Nikon F4: Servicing and fixing the aperture control; adjusting/replacing the shutter

[Andreas Thaler]

In this project, we will examine how to disassemble the Nikon F4 for aperture control service. For background information, see here.

A common issue with the F4 is that the aperture control lacks oil, which prevents the smaller apertures in particular from forming correctly.

Master Larry Lyells, the undisputed authority on repairing electromechanical SLR, provides a solution in his article in the SPT Journal, which is entirely dedicated to the Nikon F4. However, it appears under “Tips for troubleshooting without disassembly”:

2. For erratic exposures, pull down
the aperture lever from the front of the
mirror box, Fig. 10. If you feel rough
movement or hear a noise, lubricate
the pivot of the ratchet gear, Fig. 14,
with shutter oil.

p. 24 ibid.

Unfortunately, Larry doesn't explain how to access this area from the outside. So we have to take the long way around and remove the front panel along with the mirror box to gain access.

We tested and discussed a workaround here that involves injecting oil into the camera from the outside using a syringe. However, this method is imprecise because the area cannot be seen, so the oil is injected in an uncontrolled manner. This can lead to new problems that make it necessary to disassemble the F4 in order to fix them.

I’ll walk you through the process again here, since the post I mentioned is a long workshop report and therefore a bit hard to follow.

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To check whether your Nikon F4 is affected by this issue, click here.

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The shutter in my F4 no longer forms the short exposure times correctly. So we will also remove the shutter to adjust respectively replace it.

This work is not necessary for servicing the aperture control.

All the steps and work mentioned here are described in detail in the SPT Journal January/February 1993. The SPT Journal guides you through the process. It also provides instructions for reassembly.

The SPT Journal is the only professional reference for this type of work apart from the Nikon F4 repair manual.

The work, including soldering, is not complicated but extensive. As always, it is advisable to document each step with photographs and to store the removed parts in an orderly manner.

Since the F4 contains electrostatic-sensitive components, it is advisable to work in accordance with ESD guidelines.

I will limit myself to briefly listing the individual steps with pictures and notes.


The following work steps are described in the SPT Journal:

1. Sequence to remove release-side top cover
2. Sequence to remove rewind-side top cover
3. Sequence to remove bottom cover
4. Sequence to remove front-plate/mirror-box assembly
5. Sequence to remove shutter block

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1. Sequence to remove release-side top cover

The speed dial rubber grip may already be dry and brittle. In this case, I recommend not pulling or prying off the ring, but cutting it with a sharp knife. The cut edges can be neatly glued back on when reattaching.

The cap at the top of the compensation dial is made of plastic and glued on. I carefully pry it off with the blade of a small flathead screwdriver. I don't want to use isopropyl alcohol to loosen it because of the plastic construction around. Prying it off can cause tiny pressure marks on the compensation dial.

The red dot that serves as an index for the illuminator lever is made of rubber and is glued on. It can be easily removed with a pointed probe.

Be careful not to lose the loose brass pin in the center of the release-switch brass bushing.


2. Sequence to remove rewind-side top cover

The snap ring on the ISO dial cover plate can be most easily removed using snap ring pliers and tweezers. Here it is already removed.

Caution: the silver pivot pin for the crank release lever is loosely inserted and must not be lost.

To remove the rewind side top cover, the R2 lever must be moved to the down (on) position.


3. Sequence to remove bottom cover

The rubber cover, bottom is connected to a brass plate using double-sided adhesive tape.

With my F4, it was necessary to leave these two parts connected and remove the rubber cover together with the brass plate, as otherwise the rubber cover would break. The brass plate, in turn, sits on a green adhesive film.

As always, flux is required for the solder joints when desoldering the wires.

 

[Andreas Thaler]

4. Sequence to remove front-plate/mirror-box assembly

The four screws for the tripod socket base plate are secured with adhesive. Therefore, take care when unscrewing them so that the screw head profile is not damaged applying too much force.

Heat and isopropyl alcohol (applied alternatively) can loosen the adhesive; see here for more information (own contribution on Reddit). I had success using JIS bits on my cordless screwdriver.

The two rubber body covers are glued on and can be carefully pried off using a plastic spudger, for example.

This allows the seven wires in the access cutout, rewind side, to be desoldered.

The edge connector for AF FPC, bottom of camera, can be carefully levered out with the blade of a screwdriver. I use a plastic spudger with a wide blade, which I insert and rotate around its own axis.

When separating the front panel from the housing, proceed with caution and do not use force. It sticks a little at the couplings to the shutter and mirror box. With a little wiggling and patience, you will succeed.

The aperture control on the inside of the mirror box, release side is now accessible.

The flywheel (see arrow) needs one drop of light oil on its axle so that it can turn freely again.

The success can be checked by pressing the depth-of-field preview button several times. If the button can be pressed easily and there is no squeaking noise, the lubrication should be fine again. Doing this you can see the aperture control in action. One drop of oil on each of the other gear axles should not hurt.

