i replace the 3amp fuse with one 15 amp i think the 24 volts burn cause was smoking and sparkling,my question is i need to replace the whole board or just the transformer the ac star and with off and about 30 seconds after that is nothing

Please don't take this the wrong way, but the lack of punctuation, capitalization and run-on nature of your description, I am having trouble decipher the situation. I know folks are in a hurry these day, but please note the detail other posters provlde.

From what I can tell you swapped in a fuse without following the rule to check why it blew in the first place. The only way to know for sure what fried is to break out a voltmeter and check your transformer, and if bad replace that first. Next you will have to look at the board.

It sounds to me as if the magic smoke has escaped for the unit. Once the smoke has escaped it usually means you will be replacing some very expensive parts. To prevent this in the future take all necessary steps to insure that the magic smoke does not come out again or you will be replacing the parts again that you just replaced before. On second thought you might be safer financially if you called in someone that knows what they are doing to have an on site look at the problem since it is usually cheaper to do this in the long run.

There is another saying where the "semiconductor blue to protect the fuse" because the semiconductor is a faster device.

In your case, the PC trace on the board likely vaporized to protect the transformer because it's the lowest rated part because of the 15 Amp fuse.

There is a tendency now, not to LET consumers replace fuses with ones rated higher than they are supposed to be. Circuit breakers exist in homes for that very reason. Most consumers are scared to replace them. It's a good thing.