The LCD screen is not lighting up.

@victordcon10720 that could be a backlight issue. Change the contrast settings and see if that brings the screen back. It might be time to change the CMOS battery. That will reset the backlight contrast to 0. Change the contrast settings and see if that brings the screen back.

A simple check for the backlight would be to darken the room and turn the EKG machine on. Then use a flashlight and angle the light at the screen on different areas. You should see the Splash screen when it first turns on or even an EKG tracing if you are acquiring one.

Check for a service manual for the 150c on the bottom of this page Mortara ELI 150c There should not be to much difference to get into the machine even so some of the internals may be different.

Once opened, check the keyboard cables as well as the LCD cable. Make sure that all of those make proper contact.