Here we have a DELL Inspiron 1564 laptop. The problem this laptop had, was that he has no sound on external speaker. As we see from outside, the speakers port (3.5mm) was broken, so we order a used sound board online.
When the board come, we see, that the one that we get is not completely the same as the one from the laptop. That’s why we try to use the plugs from the new board and solder it to the old sound board.
After that everything was working fine, but for a short time.
After a day or two the laptop don’t have a sound on external and built-in speakers as well.
We disassemble the laptop again and after a few measures, we concluded that the mosfets (that are assigned on the next picture) were faulty.
The MOSFETs on the original board was assigned as F1T, and the MOSFETs from the new board was assigned as K72, but the characteristics of this two MOSFETS are very simmilar as we check from manufacturers datasheets. so, we replace the MOSFETs and the sound was back again.