,,,,,,,,,N*52
============== 00:08 GMT
$GPRMC,000833,A,1248.705,S,03827.579,W,0.0,192.2,1 90207,23.0,W,A*32
$GPRMB,A,0.04,L,AIC,BA01,1248.413,S,03827.698,W,0. 315,338.3,,V,A*3B
$GPGGA,000833,1248.705,S,03827.579,W,1,12,0.8,4.8, M,-10.5,M,,*63
$GPGLL,1248.705,S,03827.579,W,000833,A,A*48
$GPBOD,345.6,T,8.6,M,BA01,AIC*04
$GPBWC,000833,1248.413,S,03827.698,W,338.3,T,1.4,M ,0.315,N,BA01,A*62
$GPVTG,192.2,T,215.2,M,0.0,N,0.0,K,A*2F
$GPXTE,A,A,0.04,L,N,A*07
$GPAPB,A,A,0.04,L,N,V,V,8.6,M,BA01,1.4,M,1.4,M,A*5 E



Conclusions:

1)The problem is widespread like you and I have suspected, and
comproved in garmins 172C and 276C. What other models have this
problem?
2)As the 172C last update was in May/2006 and the last update
(software version 4.8) of 276C was much more recent in Jan/2007, the
suspicion of a widespread problem is very probable.
3)The time of day of the problem 23:59-00:08 is documented; could be
that there is another times when the error appears?
4)I will send warning messages by e-mail to all people I know that
sail using gps and autopilot.
5)I will open a new problem report with Garmin, regarding my 276C


I suggest that other people using these Garmin gps models and other
models too, do the test and open problem with garmin, since I repute
this problem a very high risk issue. Here in Bahia, almost all sailors
have Garmin Gps units interfaced with Raymarine Autopilots and we uses
extensively this interface, about 95% of time, specially when sailing
tricky routes, in narrow channels in bad weather or at night.

Congratulations John, thanks for your advise and best regards

Pascal Goncalves

S 13 00 W 038 27
Salvador – Bahia - Brazil