Hello Bart,
As explained in the GTX330ES manual, the NO ADSB indication will appear in the upper left corner when ADS-B is configured on, but the unit cannot transmit the position of the aircraft or when ADS-B TX is manually turned off in normal mode.
This indication will always be present before the GNS has a GPS fix.
Information on software is
discussed here.
First, please recheck wiring and configuration to make sure the data is getting from the GNS to the GTX. Here are a few configuration setting to check. The items in blue, and of course the wiring, are most important to turning off the NO ADSB indication.
GNS/GTN
RS-232 Port Output: ADS-B Out+
GTX330ES
RS-232 Port Input Connected to GNS/GTN: Remote
GPS Integrity: 1E-7
ADS-B TX: Enabled
EHS: Enable
Let us know if you have additional questions.
Thanks,
Steve