[Added February 27, 2010]: After looking at the 77 page repair manual for this lens, I don’t recommend that you attempt this repair yourself. Lens optical equipment, a wave output analyzer and other specialized tools are used in the repair of this lens. If you attempt this repair yourself, you will likely never get the lens working like new.
I somehow managed to get lucky and was able diagnose the problem with my lens and repair it, with the auto-focusing, manual focusing, manual zoom and auto exposure all working again. You may not be so lucky, read the comments. I am not sure how my repaired lens would compare in resolution and sharpness with a new lens.
[Added April 30, 2009]: If you don’t feel confident doing this repair yourself, I recommend you send your lens to a Nikon Repair facility. Remember, if you are unable to repair it yourself, you will have a paperweight, a lens that might not autofocus or at least a more costly repair if you send it to Nikon.
[Original post]: Our Nikon D70 came with a “kit” lens, the relatively highly regarded AF-S DX Zoom-NIKKOR 18-70mm f/3.5-4.5G IF-ED.
After a couple of years of non-professional use, the zoom ring suddenly became balky. Sometimes it would get stuck between 24-50mm, occasionally, it would zoom all the way to 70mm. It felt like there was something jamming the zoom mechanism, so I tried blowing Dust-Off in from the front and rear, hoping that would dislodge the offending chaff. That didn’t work.
It didn’t make much sense to me to send in for repair a mostly plastic lens that costs $350 USD new or used on eBay for $175 USD. Besides, I probably wouldn’t buy another 18-70mm lens. The Nikon AF-S DX VR Zoom-NIKKOR 18-200mm f/3.5-5.6G IF-ED or the Nikon AF-S DX Zoom-NIKKOR 12-24mm f/4G IF-ED would be my first choices.
I started at the rear of the lens and removed the screws holding the bayonet mount to the lens. The fact that there are a row of electrical contacts made me think that it was likely that the patient wouldn’t survive the surgery.
Under the bayonet ring there was a circular printed circuit board with various flex connectors encircling it. I pried all of the connectors free and unscrewed the rear element.
I eventually stripped the lens to the point where I could see the zoom mechanism and how one of the three screws mounted every 120 degrees around the body of the lens was loose. The nylon foot that it screwed into was now rattling around inside the lens. When it dropped out, I inserted it back into it’s groove and used nail polish on the screw threads to hopefully keep it from vibrating loose again. The lens was assembled with some sort of thread locker on the screw but it still managed to vibrate loose.
As they say in the auto shop manuals, reassembly is the reverse of disassembly. The first time I put it back together, the zoom worked fine, but the camera didn’t auto-focus. After taking the lens apart again, I saw that the focusing prong was connected to the drive mechanism. Another hour later, it was working.
Remember, don’t try this at home.