Can I safely access or disable the zoom lock on a Tamron 24-70mm f/2.8 Di VC/USD to free it from 24mm?

Question

My Tamron 24-70mm f/2.8 Di USD/VC zoom lock is stuck in the locked position, leaving the lens fixed at 24mm. The problem developed gradually: unlocking became harder each time until it stopped releasing altogether.

The lens is out of warranty and I need to use it before I can send it to a repairer. I’m not looking for a full teardown guide, but I’d like to know whether the zoom-lock mechanism is accessible with limited disassembly, and from which end of the lens that access is most likely to be possible. I understand the risks of opening a lens and want to avoid unnecessary disassembly or disturbing optical alignment if possible.

Has anyone worked on this lens, or a closely related version, enough to say whether the lock can be reached or removed relatively safely?

user27440 · Accepted Answer

Don't know exactly how useful this might be but Roger Cicala's lensrentals blog has comparison teardowns of the Canon, Nikon, and Tamron 24-70/2.8 lenses with lots of pictures.

Quoting the Tamron relevant text from that article:

Front Group

One thing that all 3 of these lenses have in common is a large front group at the end of an extending barrel. They all disassemble the same way – a makeup ring is removed exposing the screws that let us remove the front group from the lens.

...

Opening up the Back

For all 3 lenses, opening up the back involves removing the screws that hold the bayonet mount and electrical connections in place. ...

... We dissected a Canon-mount Tamron, so it doesn’t have a mechanical aperture lever. Had we done a Nikon-mount version then the bayonet mount would have had an aperture control lever, like the Nikon. Like Nikon, however, the Tamron (and most third-party lenses) use shims under the bayonet mount to achieve proper spacing.

I'd assume the A-mount is closer to the Canon in this regard.

... Under the shim, however, the Tamron has a PCB like the Canon. Older third-party lenses generally didn’t have PCBs, but in recent years most are using them. I particularly like Tamron’s because they are a very cool black color. I assume the plug with green marks on it is a computer connection for factory adjustments....

Removing the Rear Zoom Components

Once [its] PCB is removed, the Tamron shows some traits similar to both the Nikon and the Canon lenses. It doesn’t come apart modularly like a Canon, but it is a bit more organized inside than the Nikon. The aperture key ... need to be removed, along with 4 mounting screws, then the mid barrel comes off. ... The mid-barrel contains the Tamron’s GMR unit.

He also has a final section on how to make optical adjustments for the Tamron.

I'm guessing that once you can get the optical assemblies out of the barrel, you can access the back of the switch to see what might be physically broken, and hopefully find a way to jury-rig up a fix. But I'm not the type of girl who pulls her lenses apart. Her fountain pens, yes. But not her lenses. I took the back ring off my Oly OM 50/1.2 and quietly put it back on again after I saw what I would be dealing with inside, and called a local CLA guy up instead to fix the aperture ring sticking. :)

Can I safely access or disable the zoom lock on a Tamron 24-70mm f/2.8 Di VC/USD to free it from 24mm?

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