Hello gurus, please I have a Yamaha Montage 8 Keyboard that whenever it’s power on it fluctuates, sometimes the screen flickered and later shut down.
Sometimes we have to power it on & off for about 3times before it get stable.
Please what could be the problem and possibly solution(s) to this.
Thank you for your quick response.
I’m most grateful.
Is the mains voltage stable? I have had similar issues (with different keyboards) when performing at outdoor festivals where the power was supplied by generators. A loud bass guitar note would cause the mains voltage to drop, which would drive my keyboards crazy. A Furman power conditioner (that put out a steady voltage no matter what the incoming voltage was) cured the problem.
And if the mains is good it could just be a faulty switch or switch that needs cleaning. You can confirm this with with a meter in continuity mode (just measure resistance between the pin on the mains plug to the output pin on the switch. Do this with the synth not connected to the mains obviously 
Thanks you guys are the best.
I will carry out those examinations next time I’m with the Keyboard this week.
Thanks. Will update you guys on it.