Help! SMC Pentax-A 50mm should work on K-m / K-2000?

I urgently need some help.

I have a brand-new Pentax K-2000, bought a month or two ago. Today I received a lens I bought from an ebay seller - its an SMC Pentax-A 50mm f1.7 prime lens I bought to replace a similar 50mm SMC Pentax-M f1.7. Basically I wanted to use the automatic aperture so I wouldn't be guessing the metering etc.

I can't get the lens (which is set to 'A') to function at all on my camera unless I enable the 'allow aperture ring' setting in the settings, which presumably I shouldn't have to?

I've been looking around the web and in my camera's manual and it seems that this lens should work in eg. shutter priority, aperture priority etc and should display the F-stop number.

The aperture ring itself seems stiff and 'sticky' or juddery. Worse, the ebay seller is being weird about it - he is offering to take it back, but he told me i know (and i quote) "F*CK ALL!!!". Bizarre.

So... am I correct in thinking this lens should work? Help!

if the lens is on 'a' setting and your setting the aperture on the body or in one of the automattic modes it should work.
the aperture ring, off the 'a' modes should turn easily and click into the f stops nicely. if it feels weird turning, send it back. if turns properly, try cleaning the contacts... (quick rub with a pencil earaser, and swab it with a q-tip moistened with wd-40 or alcohol...

Yes you do have to.
Allow aperture ring should be set to on for most (if not all) older lenses .. to be honest I really dont know why Pentax even have the option to turn it off.

No you don't. If the lens has an "A" on the aperture ring and you set it to "A" then nothing further needs to be done. The camera will give you full function, although obviously a manual focus lens will still be manual focus.

Thanks all. Don and John Riley are correct (sorry Mike-P) - it should indeed work with factory settings with the aperture ring set to 'A'.

I have in fact just proved this to myself by attaching an SMC Pentax-A 28mm f2.8 to the camera. It works correctly.

I noticed something else - with the 28mm, the camera asks me for the focal length whenever I power it on. This is for the SR to work properly. However, with the 50mm lens attached it has only asked me once or twice and now I cant get it to ask me at all.

Also, as Don points out, the aperture ring should turn cleanly. The ring on the 28mm does, while the 50mm is a struggle to turn, and it sticks and judders. Methinks this lens is in need of repair.

Many thanks for the input gents - going to send this one back and get a refund.

Having read this description of a common failure of the 50mm SMC Pentax-A, i'm convinced thats whats wrong with this one:

http://homepage.mac.com/jpelling/page11/page11.html

Ooops my bad ... read it too fast