Nikon MD-4 Motor Drive: Issues with rotary switch and rewind resolved, cleaning

[Andreas Thaler]

The MD-4 on my table has been through a lot. It accompanied the F3 Press on which I replaced the exposure compensation wheel.

What's even more pleasing is that it works on the F3 Press and only has minor problems:

• The rotary switch around the trigger for setting the motor operating mode (L, S, C - Locked, Single, Continous) is stiff.
• Motor rewind seems sluggish and slow compared to other MD-4s.
• If no film is inserted, one of the red control LEDs lights up as soon as rewinding is activated. The engine does not start.
• Heavy dirt on the outside and probably also in the housing.

The rotary switch - a clever patience game, dedicated by Nikon's engineers

I know from dissecting an MD-4 that the rotary switch around the shutter button is made up of a few parts that are housed in the Motor Drive handle. These pieces are not easy to put together.

To access the switch, the back cover of the handle and the small circuit board with the control electronics must be removed.

Cover plate removed after loosening the four retaining screws.

Now the rear cover of the handle, which is fixed with two screws, can be removed.

After loosening two screws, the board can be carefully folded out.

Pay attention to the flexible conductor track, two cables on the motor and the metal tabs of a switch.

An adhesive strip that holds the conductor track on the inside of the handle is removed beforehand.

Everything is accommodated in a very small space.

Done!

The lower part of the handle, already removed from the motor housing.

It is only connected to the motor via the flexible conductor track.

The DC motor on its basis.

The damper all around is rotten.

I leave it as it is and make sure that no sticky crumbs come off it.

The translation of the engine power to the mechanical control of the Motor Drive.

The lubrication of the wheels is still intact, although it has already dried out a bit.

The rotary switch/trip unit dismantled.

It is now clear why the rotary switch is difficult to move.

Decades of dust and the opening in which it rotates is completly dry.

The dismantling work so far.

Sticky and dirty parts ...

... come to the obligatory Durgol descaling bath and are scrubbed with a brush.

... and are happy to finally be clean again.

The service manual shows what awaits me during assembly.

A little silicone oil allows the plastic rotary switch to slide smoothly back into its metal frame.

 

[Andreas Thaler]

Assembling the rotary switch unit.

The switch is inserted into the handle from above.

At the bottom there is a counter plate on a spiral spring, which is fixed with three screws guided through the rotary switch.

A game of patience that ultimately leads to success after several attempts.

The rotary switch is again attached to the handle.

The axis of the release button goes through the rotary switch and is fixed at its lower end with a small locking ring.

Using the blade of a flathead screwdriver, I press the locking ring onto the axle.

Completed!

The rotary switch is back where it belongs and now turns as smoothly as it should.

And it's clean too.

Now the handle comes back over the motor and is screwed to the housing of the Motor Drive.

The circuit board with the control electronics is already attached again under the rotary switch.

Without a magnetized screwdriver, I couldn't get the small screws into their angled positions.


Motor rewind check: Expedition to the motor gearbox and cleaning

To get to the mechanics, the housing must be dismantled step by step.

But first I would like to clean the space under the fixing screw for connecting to the F3.

Four screws hold the plate with the screw.

I lift the adhesive strip over the two screws slightly so that I can loosen the screws.

There is a rubber cover under the plate.

A real mess!

Swept and damp wiped.

The plate comes back into position and is screwed on tightly.

In order to open the case, some of the leatherette has to be removed.

There are numerous retaining screws underneath.

The leatherette is fixed with contact cement and can be removed carefully.

More dirt under the cover.

The dust and lint can be removed easily with a brush and blower.

Now the small viewing window above the image counter is clear again.

The next step is further removing of the leatherette and disassembling.

 

[Andreas Thaler]

A long fight with the two housing parts follows.

They are plugged into each other. It should be possible to separate them with a little leverage.

They do that as soon as I have discovered the last retaining screw that was hidden under the leatherette.

Circuit board with switches for rewind and switch for battery control (AA batteries or rechargeable battery).

Even in this state, the battery basket can still be inserted and the rewind process can be started.

So that I have a better view of the motor gear in action, I connect the motor to my laboratory power supply, which is set to 12 volts.

Details of the mechanics.

I can't figure out why the rewind is slow.

After much hesitation, I apply three drops of Nyoil to the gears.

Actually, the old grease should be removed first, new grease put in and the oil on the bearings.

But to do that I would have to disassemble the engine further.

I will not do that.

To do this, I would have to keep meticulous records of which part belongs where.

And I'm already too tired for that.

I would like to finish it today too.

I put the case back together.

The MD-4 is reassembled.

The complete set of leatherette is still left of the MD-4 that I dissected last year.

And it's already cleaned.

So I'm bringing these up.

And also used it to replace some of the leatherette that I damaged and then pulled off with pliers because I knew I had a replacement.

Above the set of old leatherette, below the new, clean one.

Attaching is easy with Pliobond contact cement.

Actually, you should paint the two contact surfaces, let them dry and only then connect them.

But it can also be done by simply brushing it on and pressing it on if the two levels are flat.

Wherever it's a corner, both surfaces are coated with Pliobond.

Press - holds.

 

[Andreas Thaler]

Here it is again, the MD-4.

But now clean and with a free-turning rotary switch.


By the way, I was wrong in my assessment that the motorized rewind was too slow or didn't work properly (red control LED).

The F3 Press has the MF-6 back cover, which has two contacts to ensure that the film is not completely drawn into the cartridge when rewinding.

With the film inserted everything works as it should.

Without film there is obviously no rewinding - unlike the common F3 versions.

So I could have saved myself the disassembly.

But that made sense, because now the MD-4 is a lot cleaner inside.

Ready for service


+++

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[mshchem]

Fascinating. I recently retrieved some 10-32 1/4" hollow head set screws for a Beseler lens turret, it was a bit of a shaky job but I managed to get these in. .

 

[mshchem]

 

[Andreas Thaler]

View attachment 355525

Say hello to your beautiful sister!

 

[Andreas Thaler]

Follow up see

Nikon MD-4 Motor Drive: Operating mode selector switch fixed

This post follows up: https://www.photrio.com/forum/threads/nikon-md-4-motor-drive-issues-with-rotary-switch-and-rewind-resolved-cleaning.203356/ When I checked the motor drive, I saw that the attached Nikon F3P fired continuously not only in C(ontinous) but also in S(ingle) mode. That...

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