If the LCD does not turn on when you turn the power on, first check your power cable and ensure that you are getting power to the printer. Next, check the RAMBO board behind the LCD to see if there is a solid green LED are lit up. (A blinking yellow LED does not indicate power, it indicates there is attempted communication between the computer and the RAMBo.)
If the LCD is not illuminated and there is not a solid green LED illuminated, you have likely blown the fuse in the F3 position on the RAMBO board. This is the fuse that controls logic for the board, without a functioning fuse you will not have a working RAMBO.
- You shorted the hot end when working on it with the power on. (always turn the power off before working on the hot end.)
- You may have a fan wire or hot end lead making contact with something that it shouldn't be.
Here is a diagram of the board layout and fuses: RAMBO Fuse Diagram
Here is where you can source replacement fuses: Ultimachine
You will definitely want to find the source of problem whether it is a short or it was self inflicted to prevent the fuse from blowing again.