David Mann wrote: > Pentax 6x7 TTL prism for �50, I think its broken as I can't see the > needle....
and William Robb replied: > Yes. When the prism is removed, the meter needle should be visible, > pointing at the minus indication. Hi Dave, I may have some good news for you. I bought a TTL prism finder with an ~allegedly~ inoperative meter. Mine had the same symptom as yours -- that is, I couldn't see the needle in the viewfinder. Turned out my metering circuit actually ~did~ work, and the reason I couldn't see the needle was because a reflecting optic inside the housing had come unglued. It was ~very~ simple to fix. I suspect this might be a common problem. This reflecting optic is actually a little rectangular prism that sits just in front of, and just slightly below, the eyepiece. You'll need to remove the cover from your TTL prism finder to get access to this piece. Removing the cover is fairly simple. Once the cover is off, the rest is pretty straightforward. Here's how.... (1) Remove the shutter speed dial assembly. You may want to first set the ASA at something like 100, and the shutter speed position to something like 1/60. To remove this dial, you'll need to loosen and remove the screw in the center of the dial (you can bend a paperclip to fit into the holes on this screw, then twist anticlockwise, using a pair of tweezers to securely grasp both sections of the paperclip). Lift off the dial, then the ASA indicator wheel and spring underneath. (2) Remove the "Asahi Pentax" (or "Honeywell Pentax") plastic nameplate from the front of the prism finder cover. This nameplate is held in place with a little glue. You'll see a couple of screw heads once you remove the cover. (3) Finally, remove the seven or eight screws holding the prism finder cover in place. There are two in the front, two in the rear, two on one side, and one or two on the other side. (4) Now it's time to find out if the metering circuit works or not. With the cover off, you can now see two important things -- one of these important things is the meter itself, along with the "+" and "-" exposure indicators. It will be over toward the left as viewed from the rear of the prism finder. Take your 6x7 body, and remove the lens if one is attached. Mount the meter onto your 6x7 body, making sure the detents click into place. Mount a lens on the body, making sure the lens is set to the "AUTO" position. You now want to turn the TTL finder circuit "ON". You'll have to manually switch the TTL finder circuit on by momentarily touching the two "ON" connectors together. Now point the lens to a bright light, and watch the meter needle for a response. If the needle responds as it should to more or less light, increased or decreased aperture (set at the lens), and increased or decreased shutter speed (set by moving the little potentiometer under the shutter speed/ASA dial), then your metering circuit is just fine. (5) Now to fix the reflecting optics. It may be best to remove the prism finder from the body at this point. I mentioned in Step #4 that there are two important things you can see with the prism finder cover removed -- one of these things is the meter itself, and the other thing is a pair of screws holding the eyepiece housing to the rear of the prism finder body. You'll need to remove this eyepiece housing to see the little rectangular reflecting optic I mentioned at the beginning of my note. Remove the two securing screws, then CAREFULLY tip the eyepiece housing away from the prism finder housing. (I say "carefully", because there are a couple of delicate wires inside this eyepiece housing which connect the power contacts to the metering circuit board. They're prone to break at the contacts, and they ~can~ be resoldered, but it's kind of a nuisance to have to do that, so be a bit careful.) (6) With the eyepiece housing tipped away from the prism finder body, you should see a little blackened rectangular glass prism located just in front of and below where the eyepiece was located. IIRC, prism dimensions are about 5mm x 5mm x 20mm. Chances are this little rectangular prism has come unglued. You can probably push this little prism back and forth in its milled recess with your fingers, or a stiff piece of card, or a dental pick, etc. Slide it so the angled, unblackened end is roughly centered under the eyepiece area, then temporarily hold the eyepiece housing back in place and see if the meter is now visible in the bottom center of the prism finder field of view. (It helps to allow light from a desk lamp to illuminate the top area of the finder, above the meter.) You may have to repeat this a few times, but you should eventually find a position for this little reflecting prism where the view in the eyepiece looks the best. Without allowing the little reflecting prism to move, inspect its optimal position, then glue in place with a little contact cement or Super Glue. Now reattach the eyepiece housing and tighten the two screws securing it in place. (7) Just to the left of the eyepiece housing, you'll see two tiny square mirrors mounted on somewhat flexible metal mounts. It's fairly simple to ~very slightly~ move one of these mirrors by using the access hole on the back of the prism finder, just to the left of the eyepiece. You can push on its mount with a stiff needle, dental pick, etc. IIRC, a slight back-and-forth (left-to-right) deflection of the metal holding this mirror causes the view of the meter in the eyepiece to rotate a bit. You can try this if you like, but if you're satisfied with the view from Step 6, I'd leave well enough alone and not try to adjust this mirror position. (8) Now it's time to reassemble the prism finder. Slide the finder cover in place and secure the screws around the outside of the cover. Glue the "Asahi Pentax" nameplate in place with a little contact cement. Finally, reassemble the spring, ASA indicator wheel, and shutter speed dial, securing this assembly with the little screw with the two holes in the top. Hope this helps, Dave. I've also got an equally detailed procedure for repairing your own aperture coupling chain, in case you ever have to do this. Maybe we should cull all these repair tips together and post them on a web site somewhere? Does anyone have some server space, and have any other folks on the list documented their own experiences with some of these repairs? Cheers, Bill Peifer Rochester, NY - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
