K1000 Battery - How does it work?

Trying to repair my Pentax K1000. The meter seems to work, the only problem is that the battery isn't making good contact, so it's inconsistent. The negative terminal inside the camera is a pronged piece and then behind/beside it I see two recessed round contacts. Are these the positive contacts? How is the connection made between the positive of the battery and the camera? Does the cap serve some purpose to make contact with the sides of the battery and these contacts?

All the contacts are clean, by the way, the battery is new, and the wire connecting the battery assembly to the meter is also good.

Thanks.

Not the best picture, but you can see the negative terminal and two round contacts.


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The 'case' of the battery is the positive terminal and it goes face up in the opening. The camera cap completes the positive contact.

Is the flat prong pushed down so that it is sitting too low and therefore not making a solid contact with the battery? Is the prong free to move at one end? If that's the case, then just gently bend it upwards.

The two small circles in the base are rivets holding the central contact in place.

There is a meter switch in the camera. At the back of the prism, just above the eyepiece is a cell that conducts
when the lens cap is removed. Are the solder joints or the cell itself good?

Thanks everyone. The prong is pushed down, and I was tipped off by PM that the small circles are in fact rivets. Thing is, I can move the battery around in its compartment and see the meter switch on and off. At one point, it would respond just fine until you started tightening the cap.

If it is all working you put the battery in and screw on the baseplate cap with 'dime'.

Think some caps are threaded some two bayonet lugs... Dependent on decade manufactured.

It works but then starts to fail as the cap is tightened... is the battery of the correct dimensions?

Yes. I've used an LR44 and a 357. Same experience with both.

The dry cell in the K-1000 goes into the chamber with the POSITIVE end facing upward towards the user (facing the bottom of the upside-down camera). See page 7 in the manual.

http://www.cameramanuals.org/pentax_pdf/pentax_k1000-1.pdf

With respect to

I can move the battery around in its compartment and see the meter switch on and off. At one point, it would respond just fine until you started tightening the cap.

Click to expand...

Here’s what I think MIGHT be happening:

The formed flat electrical contact in the bottom of the chamber contacts the negative terminal of the cell. If the flat contact is misshapen, as the cover is fully screwed down it might be possible for the flat contact to bridge across to contact both the center negative terminal of the cell and slightly touch the outer part of the cell case which has continuity with the POSITIVE terminal.

That would create a short circuit and prevent current from reaching the meter circuit. If left this way long enough it would soon deplete the cell. This isn't necessarily the problem but should be checked.

Possibly you could test this by making a thin insulator of some sort to prevent the flat contact from touching the POSITIVE casing on the cell.

A small piece of tape positioned with tweezers onto the appropriate area of the flat contact, or simply covering the end of the cell near the +/- separating insulator of the cell case might serve to answer the question: Is the bottom contact bridging across the +/- gap to short-circuit the cell?

This might not be the cause of your problem, but is something to investigate.

Sometimes, the wire leading to the center contact becomes corroded. That may be what's happening to yours. As the corrosion (you can't see it, it's inside the camera).

It is possible to check and possibly repair the issue yourself, depending on how mechanically apt you are. All you need is a 2.0mm JIS screwdriver to find out. (you might get away with a small 'phillips' jewelers screwdriver, but you run the risk of damaging screws)

Start by removing the battery, and lay it and the battery holder/cover aside.

Remove the three screws that hold the bottom plate on the camera. Important note: Although all 3 are the same thread size & pitch, the middle one has a slightly smaller head. So you'll need to keep track of that one. Once the 3 screws are safely stowed away, separate the bottom cover of the camera by pulling it straight away from the body.

The place where the button battery sits is a small, molded plastic piece held on by another 3 screws. Remove those screws. There might be a small wire in the way of one, so you'll need be carefully move it out of the way. Then, the plastic battery part should simply lift away from the camera. But don't pull too hard.... there's a wire attached to the other side.

Or..... is there? If the connection got corroded, the wire has become disconnected from the battery terminal attached to the plastic piece. If you have access to a small soldering rig, you can simply resolder the connection and reassemble everything.

Presto! A working K1000 meter!

I've rejuvenated 5 or 6 K1000s 'dead meters' this way over the years.

Thanks. I've gone through that process already and repaired the wire (it had corroded and fully separated). The issue appears to be entirely with the battery.

By PM I got a suggestion to use a pencil eraser to clean the contacts and surrounding conducting metal. Could that remove something that vinegar couldn't? It didn't seem to hurt, and that along with a new cap (one from a non-working ME Super) seems to have fixed the problem. The real test will be if it still works in a week or two...

Is the battery cover original to the camera? I think there's 2 or 3 different battery versions of the K1000.