Stuck chuck Chuck stuck on model EPC188

Use the chuck key to open the jaws of the chuck as wide as possible. Look down into the chuck and you will see a screw head. Use a screw driver to take this screw out BUT turn the screw CLOCKWISE as if you were tightening it as the bolt will have what is known as a left hand thread. With the screw bolt out put your key back on the chuck and using a wooden or rubber mallet give the key a tap as if to turn the whole chuck ANTI-CLOCKWISE. This should enable you to rotate the chuck off by hand. If it is still stuck give it a sharper tap.

Give it a shot of WD40 It may be stuck and seized up. Soak it inside chuck as well.

Can not see what model you have. Is it a keyless chuck or an SDS chuck? With a keyless chuck hold the machine in a vice by the drill bit. now tap the chuck with a hammer or pin punch & hammer. DONOT hit the chuck on the jaws gut on the rim around them. I have had success using this method. If it is an SDS type chuck pull the chuck cap up as far as possible along the bit them if there are any ring springs you will have to try remove them then slide the sleeve up the bit, now you should be able to remove any steel balls. If the bit does not come out now hold bit in vice as before and tap on tool holder.

If the chuck is stuck open and you cant "muscle" it closed something is probably jammed up in there and it needs to be replaced. Chucks take a good share of the abuse on power tools and most manufactuers consider them a "common wear item" like brake pads or Tires on your car. A chuck is fairly simple to replace if your drill stuck open and they are commonly replaced on the higher end "Industrial Grade" Power Tools like DeWalt and Milwaukee.
Looking at the Make and Model of your drill it would probably be easiest and most cost effective to just replace the entire drill. If you tried to replace the chuck and found a chuck that will fit your tool it may cost you anywhere from $25 - $40. For Around $40 you can purchase a new drill with a fresh battery.

By stuck do you mean that you can not release the chuck? if so then you can use 2 channel lock pliers to grip the chuck and the base to break it free. i have done the same on a keyed chuck and a keyless chuck .

That can happen if the jaws inside the chuck, usually 3 triangular pieces get jammed together. With chuck facing down tap chuck several times to loosen jaws. If that doesn't work spray a small amount of WD-40 into chuck and try again

I'd put penetrating oil in it and tap the chuck with a plastic hammer. That should free it up.

Best rgrds, W/D

if chuck is wide open ,look down inside there should be an allen screw or bolt at the bottom of the chuck it should undo anti clocwise and the chuck comes off

I looked at a old schematic for the 5078 and it appears that it might come off after chuck removed. The chuck is threaded and if you have the 2 speed model, shift it to low and put a bent handle allen wrench into the jaws and chuck on workbench or block of wood with long portion at approx 30 degree angle and strike the handle, you will be hitting it counter clockwise to remove.

You will find a screw inside the chuck that needs to come out first of all but beware that it will be a reverse thread. This is to stop it loosening whilst in use. then you will need to unscrew the chuck but it isn't easy as you have to hold the shaft that the chuck is attatched to. You can sometimes take the chuck off by holding it and pulling the trigger while in reverse. (but they can be stuck fast).