On 26-04-2015, at 2030 Hrs, the transmitter was tripped off due to power supply failure on both WAPDA feeders. After restoration of Power Supply, transmitter was put on but only one unit of the transmitters i.e. TX-A automatically connected to Antenna because of some fault in second unit i.e. TX-B. The entire system of the transmitter was checked and found that the output voltages of the AVR & PDB of TX-B were nil. In order to avoid lengthy breakdown, transmission was on aired using the single transmitter unit (TX-A) resulting in reduction of output power of the transmitter from 500 KW to 250 KW only. After close down of transmission, the AVR & PDB circuitry was checked thoroughly and noticed that the phase sequence / loss relay named/tagged as OPR (Open Phase Relay) was not functioning properly. As the spare relay was not available in store, therefore only one unit of transmitter was remained in operation and after purchasing & installing new relay, the entire system was taken in circuit in order to obtain full power of 500 kW.