I tried blowing out the switch, but I'm still have the problem of the scroll saw speeding up and breaking the blade.
I also email Dewalt for help and this is the response I received from them.
"Hi Daniel,
Thank you for contacting us.
I apologize for the issues that you have experienced with your DW788. Unfortunately I would not be able to diagnose the issue with your foot pedal. We do not currently offer this accessory type and have not tested the DW788 for compatibility with third party accessories. I would recommend contacting the manufacturer of the foot pedal for assistance.
In case this email does not fully answer your question, or you would like to contact us for any reason, simply reply to this email.
Thank you,
Nathan
DEWALT Customer Care"
Hope some may have some other idea to fix this problem.
Thanks