IBM 4820 System Reference Manual page 105

Condition description
Unsupported video mode
No Video/DPMS
Troubleshooting common problems
Resolution
Display Messages for Models 46x, 42x, 4Fx
Change to a supported model.
Communication is not yet established between
the host unit and the 4820. Ensure that the
4694 system unit is powered on. Check the
video cabling between the 4820 display and the
4694 system unit.
Appendix B. Troubleshooting common problems
B-5