Leica R3 MOT ELECTRONIC: Jumping metering needle repaired; front panel fixed with LEICA lettering

Andreas Thaler · Feb 10, 2024

miha said:
I might not recognize the camera anymore, it will not only undergone a brain surgery but a rejuvenation procedure as well

A thorough CLA would be good, cleaning the mechanics and lubrication.

To do this you would have to completely disassemble it. You can't pay for that in a workshop.

And if you do it yourself, maybe it could @88E30M50

He shows impressively that he has mastered complex calibers like the Canon A-1.

Andreas Thaler · Feb 10, 2024

Apart from that, the R3 is built like an historic battle tank:

Underneath the leather there is a solid metal housing, screwed on and absolutely nothing moves here. The covers are also made of metal.

You haven't built something like that for a long time.

I wouldn't know how to disassemble the camera; my attempt to at least loosen the mirror box on my practice R3 MOT was in vain.

The mechanics, which you can see through openings in the housing and above the base plate, are old class.

Andreas Thaler · Feb 10, 2024

A professional CLA would be justifiable for such a camera. Then it will work for another 50 years.

The discret analogue electronics are obviously durable, but anything that should fail can be replaced with current components. Except both ICs which can be found in other R3s.

The most common problem with the metering needle and automatic mechanism was contamination; perhaps a hard particle of dust between the wipers and the contact track had caused damage. But an exchange is possible.

A great camera

miha · Feb 10, 2024

Interesting. I think it could be comparable to something like Canon EF (a similar camera from the same period) but say a Nikon F3 should be a notch above build-wise?

Andreas Thaler · Feb 10, 2024

miha said:
Interesting. I think it could be comparable to something like Canon EF (a similar camera from the same period) but say a Nikon F3 should be a notch above build-wise?

The F3 is perhaps even more sophisticated and elegantly built mechanically, but in terms of quality I wouldn't say it's much higher.

The F3 does not have switchable integral and selective measurements with measuring cells on the prism and in the mirror box base. But the electronics are already highly integrated and take up less space.

With the R3 this sophisticated metering system is a huge effort in terms of construction, which is probably why there is so much wiring. The electronics for this are not yet highly integrated, so it requires the interaction of individual electronic components with mechanical ones. And that with very little space.

This should be a part of the electronic control for the two metering systems; the shifter for switching between integral and selective measurement is located there (see arrow):

miha · Feb 10, 2024

Thanks for the update, very impressive. Now I appreciate the camera even more. As for a professional repair service, I only know one who would still touch these old Leica reflex cameras (Paepke), but the costs would be higher than the value of the camera, of course if value is to be judged by its resale value. Or as Warren Buffett once said - Price is what you pay, value is what you get

Andreas Thaler · Feb 11, 2024

Andreas Thaler said:
View attachment 362589

The intact lamp is unsoldered from my practice R3 MOT ...

View attachment 362586

… and soldered into Miha's R3 MOT.

There is an error in the process.

Before replacing the bulb, I should have measured the voltage across its two contacts. So whether there is any voltage at all that makes it light up.

I was convinced that the filament of the original lamp had broken, and I had previously tested the function of my replacement lamp.

However, I re-soldered the two responsible soldering points and I couldn't have done anything more because the forward and return conductors disappear under the top cover.

Both cables looked good, no kinks or bare spots that could cause an open circuit or a short to ground.

In order to continue with this I would have had to remove the cover, and I didn't want to do that not to take any risks.

Anyway I remember: first measure, then solder

This can help save valuable spare parts.

Andreas Thaler · Feb 11, 2024

Fixing the front panel of the prism cover with LEICA lettering

The plastic holding frame behind the front panel with the Leica logo was broken and one of the two fastening screws no longer had a mating thread.

Therefore, @miha fixed the front panel with black tape. A solution that lasted 16 years

Anyway, the plate was slightly crooked and could be moved.

Today I wanted to see if it could be done without tape.

Removing the tape.

Adhesive residue

The broken holding frame for the front panel made of plastic.

On the upper side there are three recesses for small holding tabs in the panel.

On the bottom there are two threads for the screws, one of which is missing here.

Probably one of the few places on the R3 MOT where Leica (Leitz at this time) used plastic in the camera. Otherwise most of it is made of metal.

The inside of the front panel with the broken plastic thread below and the three holding tabs (red rectangle).

Remove adhesive residue from the tape above the bayonet ring with isopropyl alcohol.

Here too I cleaned with isopropyl alcohol.

I use the scalpel to remove any hard adhesive residue to get a smooth edge.

This has already been glued once.

I use the Spudger to spread the broken holding frame and apply Loctite adhesive.

Then I use the Spudger as a wedge that presses the holding frame against the cover while the glue dries within a few minutes.

The holding frame is now fixed.

I apply plenty of Pliobond to the holding frame and the inside of the front panel.

Whatever is too much can be easily removed afterwards without leaving any residue.

Apply on each part and let it dry briefly increases the holding power.

Since the left part of the holding frame is also loose, the recesses for the tabs in the front panel partially disappear under the prism cover.

I hadn't noticed this before when I put the front panel on as a test.

