If it is less than it was previously then something could have been damaged when it was repaired. There are some very fine wires that run from the wireless card up to the antenna behind the screen. Although the wires could have been damaged the most common cause is that they are not tightly connected to the wireless card. They are very small and it gets tricky to get them back in place sometime. If you can get to the wireless card without completely disassembling the PC it may be worth checking it.
Other than that as stated above there are difference between how PC display the signal level. You never really know what a BAR means, some manufactures may pretend they have more signal just so people think it is a better device to buy.