Leica R3: Mission Aperture Priority

[Andreas Thaler]

The Minolta XE-1 (XE, XE-7) is discredited because its electronics become unreliable over the decades.

Known symptoms are a jumping metering needle in the viewfinder and incorrect shutter speeds in aperture priority mode.

Solid, fascinating technology, beautiful, but with problems: Minolta's XE-1 (XE, XE-7)


I can confirm both from my own experience; it also applies to the closely related Leica R3.

The problem with the metering needle can be solved:

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

Today I unpacked the Leica R3 MOT ELECTRONIC that @miha sent me some time ago for an attempt to repair. After practicing on a well-worn R3 MOT for the last few days, I felt sufficiently prepared to get to work. See the story here describing all the technical details and guesses where the...

www.photrio.com

See also video below.


The problem with the aperture priority mode is still waiting for a solution.

To move forward here, I have acquired several XE-1 that I will be checking for these errors and try to repair.

The aperture priority mode of the XE works with a


Sophisticated memory system

In order to be able to hold the measured exposure values before folding up the mirror, the camera stores them as charges in tantalum capacitors.

Here it could be that the capacitors are no longer in the norm and therefore deviations occur in the automatically formed shutter speeds.

Suitable capacitors are available and perhaps replacing them will provide the solution or at least new insights.


Next steps:

• Remove the top cover from the Minolta XE-1.
• Remove both circuit boards.
• Measure the three built-in capacitors and
• definitely replace them.
• Check whether the replacement of the tantalum capacitors achieved anything.
• If so, I can transfer the knowledge gained also to a closely related Leica R3.

Mission Aperture Priority starts tomorrow Monday (CET).

Stay tuned as always

---

Minolta XE - Wikipedia

en.wikipedia.org

Minolta XE-1

The mid 70's saw the birth of Minolta's first auto-exposure enabled SLR, the Minolta XE-1. This is undoubtedly a nice looking camera. It m...

tinkeringwithcameras.blogspot.com

 

[Andreas Thaler]

As always, any experiences and observations regarding these issues are helpful, perhaps someone would like to share briefly.

 

[forest bagger]

As always, any experiences and observations regarding these issues are helpful, perhaps someone would like to share briefly.

It's commonly known that tantalum capacitors go weak over the years.
Mostly they develop shortcuts or leakage, but a changed capacity is possible, too.

 

[Andreas Thaler]

It's commonly known that tantalum capacitors go weak over the years.
Mostly they develop shortcuts or leakage, but a changed capacity is possible, too.

Thank you, that gives me hope!

The three tantalum capacitors should be relatively easy to reach; they are located on the underside of the two circuit boards (on the prism and on the top right of the camera).

It should definitely be an error that occurs over time, i.e. an aging process, since the XE worked at the beginning.

I don't know what else could be aging in the circuit. There are no electrolytic capacitors installed and I think it is unlikely that soldering points will get cold at a certain point.

 

[Andreas Thaler]

Unfortunately, my two Minolta XE-1s are not suitable for this project.

In one the mirror stays up, in the other the shutter releases with only one exposure time and the metering needle in the viewfinder does not move.

That's why I'm trying my luck with the three Leica R3s that I still have here. So I'll change the title accordingly.

 

[Andreas Thaler]

And here is our candidate:

An R3 MOT ELECTRONIC with a jumping metering needle and only one working shutter speed.

I'm guessing defective capacitors.

On my practice R3 I will look at where the capacitors are and how I can get to them.

Hopefully the tantalum capacitors I already put away for the Minolta XE-1 will fit.

We will see.

 

[Andreas Thaler]

Tantalum capacitors in the Leica R3 MOT

Today I went looking for tantalum capacitors in the Leica R3 MOT.

Following the closely related Minolta XE, I expected to find three tantalum capacitors responsible for the memory system. With this system, the camera temporarily stores measured exposure values in automatic mode.

I suspect that a failure or partial failure of these tantalum capacitors leads to the well-known problems with incorrect shutter speeds in automatic mode.

