Further what would happen if one would connect a NTSC A520 into a PAL amiga or visa versa.
I haven't tried it, but from what other people say it only affects the colour encoding on the composite out & the standard of the RF out.
If you use a PAL A520 on an NTSC Amiga then the output will be what we call PAL60. If you use the wrong one for your monitor then the display will be black and white. If your monitor can't cope with the refresh rate then it will roll, although even then some monitors can be adjusted if they have a vertical hold control.
I assume an NTSC A520 on a PAL Amiga will create NTSC50, quite how well that will be supported by TV's I don't know. Support for PAL60 is relatively common in europe, some modern games consoles output it.
Some (not sure if all) PAL A520's have a PAL standard selection switch as there are multiple audio carriers in use. There is also supposedly a different part number, but I can't find a list. If you open them up then the clock crystals are different values.
FWIW PAL and NTSC only refer to the modulator, although we refer to the A500 as PAL or NTSC it's really just 50 or 60hz (and even that can be configured using a jumper on some Amigas).
