I repaired a 7d for somebody (a faulty rotary switch, and a general internal cleaning, with glueing the flying screw, which was of course on the side of the shutter motor), and after assembling it I checked the general functions of the camera.
And I have found, that the flash makes always overexposed photos, and there is no preflash possible (you know, that one which you can trigger with the “*” button. OK, I disassembled it again. No sign of any damage or fault. Assembled again – no preflash. Hrrrrrrr.
As the camera has been purchased recently as a used one, I was on the limit to give it back to the owner, mentioning that the camera has this small deficiency – but then i started to go through the menu – and i have found of course,that on these cameras there is possible to set E-TTL or manual flash, with different flash intensities, etc. Ouups. OK, I made the basic setup – and the flash was ok again….
The relevant information from user manual of the 7d
But what about the 40d?
The 40d has the same Menu item – but is greyed out!
So on the 40d it is not possible to set up the flash. Just on or off.
Note: RTFM means https://en.wikipedia.org/wiki/RTFM