Once it is known where these capacitors are located and what their electrical values are, a replacement can be made with new capacitors that are commercially available.

Since I don't have a service manual for the camera, I examined my partially dismantled R3 MOT, from which I had taken the contact plate for the R3 MOT from @miha to replace it.

---

A blue tantalum capacitor sits on the bottom of the right circuit board.

To the left of it is a diode, which is also cast in a teardrop-shaped housing, but is colored yellow-black.

There is a ceramic capacitor behind the tantalum capacitor on the right.

The two soldering points for the tantalum capacitor are located in this area (red circle) and are built over.

After loosening a screw the area can be exposed.

The cable harness, which is attached to the circuit board with a now rotten foam, can be lifted and pushed aside slightly.

Now the tantalum capacitor can be unsoldered.

The red circle marks the two soldering points.

With desoldering braid and flux, desoldering is quick and clean. The capacitor then only needs to be pulled out of both holes.

It is important to note its polarity, as the connections must not be mixed up when soldering in the replacement part.

It is a 0.1 uF/35 volt tantalum capacitor.

The plus sign indicates the positive connection.

My electrolytic capacitor meter cannot measure this small capacitance, it is beyond its measurement limit, which starts at 0.3uF.

Therefore I ignore the ESR value, which is too high here.

The component tester can determine the capacitance of the capacitor, but not its ESR value, which allows conclusions to be drawn about its condition.

The measured capacity agrees with that stated.

I suspect one or two more tantalum capacitors on the underside of the board on the prism.

I loosen the mounting screws on the circuit board and carefully fold it up against the numerous cables above it.

And here is one.

The two soldering points of the capacitor are on the top of the board in this area.

Desoldering without first exposing the crowded area is hopeless.

But that's not a disadvantage.

I use the side cutters to separate the capacitor from the circuit board.

A new capacitor can be soldered onto the remaining remnants of its connections.

The electrical values of this tantalum capacitor are 1.0 uF/25 volts.

My measuring device can record this capacitance value.

The stated and actual values match. The ESR value is also ok.

 

[Andreas Thaler]

I can't find a third tantalum capacitor.

To be sure, I would have to dismantle both circuit boards, but as far as I can illuminate the areas underneath, there is none left.

---

Conclusion

• The R3 MOT obviously has two tantalum capacitors, one less than the closely related Minolta XE.
• The two capacitors are relatively easy to access and can be replaced without much disassembly. They can be replaced with equivalent ones from new production. These are no manufacturer-specific components. The electrical values must match.
• Soldering in should be easy.
• When soldering, it is important to pay attention to the correct polarity.
• An attempt to repair a R3 MOT will soon show whether the problem with automatic operation can be solved by replacing the two tantalum capacitors.

Workplace and tools used today.

Stay tuned!

 

[Andreas Thaler]

The component tester can determine the capacitance of the capacitor, but not its ESR value, which allows conclusions to be drawn about its condition.

The measured capacity agrees with that stated.

Vloss should be the voltage loss in the capacitor within a certain period of time. A measure of how well the capacitor holds its charge - and therefore its voltage.

The value displayed seems good to me.

By the way, the component tester can also determine the ESR value, but the capacitance value may also be too small for this.

 

[Andreas Thaler]

@miha reported that his camera's automatic function worked again a few minutes after turning the camera on.

A temperature-dependent resistor that is installed on the circuit board above the prism could also play a role here.

It is an NTC thermistor that loses resistance as the temperature increases and therefore conducts better.

I assume it's there for temperature compensation in the circuit, but I don't know any details about it. But if it is defective, that could have an impact.

Otherwise I wouldn't know which components could lose their target values after decades, more or less at the same time.

 

[Andreas Thaler]

I also suspect the trimming potentiometers, there are a few of them in the R3 MOT.

Oxidation may change the contact properties over time and the contacts then conduct unreliably. Sometimes better, sometimes worse, like a cold solder joint.

This would explain the confusion with the shutter speeds in automatic mode.

It will be about cleaning the contact on the potentiometer between the wiper and the resistance track.

