Dark Band at the bottom of photos

So I'm having an intermittent issue with my 1DmK3 for almost a year now -

When I'm doing studio shoots (f/5.6, 1/125, ISO100) I get a dark band across the bottom of the photo on like every 3rd photo or so -

Like I said this has happened on only SOME of my studio shoots going back a year or so.

At first I thought maybe the shutter was going but I figure it would have gone by now. If I slow down to 1/100 it doesn't happen.

What gives ?

I'm using a PW Mini and Flex TT5 to fire my AlienBees.

Lets see an example please.

My guess is that the PW mini isn't syncing correctly at the faster SS. Test out this hypothesis by using a PC cable to see if it still happens without the PW.

squashed wrote in post #16408071
Lets see an example please.

I won't be able to upload a photo until this evening - it's a dark band that gets lighter but concentrated to the bottom of the photo.

I'm thinking shutter speed also...

Camera has @ 50,000 clicks

I NEVER see this outdoors or with my 580EXII - ONLY in a studio setting and like I said maybe in 1 out of 20 photoshoots if that, and even then on every 3rd photo or so.

Sounds like shutter to flash sync issue to me too.

alexxn wrote in post #16408082
Camera has @ 50,000 clicks

I NEVER see this outdoors or with my 580EXII - ONLY in a studio setting and like I said maybe in 1 out of 20 photoshoots if that, and even then on every 3rd photo or so.

The disparity between ambient and flash is less so you wouldnt see it as much or at all outdoors even if its happening.

OK so is this something failing or a sync issue perhaps with the PW's ?

Most likely a sync issue, but yes.

gonzogolf wrote in post #16408164
Most likely a sync issue, but yes.

OK. I guess I can try one of the sync cables that came with the AlienBees next time and see what happens.

I'm wondering if it's not a bad idea to ditch the PW's all together and get some Buff Cyber Syncs instead.