Leica R3 MOT ELECTRONIC: Heading into the unknown

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Andreas Thaler

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Here is my roadmap for this project:
  1. functional check
  2. error determination
  3. opening of the housing and orientation
  4. checking the circuit board and electromechanical parts (switches, contacts) as far as they are accessible
  5. parallel opening of an XE-1 for comparison (general observation, possible technical conclusions about the R3)
  6. conclusion
I decide whether I want to work directly on @miha R3 MOT when I have an impression of how easy or difficult the housing is to open.

Equipment for training is available, with this project I'm working on my R3 at the same time.

Stay tuned
 
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Andreas Thaler

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Disassembly of the Leica R3 MOT ELECTRONIC: Removing the top cover

Since I don't have a service manual for the Leica R3 MOT ELECTRONIC, but it is closely related to the Minolta XE-1, I compare the two cameras in order to have a guide for disassembly. For the XE-1 I have the service manual with an exploded view of the parts.

For comparison, I also have a Leica R3 ELECTRONIC, which appears to be identical to the Leica R3 MOT ELECTRONIC.

Instead of „Leica R3 MOT ELECTRONIC“ I will now use „R3 MOT“ for short.

The R3 MOT with some external injuries is from my inventory. I will test the individual work steps on it before I try on @miha R3 MOT.




From left to right:

Minolta XE-1, Leica R3 MOT ELECTRONIC and Leica R3 ELECTRONIC








The Leica R3 MOT (above) has connections for a winder/motor drive on the bottom cover.




Side view on the left:

All three cameras have a battery indicator light.







Front mounting screws on the XE-1 …




… and on the R3 MOT




The XE-1 (below) has two openings for attaching the compass tool. The R3 MOT above doesn't have that. The cap should be removable with friction.




The retaining screws for the rewind cranks.




The exploded view of the XE-1's casing parts (Minolta service manual for the XE-1) should also help when disassembling the R3 MOT.

Be careful with the winding lever because of the many individual parts.


Conclusion #1:
  • The Leica R3 MOT should be able to be opened with these considerations in mind.
  • With the top cover removed, most of the electronics should be accessible.
  • The next step is a functional test of the R3 MOT before disassembly to identify any further errors beside the jumping needle noted by @miha
This video mentioned above should also help you remove the top cover:



Stay tuned!
 
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Laurent

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Andreas Thaler said:
I think you're not yet at full capacity with your two current Canon projects!
Click to expand...
These are the "public" projects
The Pentax SV is parked on the side at the moment, as is the Kodak Hawkeye which needs lightproof bellows
 
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Andreas Thaler

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Since I was most worried about screwing the winding lever and I wanted to sleep well today, I started dismantling it.

I couldn't get any further with friction (rubber cylinder, rubber blanket), so I used pliers.

To avoid scratching the screw, I placed a piece of chamois leather around the screw. That worked.

However, I should have only used the pliers horizontally and not vertically because I slipped and there was a scratch. At least I was able to cover the botch with varnish.

There are several parts under the winding lever that can be put back together without any problems.

The first hurdle has been overcome, albeit with a points deduction









 
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Andreas Thaler

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Since I don't have a better tool to loosen such screws without causing damage, perhaps a piece of electrical wire could help me.

The wire is insulated with plastic and can be placed around the screw. The ends are then gagged and can be pulled with the pliers in the direction of loosening the screw. Damage is excluded.

Or the wire replaces the chamois leather as protection and the pliers are used again

I'll try that out tomorrow. Good thing I use my own camera for this
 

Laurent

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that's an interesting tip!
 
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Andreas Thaler

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With a lashed electric wire and pliers attached, the screw can be loosened without causing damage. The copper wire under the insulation protects against the sharp-edged jaws of the pliers.

However, this method remains risky and pliers with hard rubber inserts would be a better solution.

Maybe I can make something for myself.





 
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Andreas Thaler

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Removing the top cover

The top cover consists of three parts and can be removed after loosening some external adjustment elements and screws.

The part above the prism sits tightly over the circuit board and comes off after the bayonet ring is removed.





After removing the winding lever.




The rotary switch must be placed under this spring-loaded cam.




