nanoBTS Calibration

Hi guys, how do we calibrate the internal ocilator of the nanoBTS? I have a 139 unit which has synced up fine and has a olid green light but the network no longer appears on the handsets selection menu (the handset is dual band and the BTS is on an AFRCN within the handsets range). It was working before but the unit has been powered down for several months and I remember someone from ip.access advising that the internal oscillator needs to be re-calibrated to fix this issue.