I have Canon 300D and need some disassembly procedure.

check lens aperture

Are you using the flash? if so then the shutter speed is not synchronized with the flash if no flash is being used then the shutter may need replacement.

Hard to believe that you took your camera apart without prior knowledge of what to do. Good luck.

That problem is normally associated with having a too high shutter speed when using flash. If it happens in any mode, with or without flash you may have a shutter blind issue.

Test the camera at various shutter speeds and compare the results. If this black area is consistant across different shutter speeds, send it in for repair. It is most likely the shutter curtain not making a pass across the sensor fast enough, still obscuring the sensor when a photo was taken.

This is fairly common on the 300D - the submirror ( underneath the main mirro ) has a plastic pin that breaks - the camera has to be disassembled to replace. Expect to pay an independent repair shop about $105 or from Canon $180.

Once the CF access door is open, just push the small square button that will be below the card. That moves it out enough to pull it out. When putting a different card in, take care not to just jam it in as you could bend the pins.

Your sentence is not making much sense.
Turn the dial in manual to change the shutter speed
Hold the AV button and turn the dial to change the aperture
You can then press the exposure button (*) to see if your settings are too dark or light before you take the shot.

Is this what you want?

I think the shutter broken.
Your problem is same me.
And now i need some disassembly procedure for replace it by my self.
The technician send, you can disassembly it from front of camera not from back to CMOS.
I only have disassembly procedure from back.
Are you have any disassembly guide from front of camera?

assuming you have the exposure set correctly (if u set way underexpose, the frame will appear black). Try put it in "Auto" mode and see if it works.

If it doesn't, your mirror mechanism may be faulty. One way to check is to take a photo of 2 seconds or longer. Look into the viewfinder, can you see anything through the viewfinder during these 2 seconds?

shutter mechanism of canon 300d lasts for around 5000 shots or less!! yes it is made of plastic materials thats why here in the philippines I am making my own metal replacement parts that lasts. Unfortunately, in your country you cant do anything but to replace it with same original replacement parts. avoid using faster shutter speed and continuous shots.