Rob,
Are you talking about EQMOD?
There are (at least) two types of USB to Serial cables -
For EQMOD you need USB to Serial TTL. This cable plugs direct into the EQ5 pro/EQ6 mount instead of the Synscan hand controller
This is different to the USB to serial you plug into the bottom of the handcontroller. For that I bought a Keyspan usb-serial adapter and it works well.
If you are looking for USB-Serial TTL try this guy:
http://www.dontronics-shop.com
The part is:
FTDI USB TO SERIAL (TTL LEVEL 5V) CONVERTER CABLE #16493
You will need to change the plug on the end of the cable to suit your mount.
Here is the link to the EQMOD site that explains what you need to do...
http://eq-mod.sourceforge.net/prereq...html#interface
Peter