A while ago I purchased a shoestring astronomy GPINT parallel port auto guiding connector and made up a custom cable. I noticed some strange behaviour on my CG5 and here's why and more importantly how to fix it.
The problem is if you leave the GPINT's autoguiding cable permanently attached, then the mount can wander some when you are not autoguiding!
Why? Well upon start-up Windows doesn't initialise any defined starting state for your parallel port's data lines. So whatever random state the data lines are in this gets continually broadcast along the parallel port and it moves your mount steadily away from wherever you might wish to be!
I checked with Shoestring last week, Doug Anderson informed me that only their USB autoguiding adapter covers this by defaulting all lines to 0 - no signal on boot, so there is no issue there.
Here's a simple fix, cause otherwise its quite involved initialising a Parallel Port under some versions of Windows.
1. Download a freeware Hex editor
2. Use it to create a file called empty.bin
3. Insert just hex 00 (a null) into empty.bin and save it to a prefered location
4. Use notepad to create a batch command file called clear_auto_guider.bat
5. In this file write (without the quotes) "copy /b c:\empty.bin LPT1"
6. Under Control Panel -> Schedule Tasks create a new task that runs clear_autoguider upon boot up
Problem should be solved! What this does is send a null to the parallel port, which then gets remembered so it sets the Port's data lines to zero - no movement!
