That chip appears to be hosed. Either the transmit-only pin 8 will be hot for transmit, or the receive-only pin 6 will be. But if both of them are zero, that's a bad sign. Pin 1 is the kicker. This should be a steady 8 Volts DC all the time, transmit and receive.
Might be wise to check the circuit board pad where pin 1 connects for a short to ground before trying a new MB3756 chip. For that matter, if you unsolder JUST pin 1 and see 8 Volts from the loose pin, that would suggest a short that's overloading the chip's output current. Sure don't want to overload and pop a
