If you have a huge pulse sound then you turn off your motif or distorted signal to the main outputs. Check for DC voltage with voltmeter and an unconnected cable from Tip to Sleeve. If you found around 1,5 volts or 2,5 volts, your muting transistors are damaged and output is leaky.
The muting transistor is intended to prevent the popping of loudspeakers when power is applied. Obviously, the function of muting circuits is to mute (kill) the audio signal.
The muting transistor of Motif XF is the Toshiba 2SC3326 :
I suspect that a regular disconnection of the jacks while my Motif was switched On or a phantom power + 48V sent by a sound mixer, had caused the failure. So Turn Off your Synthesizer when you want disconnect the output jacks, This can lead to overvoltages while making connections. And Use often a D.I box on stage to prevent a phantom power.
I disassembled my Motif , is brought the JA Circuit Board WU494900 to a friend Electronics Technician who after having ordered the transistors (sold by 10) realized the CMS desoldering/soldering.
My Motif works fine now : full dynamic, no pop up or cracked sound and no DC voltage on line output.
To enter on Test Mode : Turn on the power while simultaneously pressing the [REMOTE] and [ ] (REC) buttons until the “MOTIF XF” is displayed on the screen and release the buttons. You have 6 Test programs for output signal : 1000Hz at -12dB, -6db and 0db Left or Right.