So I removed a clicking drive and unrecognized from my old Imac, wd2500, bought a donor board and replaced the u12 rom . But now the drive is completely dead. What could I have done wrong? Is there a direction for the U12 ? Could I have place it up side down?

thanks for your help

Yes, there's a side, there's a little dot on the chip. Best is to get a ROM reader and save the content before moving the ROM.

What tools have you used to swap rom?
What temperature have you used and how long have you exposed the chip at heat?
Do you have a microscope to see if you really soldered it properly?

It's possible that the rom chip pins are not soldered well on pads, noobs often can align chip vertically and horizontally only, but they don't pay attention to hight (expecially when using hot air).
If you watch with a proper angle under microscope you will see if pins are touching pads or if they only brush them. If you're using hot air then you should use tweezers to push down the chip while tinned pads are melted. Keep holding down the chip until pads cool down.
I suggest to use a bit of flux to eliminate oxidation that does not allow you to make good welds. Amtech produce some good flux, one of the most used is the Amtech NC-559.

It's also possible that you have killed the chip rom for overheating or for having soldered in the wrong direction or due to tinned bridges (shorts) on adjiacent pins.

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My firmware database:
https://mega.nz/folder/O01DkBRI#MxP2J6ZNqXDcrX40I8MoQQ

thanks for your answers. I have use a hot gun and magnifier. But the solder is very limited.