Logic probe during solenoid test will quickly show if the decoder is ok. These pulses are slow enough a DMM on volts DC is fast enough. Make sure all inputs from the MPU reach the decoder chip A B C D pins. Basically make sure each ones changes state at points during solenoid test. If it is always 5v, then the connector for that signal is likely bad somewhere between the MPU and driver.
If I would guess driver J4 has cracked solder joints based on my history. The decoder very rarely fails, even when solenoid transistor burn holes in the board.