I'll try to give you a few tips before I leave the house.
IF this is the spindle controller I'm thinking of, you have an Asian-made CNC kneemill which unfortunately (or not) I've had experience "fixing" many times.
But first, if you can give as much info as possible, it will be easier.
If you have the Frequol booklet AND the programming device that plugs in the front of the unit that allows you to change the parameters, you are going to be fine.
If you don't - you can forget the rest of this post and you will not be happy.
The programming unit is about the size of a large remote control and isn't cheap. It will allow you to change acceleration and deceleration times of your spindle, max RPMs, the rpm's that it shifts from hi to lo gear, etc.
The most common problem is accel and decel time. If it is too short (less than 5 seconds) that usually triggers an over current alarm due to regenerative braking.
The solution is to change the parameter from say 2 or 3 seconds to 5 (or more if needed) to allow the spindle time to get up to speed and to stop.
The little manual that comes with it explains all this and you must have the programming unit to change these parameters.
Don't know if this helps, but it's all I got.