One of widely used lenses by both photography professionals and amateurs is Nikkor 28-70/2.8D, which is prime zoom, suitable for everyday shooting. It covers most of scenarios for generic purpose lens, and provide decent quality even by today standards.
This 935g lens is not produced anymore, being replaced by newer AF-S 24-70/2.8G in 2007, which in turn already upgraded to AF-S 24-70/2.8E VR. All these full-frame lenses are fixed wide f/2.8 aperture at all focal distance ranges, have fast auto-focus and good sharpness.
My particular 28-70/2.8 was acquired from eBay as used, and was serving me well for over two years, till very last couple months. Focusing near 3m distance become stiff and stuck about 3meter focusing distance, according to distance scale in lens barrel window. Lately it stopped turning at this point completely, producing wild squeal during rotation in attempt to push it thru. Focusing ring still was turning, but internal lens elements were not moving, which is was visible by stuck focal marks window. Condition was same either using AF mode or manually focusing, on both cameras, D3 and D800.
First fear was failure of ultrasonic SWM motor, which is rather common for this model, but then lens would be still normally functional in manual MF mode.
SWM replacement is costly procedure, with new motor price about 300$USD and also involving full disassemble and likely tedious adjustments.
But since my lens had focusing stuck even in manual, it looked like purely mechanical issue, having something stuck or bent internally.
The only way to find out – open the hood and check what could be broken.
To help this, I got Nikon’s service documentation, to be used as a guidance.
First I removed screws holding bayonet mount and top outer piece of enclosure.
Now outer zoom barrel with zoom ring can be removed. Two wires from M/A-M switch must be carefully desoldered from electronics FPC, to allow separation. This part had no problems and was left aside.
Tried to rotate focusing ring quickly revealed issue. One of FPC segments from inner side of aluminum support frame got loose, and got in the way of moving focusing barrel elements.
FPC is fixed to aluminum hexagon shaped frame by sticky tape, so I just reused double-sided tape and fixed FPC back to metal frame.
After this simple operation, I tried to turn focusing ring and it moved freely to both ends, without any resistance or issues.
After careful assembly, in reverse order, I attached lens to D800 and it worked without problems, with both autofocus and manual focus.
Hence repair was completed, and took about an hour, most of which I spent to adjust and assemble all parts back in proper manner, as they were originally. Be careful working on repairs like this, and keep workplace bench tidy. Parts, screws and damper springs in these lens are often tiny and hard to find once lost.
Complete process was recorded in short 1 minute-long 4K timelapse:
No missing screws and knobs were left after this repair!
If you have any questions, feel free to comment.
Modified: Jan. 4, 2016, 2:18 a.m.