You are likely getting all the NTSC lines. The problem is that NTSC has 525 lines and PAL has 625 lines, thus there are 100 blank lines when you convert NTSC to PAL. To fill those in you would need A/D conversion, an interpolation circuit, memory and D/A conversion, to generate the extra 100 lines from the NTSC signal, and that requires significantly extra circuitry that inexpensive home converters don't have. Expensive broadcast type converters probably do.