AF-S 300/4 lens won't auto-focus?!

[tom_lusk]

<p>I dug out my 300/4 after not using it for approx. 2 years, as a friend wanted to buy it.<br>

When I put it away, it was working fine.<br>

When I took it out, attached it to my D750, it would not auto-focus at all. I tried it on my old D300 and it eventually did auto focus, although it made some whining sounds for the first 10-15 seconds. Then it worked perfectly, focusing quickly, for approx. another 30 seconds. Then it quit. Manual focusing is fine, but not for the potential purchaser.<br>

I cleaned the contacts, and tried it on the D750, D300 and D2x - nothing.<br>

The lens is long out of warranty. Is there anything I can try before sending it in? <br>

All help/suggestions much appreciated.</p>

[alan_olander1664878205]

<p>The AF motor is probably bad. Mine did this, and it appears to be a somewhat common occurrence. About a $300-$400 fix.</p>

[ShunCheung]

<p>Unfortunately, it sure sounds like the AF motor is dead. Somehow the D750 has more problems with the 300mm/f4 AF-S (old version without VR and PF). Mine works ok without any TC involved but the D750 cannot drive it with a TC-14E in the middle. However, when AF also fails with the D300 and D2X, the problem is different. A couple of months ago, <a href="/photodb/user?user_id=5235717">Avishek Aiyar</a> had the AF motor replaced on his 500mm/f4 AF-S by Nikon in Long Island, New York. The cost was in the $400+ range: http://www.photo.net/nikon-camera-forum/00dUGc</p>

<p>I would imagine that repair cost for Nikon Canada in the Toronto area is similar and hopefully it is a bit cheaper for the smaller 300mm/f4 AF-S.</p>

[Dieter Schaefer]

<blockquote>

<p>Mine works ok without any TC involved but the D750 cannot drive it with a TC-14E in the middle.</p>

</blockquote>

<p>That's a sure sign that your lens needs to be re-chipped. There was an issue with early lenses where the TC added too much resistance into the path. Apparently, there is even a technical memo somewhere on Nikon's website that describes the fix. The issue has come up on flickr <a href="https://www.flickr.com/groups/2682619@N24/discuss/72157647884559639/">https://www.flickr.com/groups/2682619@N24/discuss/72157647884559639/</a> and at least one person has gotten her lens fixed (albeit not by Nikon since hers was a gray import).</p>

[alan_wilder1]

<p>I had a similar problem with my out of warranty 300/4 AF-S not autofocusing on my D750 but my focused perfectly on other bodies like my D800, D700, etc. Nikon initially CLA and replaced the SWM on service which did <strong>not</strong> fix the problem. After 3 unsuccessful attempts (even keeping my body for good measure), they eventually replaced a component called the DC/DC converter (at my insistence) which did the trick. Although it sounds like your SWM needs replacing, I would <strong>insist</strong> they <strong>also</strong> replace the DC/DC converter. If they only CLA, replace the SWM motor and it still doesn't autofocus, the DC/DC converter is the likely culprit.</p>

[doug_orama]

<p>I had the same problem a couple of years ago. Sent it to Nikon Pro, got it back with a brand new AF motor. Seemed OK. It's a backup so it ended up in the closet for several months. Took it out to do some shooting one day and it would barely move intermittently. After a while it completely quit.<br>

So I don't know if Nikon lied to me about the new AF motor and stole $350 from me, or there's some other problem that causes this. It's frustrating to pay somebody a lot of money for nothing in return.</p>