If the back display is showing an image the CMOS sensor is working, when looking though the eyepiece withe the shutter set on a long exposure does the image go out (become dark) if that happens then you know the reflex mirror is moving out of the way, often times this is the failure.
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If the back display is showing an image the CMOS sensor is working, when looking though the eyepiece with the shutter set on a long exposure does the image go out (become dark) if that happens then you know the reflex mirror is moving out of the way, often times this is the failure.
That only leaves the mechanical shutter which sits in front of the sensor. This is used when the camera is taking high speed images like older film focal plane shutters to limit the exposure.
If the back display is showing an image the CMOS sensor is working, when looking though the eyepiece withe the shutter set on a long exposure does the image go out (become dark) if that happens then you know the reflex mirror is moving out of the way, often times this is the failure.
That only leaves the mechanical shutter which sits in front of the sensor. This is used when the camera is taking high speed images like older film focal plane shutters to limit the exposure.