[joeoptics]

Purchased a Pentax K-x with 18-55 and 55-300mm lenses when the camera was released. I love it and use it frequently. Recently the 55-300mm lens has developed an intermittent electrical failure problem. When it fails, it will not autofocus and it ignores the shutter button. The 18-55mm works fine. I notice that the gold coated contact on the 55-300 lens is partially worn away and I can see the underlying silver metal. The other lens still has the contact covered with gold. Is there a trick to repairing the contact? Is there a service that fixes these?

[MysteryOnion]

Sounds like you'll need to electro plate it or contact Pentax part for a new contact. I figure the lens is way out of warranty?
The bare metal is often a nickel coat that can oxidize easy, you could try a contact cleaner and coat it with a fine oil after... just a dab, don't hose it.
One old trick is to cover the contact with petroleum jelly to slow the oxidizing. This is just a temporary fix.

[elliott]

Is it a plastic or metal mount?

The plastic mount is part number 48167.0M107 and it is very cheap, someone on the forum bought one last year for $6.72, even if the price has doubled it is dirt cheap.

I believe the metal mount is 48000.M10801, no idea what the pricing on that one is.

[joeoptics]

Yes, the lens is way out warranty. I assume a q-tip with some isopropyl on the contact is worth a try. Would not petroleum jelly act as an insulator?

The camera side of the mount is metal for sure. The lens side I suspect is anodized metal. I see 5 jeweler screw heads on the lens side. I can not tell if the worn contact is an integral part of the piece held in by the screws. Time to Google. Thanks for suggestions.

[pacerr]

Coupl'a questions here and a point.

Gold doesn't corrode -- not to the extent of causing electrical contact problems. But it may become covered with a contaminant that affects its conductivity. Clean 'em.

It's not clear whether you're talking about the round data pins or a flat metal tab that serves as a ground contact on the plastic DA L mount. Note that the pins are spring-loaded to allow rotating the lens with minimal effect on wear while providing positive contact. Make sure none of the pins has gotten gummed up so it fails to extend completely.

Also ensure there's no rotational play in the lens lock up that could cause a miss-alignment of the data pins and the contact points on the body. Miss-alignment could also cause the mechanical focusing pins to fail to engage. Observe the spring-loaded action of the focus drive pin with the lens removed.

Note that in some modes the shutter will not release until focus is achieved if AF is selected.

H2

[JimJohnson]

This is a field fix, not meant in any way as a permanent repair....
cut a thin strip of aluminum foil, long enough to cover the contact on the camera body and dangle past the mount, but not so wide as to cover more than the intended contact. Fold the strip over the exterior of the mount so you can clamp it in place with one finger while depressing the lens release with another finger on the same hand. Press the lens into the mount and turn just enough for the bayonet to catch. Pull the lens lightly away from the mount while turning it all the way (minimize drag on the foil strip). Let go of the lens release and turn the lens backward enough to make sure it is indeed locked.

Also, isopropyl alcohol is not a good oxidation remover. Use an electronics contact cleaner instead - or, try rubbing lightly with a clean pencil eraser. Keep in mind the electronics cleaner works by desolving the oxidation, whereas the pencil erase grinds the oxidation (and potentially a bit of the contact) away.

[elliott]

The camera side of the mount is metal for sure. The lens side I suspect is anodized metal. I see 5 jeweler screw heads on the lens side.

If the mount on the lens is black, it is the plastic mount.

[joeoptics]

I want to thank everyone for the helpful comments. The problem is intermittent and as I write, I can focus. I swap lenses frequently and it is annoying to not be able to focus or take a picture reliably. The suggestion that this might be a mechanical rotational play seems like a possiblity. Is there an adjustment I can make to minimize it?


pacerr,
I refer to the flat metal tab, which appears to be gold or a gold alloy coated on a shiny metal. The gold looks partially worn off the rounded end of the flat tap on the lens which is intermittent (55-300) and is not worn off the other lens (18-55) which is reliable.