This should allow the aperture to work correctly again.

 

[Andreas Thaler]

5. Sequence to remove shutter block

All necessary steps are described in detail in the SPT Journal, January/February 1993.

Once the front plate of the Nikon F4 has been removed, the shutter can be replaced.

The shutter must also be removed if you want to adjust it with full control.

To do this, open the front flex connector, which connects the shutter electronically to the circuit board. Then remove the rewind motor with the rewind gear and the rewind-coupling shaft. Now the shutter can be carefully removed from the housing.

To adjust the curtains-travel times

turn the two ratchet gears for the tension springs of the shutter curtains counterclockwise. This increases the spring tension and shortens the travel times.

The photo shows the ratchet gear for C1, the opening shutter curtain, marked in red, and the ratchet gear for C2, the closing curtain, marked in turquoise. The goal is to have both curtains run for the same amount of time.

Correct curtains-travel times?

The SPT Journal does not clearly indicate to me what the correct curtains-travel times are. Therefore, I assumed 2.67 milliseconds. This value is based on previous work.

If the target time is incorrect, the shutter speeds will also be incorrect. For example, instead of 1/2000 second, the exposure will be 1/1500 second. But that is less of a problem than if the shutter curtains run at different speeds. Then the film will be unevenly exposed.

Measuring the curtains-travel times on the camera tester

After each adjustment, I mount the shutter in a specially adapted F4 housing and measure the curtain travel times on the camera tester.

Charging the shutter.

Sequence for release of the curtains.

Since it takes some force to manually charging the shutter, I use my desoldering lever. Its shape and notch make it ideal for this task, as it does not slip.

When the F4 is mounted, the control electronics and the charge motor take over.


Shutter defective

After each adjustment, I took three measurements, which I noted down. Unfortunately, after the third setting, there was a problem with C2. The shutter curtain no longer triggered. I may have overstretched its spring.

I need to take a closer look at this and am therefore stopping. I consider the shutter to be defective and am not assembling the F4 at this time.


This is not a disadvantage for our project

We have already seen how to remove the front panel and oil the aperture control. Adjusting and replacing the shutter was just extra work.

 

[Andreas Thaler]

Note: The following text and photos are taken from my post Nikon F4: Mission Aperture Lever - two ways to fix the aperture problem.

The reason for this is that I am not reassembling the Nikon F4 in my current project because I want to investigate the problem with the shutter first. For our purposes, this is irrelevant, as reassembly always follows the same sequence.

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Reassembly of the Nikon F4

Details can be found in the Nikon F4 Repair Manual (pages A 45 - 47), also in various places in the SPT Journal, January/February 1993.

When connecting the front panel and the housing, 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 of the coupling 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 panel is inserted into the housing.

The front panel and housing are connected again.

With a little gentle movement back and forth, the front panel snaps into place.

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

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.

The F4 is reassembled in the reverse order of disassembly. Once all adjustment elements are back in place, it can be checked for proper functioning.

The aperture control should now work flawlessly.

When the shutter is released, the aperture lever in the mirror box should move all the way down without delay.


To check the aperture function:

1. attach a lens (AF or MF),
2. for an AF lens disable AF on the F4,
3. select manual exposure mode (M),
4. set the shutter speed to 1 second (or another value),
5. select the smallest aperture on the lens,
6. release the F4 and look into the lens from the front.
7. The aperture should close completely to the set value without delay.

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Conclusion

• DIY aperture control service on the Nikon F4 is feasible.
• We have seen the correct procedure here, which involves targeted oiling rather than pouring oil into the F4 in an uncontrolled manner. (See my post Nikon F4: Mission Aperture Lever - two ways to fix the aperture problem, which discusses both options in detail).
• Replacing the shutter is not a problem, but adjusting it can be difficult. I will take a closer look at this issue. Basically, I wonder whether high-performance shutters such as those in the F4 with 1/8000 second can be set precisely enough at all. According to the SPT Journal, the shutter was replaced with a new one when it no longer functioned properly. An exciting topic!

Please feel free to contact me if you have any questions

I wish you every success in your work!

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For more advanced aperture control service (if the method shown here is not sufficient), see

Nikon F4 Aperture Base Plate Overhaul Tutorial by Vladislav Stanimirović

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A word of caution

Please keep in mind that you’ll be using highly flammable solvents for service work, and their fumes are harmful to your health. Soldering also produces fumes that should not be inhaled. Dangerous high voltages can be present when handling electronics, especially in conjunction with electronic flash units and mains. Therefore, familiarize yourself with the safety regulations beforehand and ensure your safety. Depending on the activity, protective gear may be advisable.

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

Acknowledgments

Without the work of Master Larry Lyells, in particular, we wouldn’t have the detailed technical information we need today for service/repair of SLRs.

The SPT Journal and The Camera Craftsman, which he helped shape significantly as an author, and which contain all the necessary information and instructions are available for a fee through Learn Camera Repair.

We owe our access to them to Eugene Pate, the founder of Learn Camera Repair.