The dial for ASA and exposure compensation




The shutter speed wheel is held on its axis by three short screws.




The upper adjustment elements are removed.




The ASA indicator




The fastening screw for the main switch is located under a glued cover.




The front panel and left part of the top cover are removed.






After loosening two screws, the eyepiece cover is held in place by the rotary switch for the eyepiece shutter.




The screws for the bayonet ring can be removed easily.




This ring is inlaid only.




The inside of the prism cover with a piece of rotted foam.




All three parts of the top cover are now removed.




The mainboard
 
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Andreas Thaler

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Overview











A closer look at the electronic and mechanical components on the mainboard



The eyepiece is removed.




The small bulb for the battery indicator light.

Its switch above it is activated by the ASA indicator knob as soon as pushed. The contact should then close to ground via the pin on the right and the lamp lights up.




Trim pots




Wiring above the prism.

The arrow points on one of the two ICs found.




The right part of the board with contacts, switches, trim pot and IC #2.




The IC located on top of the prism.

Since the IC has no name, it will be a manufacturer-specific component for which no documentation is available.




The second IC on the right part of the board.

This IC also has no name.




The front part of the prism.

The shutter speeds, B, X and mode A are transparently displayed on the pane on the left and are reflected in the viewfinder.

In the middle is the tiny optics for the ADR window (aperture direct readout) for reflecting the aperture set on the lens into the viewfinder.




The light required for the pane comes in via a small window on the front cover.




The pane with the shutter speeds in front of the prism is connected to the shutter speed wheel via a cable. So both are synchronized.




There is also a cable pull attached to the ASA wheel.

I suspect that its remote station is a potentiometer in the prism range. So settings are transferred analogously.
 
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I cannot interpret the information on this plate.




Next to the frame counter is a blue tantalum capacitor.




All soldering points must have been set manually and look OK. Here, however, the connection is only loose.




The contact of the main switch located on the back of the R3 MOT.




The gold-plated contact track on the ASA wheel.




The exposure measuring cell is located at the bottom of the mirror box.




Above this is the main mirror with an auxiliary mirror attached to its back. The main mirror should be partially transparent. Part of the light entering through the lens is redirected to the measuring cell via the auxiliary mirror.




Overview
 

Laurent

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incredible mess of wires! The printed circuit board looks nice.
 
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Andreas Thaler

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Conclusion

A beautiful electromechanical camera and complex built, unfortunately without technical documentation. So troubleshooting is limited to general assumptions and suspicions.

Problems with the electronics over time could arise from oxidation on contacts in trim pots and switches. Here I rely on electronic spray, which cleans contacts and doesn't damage anything, see also below.

That's where I put my hope.


Next steps
  • I'm now cleaning and putting my R3 MOT back together. Only if that succeeds will I continue with the R3 MOT from @miha
  • Then I will have a look at the available information on electronics.
  • I don't have anything directly to the R3 MOT apart from the operating instructions. I hope I can glean something from the XE-1 service manual, even though the electronics are different.
  • Otherwise, there is a video that shows a fix for a jumping measuring needle in the viewfinder of an XE-1. Maybe this will also help with the R3 MOT from @miha (see below).
  • Otherwise I can only check the circuit board for any visible abnormalities.
  • Without a circuit diagram and information about how the electronics work, I can only try to make something if I'm lucky.
  • If the area under the mainboard is affected, it would have to be dismantled deeper. I don't want to get involved in that given the dense cabling.
  • I think it is unlikely that components will become defective over time. With an operating voltage of 3 volts, there is probably not enough power loss in the circuit to overload components.
  • The tantalum capacitor and ceramic capacitors should remain trouble-free.
  • I can treat switches and trim pots with electronics cleaner without changing their settings. Oxidation may have formed between their wipers and contact tracks.
  • Cold solder joints can be re-soldered.
  • If an IC is defective, a replacement from another R3 MOT could only be soldered in.


Stay tuned!


+++

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

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Amazing complexity! No wonder there are less and less camera repair guys willing to touch these 70s wonders.
 
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Andreas Thaler

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Further exploration before assembly



Before I assembled the R3 MOT, I wanted to take a look at the aperture simulator ring in the mirror box. It can be rotated and I suspected there were contacts underneath that I wanted to clean.

