[Nino8]

Hello all,

I hope all is well. Yesterday received a Pentax 6x7 MLU ver with 45mm, and after inspecting I noticed that I'm having an issue. The first time when I was trying the meter with dry fire I noticed that on "AUTO" the needle didn't move but on "MANUAL" it seems that it started to move. Today it doesn't move even putting on "MANUAL.

I've researched Reddit and some Pentax forums and it seems this is very common for these prisms that they have the issue with the built-in light-meter. I've also checked for the contacts and I couldn't find any issues or rust on them.

What steps have I've done:

Removed the lens

Removed the prism

Attached is the prism

Put the lens back

Turned on the light meter - the needle doesn't move Auto or Manual

................................

I've also swapped two new batteries and it is indicating red that the battery is working. My question is this light meter broken or am I doing something wrong? I don't much care if this meter works or not (it will be great for use for quick and dirty photos) because I'm mostly using my external Pentax Digital Spot meter but I want to complain to the eBay seller. Thanks



Here are some photos:

https://ibb.co/hBH7Q3D

https://ibb.co/DWMT0qT

https://ibb.co/LC8tQ5m

[tuco]

I shoot with the folding hood most of the time and my TTL prism laid idle for over a decade. One day I wanted to use it. I put it on and it didn't work. I did the usual of cleaning the contacts and verified the aperture chain wasn't broken (can happen if prism and lens are not installed in the correct order) and still nothing. But when I cycled the ISO adjustment back and forth from mininimum to maximum several times, it started working again. Maybe try that and see if you get lucky too.

Best of luck.

[vandergus]

I shoot with the folding hood most of the time and my TTL prism laid idle for over a decade. One day I wanted to use it. I put it on and it didn't work. I did the usual of cleaning the contacts and verified the aperture chain wasn't broken (can happen if prism and lens are not installed in the correct order) and still nothing. But when I cycled the ISO adjustment back and forth from mininimum to maximum several times, it started working again. Maybe try that and see if you get lucky too.

Best of luck.

This kind of makes sense with my understanding of how these metering systems work. I don't have any experience with the 67 meter but it sounds similar to the basic "center the needle" type meter in the K1000.

The way these systems work is by balancing current between two separate circuits. Both circuits run current through the galvanometer. When the current is balanced, the needle is centered. If there is an imbalance, the needle is offset. One of the circuits is the CdS cell (aka the light meter). As the amount of light hitting the sensor changes, the current through the galvanometer changes. The second circuit contains a couple variable resistors which represent different aperture and shutter speed settings. As you change the aperture and shutter speed, the current through the galvanometer changes. The ISO setting is often couple with the shutter speed setting and they both share the same resistor.

When the exposure needle is pegged either high or low, it means that one of these circuits is open. With an infinite resistance, the current in the galvanometer cannot be balanced and the needle is held to one side. In the K1000, if the needle pegs low, that means the circuit containing the shutter and aperture resistors is open, usually due to some oxidation or corrosion on the contacts. If it's just some light oxidation, actuating the knobs and dials can be enough to "clean" the contacts and get it working again. That sounds like what happened in tuco's case. If that doesn't work, a good servicing should be able to get it back in working order.

[Nino8]

I shoot with the folding hood most of the time and my TTL prism laid idle for over a decade. One day I wanted to use it. I put it on and it didn't work. I did the usual of cleaning the contacts and verified the aperture chain wasn't broken (can happen if prism and lens are not installed in the correct order) and still nothing. But when I cycled the ISO adjustment back and forth from mininimum to maximum several times, it started working again. Maybe try that and see if you get lucky too.

Best of luck.

It actually worked your advice but only on Manual mode set on the lens. I think when it is set on manual it gives you -1 exposure if I'm not mistaken. If it works on Manual but not on Auto is this a Lens issue? Thanks

---------- Post added 02-12-23 at 03:12 PM ----------

This kind of makes sense with my understanding of how these metering systems work. I don't have any experience with the 67 meter but it sounds similar to the basic "center the needle" type meter in the K1000.

