After replacing screen the bluetooth doesn't work.

Hi all, I've repaired dozens of 4th gen touches and can tear one down and reassemble it nearly with my eyes closed but I'm baffled by this issue. On the last 4th gen I repaired, my customer is calling me and saying the Bluetooth on the device doesn't work. WiFi is fine but no Bluetooth. To be completely honest, I don't even know where the Bluetooth mechanism is located. Please help.