Figured out how to burn cartridges for the PCJr. The binary file for Cartridge basic floating around has some header message stuck to the start of the .bin. Once I figured that out I stumbled my way through a hex-editor and got it to work. Will post the fixed file on my SDF website
@SDF Thats a great link. My problem was I didn't know about "The two first bytes must be 0x55 and 0xAA.". Those carts are nicer then the ones I have. I think my are more of a clone of the originals.
https://www.ebay.com/itm/274235906214