The way these systems work is by balancing current between two separate circuits. Both circuits run current through the galvanometer. When the current is balanced, the needle is centered. If there is an imbalance, the needle is offset. One of the circuits is the CdS cell (aka the light meter). As the amount of light hitting the sensor changes, the current through the galvanometer changes. The second circuit contains a couple variable resistors which represent different aperture and shutter speed settings. As you change the aperture and shutter speed, the current through the galvanometer changes. The ISO setting is often couple with the shutter speed setting and they both share the same resistor.

When the exposure needle is pegged either high or low, it means that one of these circuits is open. With an infinite resistance, the current in the galvanometer cannot be balanced and the needle is held to one side. In the K1000, if the needle pegs low, that means the circuit containing the shutter and aperture resistors is open, usually due to some oxidation or corrosion on the contacts. If it's just some light oxidation, actuating the knobs and dials can be enough to "clean" the contacts and get it working again. That sounds like what happened in tuco's case. If that doesn't work, a good servicing should be able to get it back in working order.

Thanks

[tuco]

It actually worked your advice but only on Manual mode set on the lens. I think when it is set on manual it gives you -1 exposure if I'm not mistaken. If it works on Manual but not on Auto is this a Lens issue?

Is the aperture chain working ( not broken)?

EDIT: With a lens in auto mode, the aperture remains wide open and as you rotate the aperture ring on the lens to various f-stop settings, a metal tab on the camera body common to the bottom and lens side of the prism slides back and forth on a chain that adjusts the TTL metering accordingly. And if the chain is broken then the TTL never knows you changed aperture and remains unreponsive but it will responed in manual, stop-down metering mode.

[Nino8]

Is the aperture chain working ( not broken)?

EDIT: With a lens in auto mode, the aperture remains wide open and as you rotate the aperture ring on the lens to various f-stop settings, a metal tab on the camera body common to the bottom and lens side of the prism slides back and forth on a chain that adjusts the TTL metering accordingly. And if the chain is broken then the TTL never knows you changed aperture and remains unreponsive but it will responed in manual, stop-down metering mode.

Hi Tuco,

By inspecting the aperture chain looks in really good condition. Even I've tried to see the chain when putting the lens if the chain is going to move. Looks like the chain is moving as expected. I'm not sure where the problem occurs. It works most of the time in Manual but not in Auto. The problem here is that I got the camera from one seller and a lens from another seller. I need to identify where is the issue so I can ask for a partial refund from the particular seller.

Here are some photos showing that the chain is in place and the contacts look in ok condition:
https://ibb.co/vjxngf4
https://ibb.co/h7zgBWT
https://ibb.co/wMtP22d

I've also tried to record to show that the chain is actually moving but I couldn't perform the whole rotation with one hand which is why I don't show the full rotation.
330016547_6141394229239267_5558966427621281641_n

[tuco]

In your video you are putting the lens on and you can see that tab on the chain moves to the initial position. Okay. Now when you adjust the aperture ring on the lens that tab should move more. That's the interfaces with the TTL of course.

In Manual mode the TTL meter is forced to see an aperture/light level change. And since the meter works in Manual Mode (that part of the meter is working) and not in Auto Mode says to me there is a problem with either the interface between the camera body and the TTL or the internal business of the meter is not responding to the physical position changes via the tab on the aperture chain.

[Nino8]

In your video you are putting the lens on and you can see that tab on the chain moves to the initial position. Okay. Now when you adjust the aperture ring on the lens that tab should move more. That's the interfaces with the TTL of course.

In Manual mode the TTL meter is forced to see an aperture/light level change. And since the meter works in Manual Mode (that part of the meter is working) and not in Auto Mode says to me there is a problem with either the interface between the camera body and the TTL or the internal business of the meter is not responding to the physical position changes via the tab on the aperture chain.

Thanks! I will flag this to seller who sold this camera. Thank you so much for the feedback and help!