Rear facing camera does not produce image

I replaced the volume control cable and battery, and afterwards the rear facing camera produced just all black on screen. As a next step, I bought and replaced the camera. I was very careful to study all the ribbon placements, and I believe all the connectors are in place. Sometimes you can capture a picture of the black screen, sometimes you can activate flash, but most of the time the shutter button does nothing, as though taking long time exposure. Replacement camera acted same way. Pulled apart and reassembled one more time. Same results - Anyone know if damage to logic board can cause this symptom, or seen this behavior? Everything else on the phone is fine now.