---

A trimming potentiometer for permanently adjusting voltages in a circuit:

The blue arrow points to the resistance track, the red arrow points to the wiper.

If you rotate the wiper, the distance that the current has to travel across the resistance track increases or decreases. As the resistance track is a resistor this also changes the voltage values that drop across the contact path.

If the contact between the wiper and the resistance track is disturbed, for example due to oxidation, this can disrupt the flow of current and therefore the voltage values.

This means that the voltage specifications in the circuit are no longer correct and malfunctions occur.

---

It may be enough to turn the wiper back and forth a few times to improve contact. However, these potentiometers are probably still at the factory setting and even small changes to the wiper settings can cause further deviations and make things even worse. So I'm going to try my luck with an electronics cleaner that works on its own.

It would also be possible that there are cold solder joints. But that would have to affect many of the R3 and XE, and I think that's unlikely.

I don't think the two ICs in the R3 are suspicious; they should be resistant to aging.

And apart from a few SMD components covered with varnish and a transistor, there is actually no other electronics to be seen.

Then I can't think of anything else.

 

[forest bagger]

Hi Andreas,

the "contact track" is made of non oxidateable material, the "wiper" usually cleans itself during wiping.
But the riveted contacts on the "contact track" are known for problems...

 

[Andreas Thaler]

Hi Andreas,

the "contact track" is made of non oxidateable material, the "wiper" usually cleans itself during wiping.
But the riveted contacts on the "contact track" are known for problems...

Thanks!

The term I used „contact track“ is incorrect, it should be called „resistance track“. In German it is called „Widerstandsbahn“. I have changed my posting above accordingly.

I'll treat the pots with electronics cleaner, I can't do anything more anyway.

 

[Andreas Thaler]

Hi Andreas,

the "contact track" is made of non oxidateable material, the "wiper" usually cleans itself during wiping.
But the riveted contacts on the "contact track" are known for problems...

Michael, do you have any idea which electronic components change their electrical values after decades, pretty much at the same time?

All I can think of are the tantalum capacitors, the pots and the thermistor (?).

 

[forest bagger]

I'd look for the ceramic capacitor first you found there.
Sometimes these make a kind of a short circuit.

 

[Andreas Thaler]

I'd look for the ceramic capacitor first you found there.
Sometimes these make a kind of a short circuit.

Thanks, I tested that too, the capacity is correct.

Here, on the right in the picture, is another larger capacitor with 1 uF, which I also tested.

I'm guessing this is a film capacitor?

 

[forest bagger]

capacitor with 1 uF, which I also tested. I'm guessing this is a film capacitor?

A film capacitor with forehead contacts.
Is usually durable.

 

[TPrins]

And here is our candidate:

View attachment 363908

An R3 MOT ELECTRONIC with a jumping metering needle and only one working shutter speed.

I'm guessing defective capacitors.

On my practice R3 I will look at where the capacitors are and how I can get to them.

Hopefully the tantalum capacitors I already put away for the Minolta XE-1 will fit.

We will see.

Hey Andreas, i got exactly the same problem. No jumpy needle, but the same shutter speed all over the dial. It's the mechanical shutter speed.
I've got another R3 and if i take the batteries out, it shoots at the same speed all over the dial too. So my guess was that it's not getting any power, but the funny part is that when i turn the camera on, the lightmeter works perfectly. I've checked the pcb and ceramics for cracks, cleaned everything with isopropyl but no luck. I see you're replacing capacitors and i'm curious if you had any luck in fixing it. Could it be the magnet?

 

[Andreas Thaler]

Hey Andreas, i got exactly the same problem. No jumpy needle, but the same shutter speed all over the dial. It's the mechanical shutter speed.
I've got another R3 and if i take the batteries out, it shoots at the same speed all over the dial too. So my guess was that it's not getting any power, but the funny part is that when i turn the camera on, the lightmeter works perfectly. I've checked the pcb and ceramics for cracks, cleaned everything with isopropyl but no luck. I see you're replacing capacitors and i'm curious if you had any luck in fixing it. Could it be the magnet?

