On Nov 8, 2:56*pm, wrote:
One reason could be that there is a short in the temperature probe line. *See if it will boot up after you remove the temperature line. *The manual addresses this condition.

John

Another reason (also in the manual) is;

"B. The 302 LCD screen shows [300] [CAI] but nothing else.
Disconnect any devices on the “CAI Bus” such as the 303-NAV or 306 DDV
repeater. If the
302 is then OK, check cables and connectors. If the problem persists,
the DDV main
processor has failed. Return the instrument to your dealer for
service."

If you have a 303 (pretty common) or a 306 (rare) it could very well
be the cables. These use "phone" connectors (RJ). These are fairly
robust but in our bumpy environment get loose, corroded, etc,
especially when repeatedly removed/inserted. Disconnect and inspect
them. Replace where needed. If this is the case contact me and I can
make you what you need.