Leica R3 MOT ELECTRONIC: Heading into the unknown

[Andreas Thaler]

I will report here soon

Maybe the problem with your @miha R3 MOT is actually as easy to solve as shown in the video.

The following considerations based on what I saw yesterday when disassembling my R3 MOT:

In order to work in aperture priority, the camera needs information about the subject brightness, ASA number of the film and preselected aperture so that it can determine the associated stepless exposure time.

The R3 MOT measures the light value with the aperture open using the auxiliary mirror and the measuring cell in the mirror box.

The ASA number is set via a potentiometer (variable resistor) and the aperture preselected on the lens is also transmitted to a potentiometer via the aperture simulator ring and the cable.

These two potentiometers have gold-plated contact tracks over which wipers run. On the R3 MOT this is the construction under the ASA wheel, where the two ring-shaped potentiometers lie on top of each other.

The camera probably still works purely analog, which means that the light value, ASA number and aperture value are transformed into voltage values.

The two potentiometers do this for ASA and aperture value. Depending on the position of the wipers on the contact tracks, there are certain voltage values that the camera uses to calculate. This probably happens in the two ICs.

If the potentiometers have contact problems between the contact track and the wiper, this may be caused by oxidation, contamination or wear. I'm guessing the first two cases, unless the camera was heavily used, which should show. Irregularly occurring errors are typical for electrical contact problems.

This also explains why the times are ok in manual mode.

The aperture simulator is not needed here to build stepless exposure times because the times are fixed and called up.

Such potentiometers (variable resistors) with gold-plated contacts can also be found in the Minolta X-700, a successor to the Minolta XE-1.

I described how it works there:

Minolta X-700 electronics: A closer look

I'd like to take a closer look at the X-700's electronics in the coming days. On the one hand, I would like to understand how the circuit basically works, and on the other hand, I am interested in details that can be seen on the flexible circuit board. It's always fascinating to me what...

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Conclusion:

To solve the contact problems, it might be enough to just remove the left part of the top cover and spray electronics cleaner into the two potentiometers, without further disassembly. Then move through.

Very interesting, I'll see what technical information I can find in the service manual for the XE-1.

 

[Andreas Thaler]

Very interesting, I'll see what technical information I can find in the service manual for the XE-1.

If we rule out the other possibilities mentioned here for a defective exposure indicator, GREEN could actually be the cause of the problem with the measuring needle displaying incorrectly.

Because little should break in a camera unless it falls on the floor or is heavily used.

We will see.

 

[4season]

Is there any possibility of simply transferring the R3 top and bottom covers, plus mirror box onto a working Minolta XE-1

 

[Andreas Thaler]

Is there any possibility of simply transferring the R3 top and bottom covers, plus mirror box onto a working Minolta XE-1

Sure, you can do it with a hammer!

 

[Andreas Thaler]

I re-watched the excellent video on troubleshooting the meetering needle problem on a Minolta XE-1.

The process shown there can be transferred directly to the Leica R3 MOT, as the structure of both cameras is identical at the point shown. Only the left top cover and its attachment are designed slightly differently.

I will disassemble the left top cover, dismantle the unit underneath with the two potentiometers and clean it in detail. This is more precise than spraying electronic cleaner. I can also assess the condition of the wipers and contact tracks.

Next steps:

• Testing Miha's R3 MOT for general function and assessing the function of the meetering needle.
• Test run of contact cleaning on my practice R3 MOT, which I had already partially dismantled and reassembled for exploration.
• Cleaning the contacts of the R3 MOT from Miha with detailed documentation.
• Test and summary

With this procedure I want to ensure that the work goes smoothly.

If this does not solve the problem, the remaining option is to completely remove the top cover and clean all accessible contacts.

I hope that this will not be necessary; I have already described the associated problems and risks.

Stay tuned!

 

[Andreas Thaler]

And here is the repair of Miha's R3 MOT ELECTRONIC, based on the knowledge and experience gained previously:

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...

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