Kejian KGH-6380C phone only move cards, and dropped when the signal is a bit poor. Unicom card capacity is used to search, showed a "limited service", dial the phone cannot be (search for network failure). This machine after startup, call "112" (no cards) normal and hit the mobile card, normal, but less will signal search network failure; with Unicom card, you cannot search network, nor can call "112". View the network settings, is no exception, cell phone signal bars display and is normal. When there is no card can call "112", stating that receiving circuit properly, the problem may be in transmitting circuit. Network manually in the menu search, Unicom and mobile networks can be found, but registration, Unicom card fails, also illustrates the transmitting circuit has a problem. The machine is a dual-band mobile company in 900MHz (GSM) and 1800MHz (DCS) are transmitting signals, while China Unicom is currently available in 900MHz (GSM) signal. The unit may have failed. Kejian KGH-6380C has two transmitting channels, 900MHz, and 1800MHz processing the signals and transmitted respectively. Transmission circuit problem, amp damage most likely. Power measuring power amplifier 3.6V power supply PF01411B and PF0414HB 8 foot, 1 normal transmit signal feet 1800MHz power amplifier inputs, and 900MHz amplifiers 1 foot did not 890MHz~915MHz signal input, signal outages. Forward search, finally found 900MHz voltage controlled oscillator (9P7-897) is damaged. After the replacement, Unicom card is available, move the card when poor signal does not come off the line. Fault damage is causing the phones optional card 900MHz channel.bX4service manual download site