A pack of Pentax gear recently emerged on a local classified site and it contained, among other nice items, a Pentax DFA 150-450mm lens. At the list price provided I did not hesitate (in fact I was tempted to fly to the city where it was located and buy in person).
Anyway, with every good buy comes risk and so it happened for me. The Pentax DFA 150-450 had the dreaded zoom jam and zoom lock switch freeze. Bummer right?
Well, since the lens was out of warranty and I really had no recourse against the seller (purchase price was ridiculously low), I decided to have a go myself.
And it wasn't a silly decision at all!!!!!!
In the image below I show with the red arrow a set of sandwiched 'spacers' located just inside the rear mount. You can get to this part of the lens by removing three screws and the rear element shroud (real easy after some gentle force to remove the shroud).
The picture shows the spacers in the position they ought to be in. The 'blockage' (not shown as I fixed it before taking a photo), was simply rectified by pushing one of the misaligned spacers back into place. Imagine one of the spacers being dislodged and 'poking out' - blocking the retraction of the zoom all the way back to 150mm setting.
Magically, after restoring the removed shroud I tested the zoom lock feature. Wha la! FIXED.
So, if you are inflicted by this problem (or are worried by it), do not fear. It is a truly easy fix. You do not need courage (despite the lens being really expensive. Just a JIS screwdriver, some good lighting, a little patience and you will have the problem fixed in 20 minutes flat.
As for dust in the elements problem - EASY fix there too. Remove the front element grouping by screwdriver and one inner element with a lens wrench and then you can blow away all the dust!! Easy.
As for the price I paid for this lens I am not sharing (and I do not feel guilty either!) - the seller decided the cost of repair was too great and in wanting to get some money back was not entirely truthful in their declaration on condition. One of the rare times you end up being rewarded I guess.