FIXING GARMIN'S 90 KNOT SPEED LIMIT

We don't recommend trying to modify your GPS unless you have experience
soldering surface mount components, have access to a good EPROM programmer,
and are willing to break the waterproof seal on your GPS.  

Here is the surface mount part that contains the firmware:
  ATMEL	AT27LV020 32pin surface mount 3.3V 256k x 8 (2Mbit) EPROM 

Here is a report from Tim:

----------------------------------------------------------------------------

In the GPS45 code I see something like:

	if(numberA>18000.0)
		3dsatus=off;
	if(numberA<-1200.0)
		3dsatus=off;
	if(numberB>514.0)
		3dsatus=off;
	if(numberB>46.3011)
		3dsatus=off;

18,000 meters is 59,055 ft.		[maximum altitude limit]
46.3011meters/sec is 90.00213 knots	[infamous 90 knot limit]
514 meters/sec is 999.13 knots		[otherwise limited to 999 knots]
-1200 meters is -3937 ft		[perhaps Garmin uses this limit to
					discard a bogus datapoint]

----------------------------------------------------------------------------

The speed limit is 46.3011016846m/s.  If this number is changed, the
GPS45 will work above 90kts.  The value in the rom is a standard Intel
format single floating point value of 0x54343942 and in Ver 2.41 is located
at 0x3FBD8.

A few words of caution.  This has been attempted by a few people and I
only know of one almost good success.  I fixed two GPS45 and one has
no display and the other is losing columns in it's display.  

In order to make this change you need:

1) surface mount soldering station,
2) a steady hand 
3) eprom programmer that can program 20 pin TSOP packages and 
4) A microscope unless your eyes are better than mine.

You will have to disassemble the unit and remove the backlight
as well as the antenna and then remove the rom.  Getting this far may
break things.