Furuno NAVNET 1833 - Manual (Page 221)

7. MAINTENANCE, TROUBLESHOOTING
7-9
7.6.2 Test pattern
1. Press the [MENU] key to show the menu.
2. Press the SYSTEM CONFIGURATION soft key.
3. Press the SYSTEM SETUP soft key.
4. Press the TEST & CLEAR soft key.
5. Press the TEST PATTERN soft key to show the test pattern.
RETURN
Test patterns
6. Press the RETURN soft key.
7. Press the [MENU] key to close the menu.