Clipper will only work on slow speed could it be circuit board

oops, you may have blown the circuit board or possibly the motor either way its not going to be a cheep fix. 120v clippers are not ment for 240V

Maintenance must be done and clean the engine

It sounds like a faulty motor if they are under a year old send then back who you purchased them from otherwise it could be a costly repair.
Dog Clippers

Let Oster sort it out under guarantee. If you mess about you are likely to kill the guarantee.

You need to replace the motor and the PCB. The motor is drawing too much current, that's what has wrecked the PCB. If the armature is a separate available part rather than a complete motor then it will be the armature you need.

The drive arm is probably not aligned with the corresponding opening in the balde. You have to close the blade against the clipper body with the clipper turned on. This should take care of your problem.

ok you need to take the upper cassing off, remove the hinge assembly and the circuit board now the motor unit should come away from the lower cassing.
remove the clips holding the carbon brushes in place beware there are springs behind these clips, remove the two long black clips holding the front and rear motor frames to the field coil and then pull apart. This will allow access to the armature and then simply unscrew the drive cam.
Totaly dismantle all the parts of your Andis AGC clipper.

OK AS FAR AS OIL YOU CAN OIL THE BLADES, AND ON THE SIDE OF THE CLIPPERS THERE IS A STRAIGHT SLOT TENSION SCREW TURN IT ON AND ADJUST THE SCREW TO THE PROPER SOUND AND FEEL THEN THE MOTOR WILL SLOW DOWN AND NOT GET SO HOT SO QUICK. I HOPE THIS HELPS.

IF THIS DOES HELP CAN YOU RATE MY ANSWER?
(I GUESS IT IS IMPORTANT FOR THIS SITE)

The intermitent system works off a circuit board which can not be tested by your means of your question. If the high & low speeds works fine the board is bad and should be replaced if sold separately from Chrysler