Hi Phil,
You can view the drawings on the Dewalt website:
https://www.2helpu.com/products/HomePage.aspx?BrandId=2&language=en-GB&country=GB
They are pretty straightforward to repair, depending on the model.
If it is a combi drill - DW988, DC988 or DC 925, it is most likely to be either the brushes, easily replaceable, damaged switch to brush lead, easily replaceable, or the switch (most common)
The easy way to test is to first twist the torque setting to the minimum setting (to stop the gearbox from exploding when you take it off!!), then you can take out the 4 gearbox screws (Torx T10), then the rear cover, another 4 Torx T10, then carefully slide the gearbox out, with the front end and gearbox attached, then remove the rear cover, then remove the last 5 torx T10 screws from the body, check the brushes 1st, as these can be changed by just taking the back cover off(if they need changing, pull off the spade terminals, then put a small driver in at the front and prise them out, the new ones just slide back in).
The easy way to check is to disconnect the 2 wires from the switch, with only the motor connected, then put the 2 wires on to the battery terminal, keeping a hold of the motor, if it now works, it is the switch, if it dosen't, then it is most likely the brushes (which should have been checked 1st) as the motors rarely go wrong.
Whatever you do, do NOT take the gearbox apart, as this is a sealed unit, NOT designed to be taken apart, and is very difficult to put back together, if you have a fault in the gearbox - simply buy a new one!!!!
I hope this helps.
Dave the tool repairer, October 2007
