Nikon F4: Mission Aperture Lever - two ways to fix the aperture problem

Andreas Thaler · Mar 24, 2024

Andreas Thaler said:
Finally a success

One last update on my F4S, which I treated with the syringe:

The aperture lever has improved and now folds down to 50%:

View attachment 366095

That is sufficient to close the small apertures completely and happens quickly enough.

The camera can be used.

A success, even if it took several attempts

The aperture lever has been further improved and now folds down 4/5 of its way.

Very pleasing

Andreas Thaler · Mar 25, 2024

Finally I found a video that deals with the aperture problem (Japanese).

Google Translate, Japanese > English:

I removed the front panel up to the back of the preview lever, but I've already done that along with a lot of soldering. I'll explain that later when I assemble it, but I oiled the gears, and oh! The squealing disappeared!! But it was only for a moment, as I ended up removing an extra screw and wasting an hour. I'll assemble the front panel next week. Even if the squealing stops after oiling, I have a feeling it will come back after a while...

Andreas Thaler · Mar 25, 2024

Everything is now ready to treat another Nikon F4 with the aperture problem.

The candidate squawks when the stop down lever is pressed and the aperture lever in the mirror box moves only slightly.

I will remove the mirror box, analyse the problem on site, clean, lubricate, and then reassemble the camera.

So take the recommended route. This is not a shortcut, but a repair.

We start tomorrow (CET).

Stay tuned!

Andreas Thaler · Mar 26, 2024

Shortcut works

The aperture lever of the Nikon F4, which I treated with the shortcut, now moves quickly over its full length. This means that the oil has spread further and that the benzine has removed any resinous build-up.

The camera works perfectly, and there are no signs of any impairment caused by oil.

I therefore consider the shortcut with syringe, adapted cannula, benzine and Nyoil to have been a success.

The method can obviously be used to permanently solve the aperture problem.

Nevertheless, I will continue to monitor the F4, as it is my work camera and is in regular use.

Andreas Thaler · Mar 26, 2024

On the Nikon F4, the aperture lever in the mirror box can be sluggish. It then does not move the full distance or only moves slowly. Incorrect exposures can be the result.

The cause is believed to be resinification or a lack of grease in the aperture mechanism on the side of the mirror box.

As a shortcut

to not having to open the camera (which is always a risk), I successfully solved the problem by applying benzine and Nyoil from the outside, see

Nikon F4: Mission Aperture Lever - two ways to fix the aperture problem

{Moderator note 12 Jan 25: five threads on the F4/F4S aperture lever repair have been merged into the present thread. You may encounter one or two dead links to 'other' threads. The posts they pointed to, are now all part of this thread, which mostly still follows the journey in a logical and...

www.photrio.com

This method requires a few attempts, and benzine and oil must be added without being able to see the mechanism.

The shortcut carries the risk that oil will get into places where it shouldn't. It is possible that the camera will not function properly because the oil will migrate.

Classic repair

In this project, the problem is to be solved as a classic repair.

To do this, I will remove the mirror box, examine the aperture mechanism, clean, lubricate and reassemble the camera.

Disassembly is a complex process with 22 steps.

To gain experience, I have already disassembled a defective F4 for practice (see link above).

Instructions available

I am again following the tutorial from @F4user, supplemented by information in the Nikon F4 Repair Manual and an issue of the SPT Journal, dedicated to the Nikon F4 only:

Nikon F4 aperture lever repair

WARNING : Those instructions are for skilled persons with some knowledge of mechanics and electronics. Don't follow if you are unsure about your skills. F4 Aperture lever problem driving the lens down. This will be a long thread with ~100...

www.photrio.com

Nikon F4 Repair Manual

Nikon F4 factory repair manual

learncamerarepair.com

SPT Journal: January-February 1993

Society of Photo-Technologists Journal

learncamerarepair.com

Based on the experience already gained I will deviate from @F4user's instructions for cleaning and lubrication, more on that later.

I am not creating a tutorial here

but rather showing highlights of the project and going into detail about the problem with the aperture mechanism and the assembly of the F4, which is not covered in the @F4user tutorial.

Today's goal (March 26, 10:30 CET currently in Vienna) is to remove the mirror box and document the individual steps so that I have a template for the assembly.

I will continue to add to this thread.

