Hammer Drills - Page 2 - Recent Questions, Troubleshooting & Support

It is very likely the carbon brushes that contact the motor to transfer electricity to the windings. those tend to crack and get stuck or wear out. They need to be moving in and out freely and have spring pressure pushing them in towards the motor. you can get new ones cheap at ereplacementparts.com if they sell them.

Use the hammer drill setting. you MUST use a carbide bit.

no fuse in the unit check for broken wires in the plug or lead or faulty nswitch

check and test selector switch or hammering unit has failed or seized

replace the chuck

hi you need to dismantle the unit blow out all dust and so on insure the fun is ok and bearings

https://www.boss.info/global/support/by_product/dr-670/owners_manuals/70de05ce-4883-4236-86c8-509e1b6c2d60/ Owners Manual for DR670 Drill

Go to mfg web site for parts.

Hold the chuck with a strap or pipe wrench and operate the drill in reverse.

turn the lever from drill to hammer there will be 2 levers so follow the icons near the lever

Buy Hitachi DH40MR 1 9 16 SDS MAX Electric Rotary Hammer Parts Re4move the retaining screw #90 and remove and replace brushes

http://manuals.harborfreight.com/manuals/94000-94999/94436.pdf The link above is for the manual. There is a phone number at the bottom of some of the pages for technical assistance. Harbor Freight tools are sometimes difficult to get parts for. Either that or you can take the drill to a small tools repair shop and see if they can match the brushes up.