It wasn't possible to remove it, so I looked for the attachment for the mirror box to see if I could get anywhere.

To do this, the leatherette had to be removed, which was glued on very tightly.




There are two screws under the leatherette that belong to the mirror box.

The arrow points to the cam on the aperture simulator ring, which couples to its counterpart on the lens.




I discovered that the aperture simulator ring (red arrow) is connected via a cable (green arrow) to the place where the ASA wheel is located. I previously incorrectly assigned this cable to a potentiometer in the prism area.

When the ring was turned, the cable jumped out of a guide in the housing.






So I pulled the cable directly with tweezers to observe the mechanism. The cable pull turns a mechanism below the ASA wheel.

This is the point that is also shown in the video mentioned (fixing the jumping measuring needle in the viewfinder).

I wanted to take a closer look at this.




The gold-plated contact track of the ASA wheel can be seen.




There's a wiper running over it here.




But the ring with the contact track has another one on the underside on which a second wiper runs.

This wiper rotates via the cable with the aperture simulator ring in the mirror box. So this part belongs to the exposure metering system.








I also took off the leatherette on the right front of the housing to check the attachment of the mirror box here.

Here, too, the bond was very strong and there were remnants of a masking strip, which I removed with Zippo lighter fluid. This required some scraping.

Another fastening screw appeared under the spot.

But even after it was loosened, the mirror box remained stuck as if it had been welded on.

Therefore, I couldn't reattach the cable and also couldn't remove the aperture simulator ring for cleaning.




Under the bottom cover.


Assembly





I started by installing the eyepiece.

Here you can see the locking mechanism, which I activated with the pliers.
 
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Andreas Thaler

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The backside




To attach it, the eyepiece shutter must be pushed underneath here.




Two screws hold the unit in place.




The trigger that goes through the right top cover here.

Since the trigger is stiff, it should be cleaned.






The rotary switch for selective and integral measurement, which couples with its counterpart on the circuit board.






The main switch is in the off and on position. The contact behind it opens and closes.




The prism cover is stuck to this corner of the board and cannot be put on. It appears the cover is slightly warped.




And then it happened. The corner is broken off.

But it wouldn't be a problem to solder it back on and reduce it a bit.








Sequence of assembling the three-part top cover.




The main switch is installed.
 
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Andreas Thaler

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Likewise the rotary switch for the eyepiece shutter.




And the next accident that happened:

The spring-loaded insert ring is broken and part of it has broken off. This must have happened earlier when screwing on the bayonet ring.

The aperture simulator ring was also stuck, obviously I had overlooked something




The bayonet ring is now attached and everything works so far.

The detached cable is an exception




The front cover is in place.






The shutter speed dial can only be set in the correct position. This is ensured by the cam, which engages in a groove.




The ASA wheel with exposure correction and rewind crank is back on board.






With the installed winding lever the R3 MOT is complete, except for the leatherette, and can be triggered.

This ring remained. Does it actually belong to this camera?


Final conclusion
  • Since the cable is unhooked, the lens-aperture simulator coupling no longer works. In order to repair this, I would have to be able to remove the mirror box.
  • There will probably be problems when screwing in a lens because the inserted ring is damaged.
  • I also didn't solder the broken corner on the circuit board and
  • assembled the parts uncleaned.
Mistakes aren't nice, but in this case I'm not sad. I took apart my first Leica and learned a lot in the process.

The R3 MOT had already been damaged and worn down by the previous owner. Still, it would have been better if nothing had been damaged by me.

But it's better that I ruin my R3 MOT and not the one of @miha

That's what this exercise was intended for
 
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Andreas Thaler

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@miha you have now seen what I have done.

Please consider whether I should continue with your R3 MOT after this test run.

I don't think I'll make the same mistakes again, but who knows what will happen. At least I now have spare parts.

The R3 MOT is a solid and high quality camera that is built like a tank.

I suggest you find a repair shop that will not only fix the error with the measuring needle, but also do a CLA. I haven't looked at your camera yet, but since they're about the same age, a cure would certainly be good.

However, if you love risk, I'm there with the screwdriver
 

miha

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You have my full permission Andreas!
 
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