IBM 5153 - Power-Up
When the IBM 5153 is powered on (including front-panel power switch), and it is not plugged into a video card, then you should see what is pictured below:
1. Green power LED is on.
2. Bright white raster. (Well, close to white.)
Note that seeing that is not an indicator that your 5153 is fully functional. To prove full functionality, you would need to plug the 5153 into a suitable video card (CGA), then run suitable video tests.