A500 replacement FDD

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Probably FDD 'heads' are misaligned, there is software on aminet to 'fine tune' them; but its pretty difficult since it needs to be done with high precision. Its doable, just needs patience/time. Have you tried repairing/cleaning the FDD that wrote floppies?

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BTW, are you the Daniele Gratteri from comp.sys.amiga.hardware?

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then replace A1200 FDD

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sorry it didn't work;
do you have X-Copy or D-Copy? you can use them to check if diskettes contain readable tracks. (try making copies with them)
maybe A500 has damaged CIA or something..   :-?

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AFAIK, if you get all green 0 with x-copy then everything is fine.
It can only be compatibility then, what kickstart do you have in A500? How much memory, is it slowfast, what games are you trying?

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that small company is probably selling modified PC floppys and you can easily do that by yourself, just swap few wires and add diode (instructions are on aminet)