Nikon MD-4 Motor Drive: A dissection

I wanted to know exactly and dismantled my practice MD-4.

Actually, at first I was only interested in how I could remove the battery contact plate in the battery compartment. Another MD-4 has traces of corrosion at this point that I cannot satisfactorily remove from the outside.

And then I wanted to see what the switch for the two LEDs looks like as a battery tester. It doesn't work in the other motor drive. At least I assume so.

What followed was a


Hard fight

Despite the service manual and exploded drawings, I had to fight my way through, screw by screw.

The motor drive is really interlocked, a fortress made of metal and only few plastic.

Ultimately, I managed to completely disassemble it.

This is what an MD-4, the system engine for the Nikon F3, looks like.

Here without the MS-3 battery holder inserted:




Disassembled and on the way to cleaning in Durgol descaler solution:




The parts:




Details:












The three-part housing.

A sturdy metal chassis:














I cleaned the two transmission parts with lighter fluid and cleaning swabs as best I could without dismantling the movements.

Old lubricants had to be removed from corners and sprockets.

Also a piece of rotten adhesive tape that was stuck near the counter disk.

Loosening a screw and using a pointed probe to pull it out helped here:




Conclusion:

• The battery contact plate basically sits in the citadel. Almost unattainable.
• The battery check switch is easier to access, at least partially. But it also only reveals itself after almost complete dissection.
• The three-part housing that is screwed together appears indestructible. Metal, like an armored beetle.
• The motor gear is also made entirely of metal. Even heavy contamination did not prevent it from running freely.
• The circuit board has a rubber cover, which can be seen in the overview image at the bottom left.
• There is an IC on the circuit board that is not further documented in the service manual. A black box that takes care of controlling the motor drive in cooperation with the electronics of the F3.
• The DC motor is sealed, maybe I can still crack it.
• The leatherettes cover several screws and are glued. Glue is required to reattach.
• Overall, I am once again blown away by the technology, value and durability. I have several MD-4s in my collection, even the most worn-out ones do their job just fine. When the device does not function, the battery contacts are often corroded by battery acid - a user error.
• Probably one of the best and most reliable camera motors - I would say.

Looking at the cleaned parts is now a joy:












There are three switching positions for the trigger:






1. OFF - the two metal contacts of the switch for activating the exposure metering system are separated (see arrow):




2. ON - exposure meter on:

When pressed slightly, the contact closes and the exposure measurement is switched on:




3. ON - Trigger:

Further pressure activates the second release switch.

This results in the familiar quiet clicking sound.

There is a contact in the black switch housing that, when pressed, snaps against a second contact - click!

The electronic signal transmission from the motor drive to the camera occurs via resilient pin contacts in a ring.

The pin contacts in the ring and the mating contacts on the underside of the F3 couple when the camera is placed on the motor drive:






The ring can be removed from the circuit board after loosening two screws:




Be careful, the inserted coil springs are prone to jumping:




The springs in the ring electrically connect the pin contacts to the circuit board:






The MD-4 has two red control LEDs on its back.

By pressing a button next to it, the status of the battery voltage can be checked.

The LEDs also light up when the film is being transported, when the end of the film is reached or in the event of a fault:




Here the LEDs are removed, the push button on the right, parts of the mechanical switch on the left and in the background:




If you would like to set the trigger of your MD-4 softer or harder, you will find instructions in the service manual on page 128 (numbering document).

There is also information about the circuit and details there:

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This completes the dissection and study of parts and system.

I can only bow to Nikon's engineers.

The combination of precision mechanics and electronics in a small space is fascinating.

Designing a complex, fine electromechanical system so that it works reliably for decades, even under harsh conditions, is a masterpiece.

Helpful for studying individual parts and for guidance on repair projects:




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