Steps to fix GT-i9500 WiFi because the Wifi Icon lite is dim.

If you can't turn on wifi at all. Most likely the Wi-Fi IC needs to replaced. Not easily replaceable as it requires careful heating to a certain temperature to remove and replace. Better to take it to a phone repair shop that does this.

None of the flex cables that plug into the logic board would cause this.

This can be fixable by flashing system firmware and doing a wipe data / factory reset. If this doesn't work then it's definitely an hardware issue like I said above.

Steps to Factory Reset Samsung Tablet (You will lose all data on the tablet):

1. Turn tablet off
2. After that Boot your device into Recovery Mode. You can do this by holding the Volume Up + Home + Power keys. When the Samsung Logo pops up, stop holding the power button but keep holding the rest.
3. Once your android device is in Recovery Mode, Go to the “wipe data/factory reset” option and select it.
4. After that go back to the recovery main menu and reboot the device by “reboot system now” option.