Hey, I’m trying to repair my first-gen Sigma 24–70mm f/2.8 DG DN Art (A019), and I’ve got stuck partway through disassembly.
The original fault was a hard zoom stop at around 40mm, before I opened anything. The zoom ring is now removed and the rear is open, but I can’t get the remaining outer housing off.
The odd part is that it slides a short distance backwards towards the camera mount, then hits a solid stop. How far it slides depends on the internal zoom position: the further I zoom in, the less the housing can move backwards.
It feels like it’s catching on something that moves with the zoom, but I can’t see where. The switch assembly and ribbon cables are clear. I also tried removing the three accessible screws beneath the focus ring; that made no difference, so they’re back in place. The front element is still installed.
I’ve been following a photo teardown, but haven’t figured out what’s retaining it at this point.
Has anyone worked inside this model, or seen a similar zoom jam also prevent the outer housing from coming off? I’d really appreciate a pointer on what to inspect or which part might be involved.
I know this is a complicated repair, but I’d like to understand the mechanism and try to finish it myself.
The photos show how far the lens is in rest, how far off i can get it, and how far i can get it after have zoomed. Last pic shows all disassembled parts so far.
Thanks!