The altitude of my transponder transmission shows a red cross in the ACD-57

1) ON Mode:

In ‘ON Mode’ (also ALT INHIBIT), the altitude is intentionally not transmitted, and a red cross appears instead of the transmitted altitude. You can enter ‘ON Mode’ by pressing and holding the MDE softkey (on the XPDR page). If you want to return to the usual ‘ALT’ mode, press and hold the MDE softkey again.

2) Alticoder settings:

The alticoder in the VT-01 may be set incorrectly. If this is the case, a red cross will appear in the ACD-57 (FL display) instead of the transmitted altitude. 

In this case, please change the following: 

• PIN CODE 3000
• MENU > XPDR SYSTEM > INSTALLATION > XPDR CONFIG > ALT SOURCE please change to "DATA BUS".

After that, the altitude will be displayed, and the red cross should disappear.