I'm not familiar with your machine, BUT
... that description of symptom sounds suspiciously like
a bad/poor electrical connection.
The problem could be in many places
:
- plug
- cord
- switch
- brushes
- internal electrical wiring
The "solution" to this problem is for
someone who knows what s/he is doing, to troubleshoot the defective machine, determine the defect, and properly repair or replace the defective part.