Now the upper part of the front panel does not close flush with the prism cover. The tabs get in the way.

Therefore, I mill off the metal tabs with the tungsten carbide cutter on the Dremel.

Now it should be fine.

Andreas Thaler · Feb 11, 2024

Second attempt with Pliobond.

What I applied previously makes a good base for the second coat.

This compensates for unevenness on the damaged holding frame, caused by old and hard adhesive residues

Now the front panel is in place.

Since the second screw no longer has a thread to screw in, I glue it in with Pliobond.

The remaining Pliobond can be scraped off with the Spudger and removed with tweezers.

I use acetone to clean the edge where the Spudger can't reach.

The acetone also removes hard residue from past adhesive attempts under the front panel.

I then remove fine streaks with isopropyl alcohol, Aqua Purificata and a dry paper towel (Kim wipe).

The result

The holding plate is now firmly in place and I let the Pliobond dry out.

I think the R3 MOT can now go back to Miha

+++

All information provided without guarantee and use at your own risk

miha · Feb 11, 2024

You improve everything you touch! Impressive work!

Andreas Thaler · Feb 11, 2024

miha said:
You improve everything you touch! Impressive work!

Ha, that would be nice, ask my wife

Andreas Thaler · Feb 11, 2024

Since the R3 MOT is going back to @miha in the mail tomorrow, I checked the exposure metering in aperture priority (automatic) mode again.

The two LR44 batteries that came with the camera and which I had intensively loaded with all the tests were inserted.

The displayed shutter speeds and the actual ones sometimes differed by ear from each other or were inconclusive.

A measurement of the batteries connected in series showed an open-circuit voltage of 3.02 volts.

The 3-volt lithium battery has 3.10 volts open-circuit voltage and is therefore fresher. With this battery everything worked flawlessly

So with this camera it is particularly important that the batteries are fresh so that the automatic exposure system does not get out of hand.

miha · Feb 11, 2024

Thanks for the tip. I guess silver oxide batteries, such as SR44, are even better choice.

Andreas Thaler · Feb 11, 2024

And should it ever be necessary to remove the front panel, this should be possible with careful leverage after having loosened the holding screw.

Pliobond lasts but is not as strong as Loctite.

Since the plate also sticks to the plastic holder, which is partially not fixed, I recommend removing the prism cover on which the front plate sits.

Andreas Thaler · Feb 12, 2024

Final observations with inserted a new 3 volt battery:

Automatic and manual settings work.
Sporadically the measuring needle went down two f-stops twice when pressing the shutter button and taking integral measurement, but I couldn't reproduce this.

I can't say what the reason for this could be, I know next to nothing about the circuit.

Since it is a purely analog system that is based on voltages and therefore also transmits signals as voltages, interference is possible:

For example, due to dirty or faulty contacts, as we saw here with the jumping measuring needle and the implausible shutter speeds.
Respectively the signals via contact tracks and wipers deviate from the target at a certain voltage because there is dirt or damage in a certain place that would otherwise have no effect.
Or an electronic component no longer conforms to the standard.
It can also be that current does not flow through the components but directly to ground, which means that the voltages in the circuit are no longer correct.

It's best to look at it pragmatically:

There are interferences in analogue broadcast and voice radio, in the old flashlight with light bulb or even when playing a record.

If they don't get out of hand, you can accept them.

Hopefully

miha · Feb 12, 2024

Well noted, and thank you.

Andreas Thaler · Feb 12, 2024

Andreas Thaler said:
Final observations with inserted a new 3 volt battery:

Automatic and manual settings work.

Sporadically the measuring needle went down two f-stops twice when pressing the shutter button and taking integral measurement, but I couldn't reproduce this.

I can't say what the reason for this could be, I know next to nothing about the circuit.

Since it is a purely analog system that is based on voltages and therefore also transmits signals as voltages, interference is possible:

For example, due to dirty or faulty contacts, as we saw here with the jumping measuring needle and the implausible shutter speeds.

Respectively the signals via contact tracks and wipers deviate from the target at a certain voltage because there is dirt or damage in a certain place that would otherwise have no effect.

Or an electronic component no longer conforms to the standard.

It can also be that current does not flow through the components but directly to ground, which means that the voltages in the circuit are no longer correct.

It's best to look at it pragmatically:

There are interferences in analogue broadcast and voice radio, in the old flashlight with light bulb or even when playing a record.

If they don't get out of hand, you can accept them.

Hopefully

While researching on the web, I read that the R3 (MOT) saves the measured value even with integral measurement as soon as the shutter button is pressed halfway.

With selective metering, the metering needle in the viewfinder falls down; with integral metering, it remains in the respective position on the shutter speed scale.

It would therefore be possible that the previously observed sporadic behavior - the metering needle goes down by two f-stops - still has no effect.

You would have to check it at 1/30 s, the difference to the shutter speed of 1/8 s can be clearly distinguished acoustically.

But as I said, I was only able to observe this sporadically.

Andreas Thaler · Feb 15, 2024

The problem with the measuring needle, which in aperture automatic mode with integral metering (sometimes) shows an exposure that is two f-stop longer as soon as the shutter button is pressed, continues to concern me.

