When I first received the unit I found that it would not fire reliably on my M5 which is very bad for a family Christmas shoot (the family keeps looking at me critically and saying, that I could use my phone) oh! I was messing around with him and he started shooting so I finally got shots. Looking at it the next day I found that once it's locked I can lose the ttl-a indicator by sliding the flash into the hot shoe. I found the grounding to be inadequate and intermittent. Grounding between the camera and the flash is via two pins in the side groove of the flash, which must make contact with bare metal on the inside edges of the camera's hot shoe. With my camera, the side contacts of the flash slipped past the exposed areas and partially landed on the painted part. I scraped off another 1/16 inch of paint on each side and now I can wiggle with the flash locked and not lose TTL.
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