charnwood w821 mini wood lathe motor problem

[sbt123]

hi there,im having a look at repairing a wood lathe for my dad,(charnwood w821)the problem is when turning up the variable speed control,the motor starts to stop and start by itself,if i continue to turn up the speed it will trip the mcb in the consumer unit,there is also a slight smell of burning from the speed controll box.,Another strange symptom is the lathe can be unplugged from the mains after switching it off and the motor will spin a couple of times by itself,so far ive put a new speed controll potentiometer on and new motor brushes,ive also tested the motor windings and everything looks ok with the motor.i can post more pictures of the speed controll box if required.
Thank you.

[stj]

the motor moves with the power off because of the energy stored in the big capacitor - so we know thats good!
does the motor spin freely by hand? good bearings?

[sbt123]

Thank you for your reply,heres a video of what the lathe is doing,.please note this is not the same make or model of lathe i have,,but the symptoms are exactly the same,also i have checked bearing which all seem ok,and you can spin the motor freely,i also have noted that the motor does not get hot after the power trips not even slightly warm.
Any idea why this mini lathe motor pulses like this? Is there a fix? : r/Tools

[stj]

i would get the board out for a good cleaning and inspection.
check for bad solder joints and replace any small caps