I hope the venture is successful.

Questions and comments are always welcome

The candidate, a Nikon F4 on the battery compartment MB-23, which turns the F4 into a Nikon F4E:

The external condition of the camera is good, all functions work properly.

The aperture lever in the mirror box when the shutter is released only goes down a short distance and does this rather slowly:

Red arrow: actual position of the aperture lever
Green arrow: target position

As a result, apertures on the lens no longer close correctly above f = 8. Pressing the aperture button produces the typical screeching noise.

Andreas Thaler · Mar 26, 2024

Since I will be removing more parts than I can fit on the table, I will put them in plastic boxes that I will number with a non-permanent marker.

Since I usually put removed parts in the order they belong together, I have to document everything precisely with the camera so that the assembly is successful later.

I work on my large grounded work mat, since the electronics of the F4 will be exposed and at risk from electrostatic discharges.

Andreas Thaler · Mar 26, 2024

The left top cover is removed:

I use adhesive tape to attach components and screws that belong together.

This way, there won't be any confusion when I put them in the plastic box:

Step #1 achieved …

… and fully documented:

Andreas Thaler · Mar 26, 2024

Disassembly is progressing:

The next step is to desolder theese two cables on the base plate:

Andreas Thaler · Mar 26, 2024

March 26, 16:00 CET, Vienna

The eagle has landed

Above is the rear part of the F4 with the shutter, below is the front part with the mirror box:

Andreas Thaler · Mar 26, 2024

Along the way there were complications with three glued screws that I couldn't remove. I had to mill out the screw heads with the tungsten carbide cutter on the Dremel. Thankfully I have orginal replacements for all three.

Andreas Thaler · Mar 26, 2024

I hope that my grounding worked and that there is no damage to the electronics due to electrostatic discharge.

I also pressed twice accidentally on a flexible conductor while working and damaged a soldering point when milling out a screw.

But no serious damage should have been done. I checked the spots with a magnifying glass.

The day's goal has been achieved.

Now I'll take a closer look at the problem area:

Andreas Thaler · Mar 26, 2024

The red arrow points to the lever that tensions the mirror, the green arrow to the lever that releases the mirror.

The aperture mechanism underneath is activated by the mirror.

The screeching noise when you press the stop down lever is caused by this ratchet gear:

The ratchet gear is coupled to a perforated disk behind it (red arrow). This disk runs through a photointerrupter underneath (blue arrow) generating electronic pulses that are sent as signals to the control electronics of the F4:

What is a Photointerrupter? | Electronics Basics | ROHM

Photointerrupter information

www.rohm.com

The ratchet gear should run quickly and freely when the mirror folds up.

Here it runs sluggishly, as do the gears it is connected to.

I will clean the mechanism with benzine and then oil the axes of the ratchet gear and the gears sparingly and move the mechanism through.

Andreas Thaler · Mar 26, 2024

After several times putting benzine into the mechanism, moving it around and drying it with the bellows, the gears run more easily, but still not completely freely.

The screeching noise when pressing the stop down lever, which was no longer audible during the benzine bath, is also back.

After I put a drop of Nyoil on the axle of the ratchet gear, the screeching suddenly disappeared. So there was a lack of lubrication here.

The axles of the other gears also get oil.

Now the mechanism runs easily and freely

Andreas Thaler · Mar 26, 2024

I will continue to move the mechanism and observe it. If everything stays as good as it is, hereby the repair is done.

Tomorrow the long journey back begins, the assembly. I hope it works.

Stay tuned

Andreas Thaler · Mar 26, 2024

Here is a slow motion shot with the iPhone.

The ratchet gear rotates now quickly after the mirror is released. Too fast for the eye:

Andreas Thaler · Mar 26, 2024

The current status:

Andreas Thaler · Mar 26, 2024

Stubborn screws

Milling out the screw head is the last resort if a screw cannot be removed. This means that the screw is lost in any case and damage all around it is almost impossible to avoid.

Here I previously tried to free the screws, which were presumably secured with adhesive, using heat (soldering iron tip), but that didn't work.

I deliberately did not want to use acetone as a solvent for the adhesive here, as flexible circuit boards are arranged around the three screws.

The two adjacent screws were milled out with the tungsten carbide cutter on the Dremel without causing any significant damage to the tripod plate above.