I haven't bothered with it for the time being in favor of other projects. But I believe that this is a capacitor problem.

As far as I know, these capacitors store exposure values as charges, which correspond to a respective voltage.

The related Minolta XE-1 has a similar problem.

So you could check or replace the existing tantalum capacitors.

But that's just a guess, because such capacitors are not actually known for series failures, unlike electrolytic capacitors.

You would have to take a closer look at the circuit. The board is densely packed with discrete electronic components and wiring. Contact problems could also be a cause.

But these are all just assumptions, not verified.

 

[TPrins]

I haven't bothered with it for the time being in favor of other projects. But I believe that this is a capacitor problem.

As far as I know, these capacitors store exposure values as charges, which correspond to a respective voltage.

The related Minolta XE-1 has a similar problem.

So you could check or replace the existing tantalum capacitors.

But that's just a guess, because such capacitors are not actually known for series failures, unlike electrolytic capacitors.

You would have to take a closer look at the circuit. The board is densely packed with discrete electronic components and wiring. Contact problems could also be a cause.

But these are all just assumptions, not verified.

Thanks for the crazy fast reply! I'm suspecting the caps too, it's just that these barely fail. To get to the magnet is a bit more tricky, so maybe i should start with the caps. I've seen you've taken them all out, which would you expect to fail first?

 

[Andreas Thaler]

I'm suspecting the caps too, it's just that these barely fail. To get to the magnet is a bit more tricky, so maybe i should start with the caps. I've seen you've taken them all out, which would you expect to fail first?

I don't see any connection between the magnet as a switch and the problems with the incorrect exposure times.

The magnet opens or closes and is controlled by the electronics, so it is subordinate.

Since I don't have a service manual for the R3 (?), I wanted to look at the one for the XE-1. This generation of cameras was explained in more detail, and there are also details about exposure control there.

 

[TPrins]

Cleaned the magnets first. I took the front of, without unsoldering any wires and gave the magnets an isopropyl alcohol clean. Working shutter speeds again! All manual speeds work fine now, except auto. With the needle at 1/500 its firing at 3+ secs for example. Always taking very long, and occasionally just firing at a higher speed. So still suspecting the caps. Next mission is identifying those caps, in order to replace them. There's no marking on it, as far as i see. @Andreas, any clues? You've taken them out right.

 

[Andreas Thaler]

All manual speeds work fine now, except auto. With the needle at 1/500 its firing at 3+ secs for example. Always taking very long, and occasionally just firing at a higher speed. So still suspecting the caps. Next mission is identifying those caps, in order to replace them. There's no marking on it, as far as i see. @Andreas, any clues? You've taken them out right.

Unfortunately not, you are ahead on this topic.

Please keep us updated

 

[Nimbus62]

Hi,
In case bad automatic speed and good manual speed, take a look at the A/M Switch.
On the R3 the electronic is exactly the same than Minolta XE, same IC, same printed board. The difference is in the additional cell and cell switch: Spot / Integral.
If you have good manual speed, the main cap are OK (used in manual and auto).
The memory cap C1 is a MKP then no chance to be faulty.
Check the A/M switch S7 (same location as the XE). You can check voltage on pin 6 of IC1 (have to activate the electronic pressing the shutter commande halfway).

I build the electronic shema and it is available on my drive.

Leica R3 - Google Drive

drive.google.com

Hop it will help you.

 

[Andreas Thaler]

Hi,
In case bad automatic speed and good manual speed, take a look at the A/M Switch.
On the R3 the electronic is exactly the same than Minolta XE, same IC, same printed board. The difference is in the additional cell and cell switch: Spot / Integral.
If you have good manual speed, the main cap are OK (used in manual and auto).
The memory cap C1 is a MKP then no chance to be faulty.
Check the A/M switch S7 (same location as the XE). You can check voltage on pin 6 of IC1 (have to activate the electronic pressing the shutter commande halfway).

I build the electronic shema and it is available on my drive.

Leica R3 - Google Drive

drive.google.com

Hop it will help you.

Great, thanks!

Unfortunately I can't access the file, could you send it via PM?