I even found this interesting passage from Norman Goldberg:

Early CdS cells suffered from "memory" problems. If a cell was exposed to bright light for a few minutes, then pointed at a dimly lit scene, it would produce a falsely high reading. The converse was true, as well. The most reliable readings were made after "soaking" the cell for many minutes at the light level being measured. This problem has been greatly reduced in recent years.

Norman Goldberg, The Dark Side of the Lens, 1992

Since the Leica R3 also uses CdS photoresistors in its exposure metering system, this problem could possibly be an intentional measure. Namely a compensation for the „memory effect“ described.

To check the exposure metering across the entire shutter speed range, I pointed the camera first at a bright window for the fast shutter speeds and then at the dark wall in the room for the slow shutter speeds. The memory effect would be compensated for by a two f-stop longer exposure.

As a user of the R3 MOT, @miha may know whether this is true.

In any case, I trust the engineers of that time (1970s) to come up with such a solution.

It's a shame that there is no technical documentation for the R3, but maybe I can find something about it in the service manual for the related Minolta XE.

Andreas Thaler · Feb 17, 2024

I changed the title of the thread because the problem with the faulty aperture priority mode has not been solved.

@miha has tested his R3 MOT and is kind enough to give an update with video.

„And faulty aperture priority mode repaired“ is no longer valid in the title I therefore have deleted it.

But that's not the end of the matter for me, of course I'll carry on

miha · Feb 17, 2024

Andreas generously did the work and send the camera back to me. We've spoken privetrly already and he asked me to report back here in the forum. Due to age of the camera he did everything he could, even cannibalizing a donor R3 camera to get access to some of the needed parts. Upon inspecting the camera, I found the jumping needle has been fixed to perfection There are still limits to the CdS cells (more here: http://www.jollinger.com/photo/meters/other/beginners_guide.html )

However in Auto mode the speeds are not always correct = indicated shutter speed in the viewfinder (and these were correct based on light conditions and the F-stop / film ISO set) do not match those fired by the shutter. In the video the needle in the VF indicates something between 1/500 and 1/700 however when I fired 6 shots, only the second (possibly) and third shot seem correct, based on the visual judgement of the shutter and its corresponding sound. Shots # 1, 4 5, and 6 seem way too long:

http://gallery.leica-users.org/d/54...2_GALLERYSID=1fee651f405d8e53550015100fa510a7

The problem shows sporadically, in the video I was able to catch the most severe case. I've also noticed that while the camera is switch off, say over nigh, the problem always shows immediately in the first 10 or so shots, but if the camera is switched on for a longer period, it seems to somehow "stabilize" and the speeds are correct again.

In M mode, the camera works flawlessly though.

Oh, the tricks of the aging electronics

Andreas Thaler · Feb 17, 2024

Thank you @miha for taking time and trouble to test your camera!

I was of the opinion that the aperture priority function worked, at least by ear the shutter speeds seemed plausible or in accordance with the shutter speeds displayed in the viewfinder. But the video shows that the problem is not solved.

At least replacing the contact plate was able to stabilize the measuring needle, it no longer jumps around.

Apparently the problem with the automatic aperture has to do with age/use of the R3, it seems to occur frequently after years/decades according to reports on the web. Likewise with the related Minolta XE.

With a few exceptions (capacitors, older measuring cells), electronic components should not age. But contacts can oxidize and wear out, and solder joints can become unstable. There are a few options here in the R3.

In any case, I'll stay on the topic.

I have two R3s and two or three XEs here to work with.

The new Reveni shutter tester will be preordered today, which means I can then test validly from April/May.

Now the error hunt begins!

Andreas Thaler · Feb 17, 2024

On the psychology of DIY:

Of course, that would be a reason to give up, to be sad, to feel overwhelmed, to be disappointed, to revive the feelings of failure, inadequacy that you might remember from school, etc.

But all of that is useless in DIY and therefore doesn't even come on board.

What is not yet solved brings new experiences and insights

So I'm looking forward to what's next.

Maybe someone has ideas and suggestions to address the issue with faulty aperture priority?

Andreas Thaler · Feb 17, 2024

On the Public Relations of DIY:

In PR, failures are communicated as a prelude to even greater successes …

Stay tuned

Andreas Thaler · Feb 17, 2024

I am sorry @miha, it would have been nice if the problem had already been solved.

Andreas Thaler · Feb 17, 2024

miha said:
The problem shows sporadically, in the video I was able to catch the most severe case. I've also noticed that while the camera is switch off, say over nigh, the problem always shows immediately in the first 10 or so shots, but if the camera is switched on for a longer period, it seems to somehow "stabilize" and the speeds are correct again.

The Minolta X-700, a later successor of the, to the R3 closely related, Minolta XE, uses tantalum capacitors for the temporary storage of exposure values (transformed to voltages). I also saw such a capacitor in the R3 MOT. There may be a starting point here.

I'll see if I can find any information about this in the documentation for the Minolta XE.

Leica R3 MOT ELECTRONIC: Jumping metering needle repaired; front panel fixed with LEICA lettering

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