With the PZ-57 (Nejisaurus) pliers I removed the stuck remainders of both screws:

With the screw in front of the shutter speed knob, I slipped with the Dremel and damaged a soldering point:

@koraks My Dremel drill stand would not have helped here, as the milling cutter hits the screw head vertically, which causes bouncing.

I had to set it up horizontally and then slowly guide it inwards.

I have original replacements for all parts.

The soldering point should not be affected by the damage. Anyway I won't know until after assembly.

Andreas Thaler · Mar 27, 2024

March 27, 9:00 CET, Vienna

The cleaned and oiled aperture mechanism has not changed overnight and works perfectly. All parts run smoothly and freely, without any annoying noises:

So today's goal is to assemble the F4 and then test its functionality.

It will be exciting

Andreas Thaler · Mar 27, 2024

Assembly: Connecting the front and back parts

@F4user does not go into the assembly in his tutorial so I am showing preparations to connect front and back part.

Details can be found in the Nikon F4 Repair Manual (pages A 45 - 47, also in various places in the SPT Journal, see links in this thread).

When connecting the front and back parts, some parts must be put in position beforehand so that the coupling of the mirror and shutter mechanism works:

The mirror is tensioned via the charging lever.

The slider for the filter above the photocell is moved to the left.

The coupling for the filter lever on the mirror box is pushed towards the film cartridge chamber in the back so that both parts can connect.

The correct levers position for T on the shutter speed dial.

The shutter speed dial must be set to T. This is one notch away from X, which has a lock. The lock button is pressed in and the dial is turned clockwise, looking from the shutter to the mirror box.

Position of the clutch levers for cocking and releasing the mirror. Nothing needs to be adjusted here.

Finally the mirror box on the front part is inserted into the rear part.

Andreas Thaler · Mar 27, 2024

The front and back parts are connected again.

You should pay attention to the unit with the LEDs and LCD on the mirror box, it hangs freely on a flexible circuit board.

With a little gentle movement back and forth, the front part snaps into place:

To check whether the couplings for the filter are engaging, this slider can be moved back and forth. If it clicks into place in two positions, it fits:

Andreas Thaler · Mar 27, 2024

That was the critical step with the connection of the front and back parts.

I won't know if everything works until the F4 is mounted.

To do this, I'll follow the tutorial from @F4user again, this time from end to beginning.

Andreas Thaler · Mar 27, 2024

March 27, 14:45 CET, Vienna

Back to Earth

The assembly worked, apart from the covers the F4E is complete again.

All tests passed without a hitch.

And the aperture lever now folds all the way down and as quickly as it should

What a day!

Andreas Thaler · Mar 27, 2024

Conclusion

Repairing the problem with the aperture lever is a lot of work, but it is doable with repair skills.
Apart from three stuck screws, I didn't encounter any problems.
@F4user's tutorial is an excellent guide to disassembly.
For assembly, I recommend the relevant pages in the Nikon F4 Repair Manual (see thread). I hope that my explanations are also helpful.
Some connections have to been (un)soldered, which was no problem. All soldering points were easily accessible.
To keep an overview, a filing system for the removed parts is recommended. Pictures for orientation are useful as always.

Now the question is what is better: the shortcut without having to disassemble the camera or repair it.

I'll start a separate thread about that.

+++

All information provided without guarantee and use at your own risk.

Andreas Thaler · Mar 27, 2024

Addendum

I deliberately did not remove parts of the aperture mechanism around the ratchet gear so that I could clean them. @F4user shows this in his tutorial.

The reason for this is that doing the removing a spring there looses its tension and I do not know the correct tension.

I also did not examine another spring, which @F4user sees as further cause of the aperture problem (fatigue).

I could not have done anything here, as I have neither a reliable replacement nor any knowledge of how to re-tension the spring.

But the repair worked anyway.

Andreas Thaler · Mar 27, 2024

The F4 does not need to be adjusted after the front part with the mirror box has been reattached, at least I found no information about this in the Repair Manual and SPT Journal.

However, if the front part with the mirror box is replaced, the AF adjustment, which is stored in an EEPROM, is lost.

The AF of the F4 would then have to be readjusted, which requires a special Nikon device that is most likely no longer available.

Nikon F4: Mission Aperture Lever - two ways to fix the aperture problem

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