Minolta X-700: A renovation project

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Andreas Thaler

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Andreas Thaler said:


A little Ballistol silicone oil allows the parts to slide together without friction.
Click to expand...

I'm not sure if silicone oil is the right lubricant here as it creeps. But the amount applied should be too small for this. The alternative would have been light grease.

Anyway if there are any problems with the underlying contacts, they will be resolved quickly.
 
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Andreas Thaler

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Don‘t be screwdriver happy.

I always think about this advice from Thomas Tomosy.

Because repairs should only be carried out with the least possible effort. The more you disassemble, the higher the chance of changing something or not being able to reassemble it correctly.





This is about adjusting the coupling for the aperture simulator (source: Minolta Service Manual for the X-700).

At this point I had removed parts so that I could clean them. Assembly went without any problems, but is the adjustment correct now? I'll check that out.


It is a grave mistake to disturb the factory settings impulsively. In general, you should not disturb anything unless you’re absolutely convinced that that is where the problem lies.

Thomas Tomosy's statement refers to electronics, where there are trim potentiometers for settings.

But it applies to the entire system.

The factory settings, which do not change by themselves (unless the camera falls on the floor or the owner messes with it), will not be achieved again outside Minolta's defunct service workshops.

___

Thomas Tomosy, Camera Maintenance and Repair, Book 1. Amhurst: Buffalo, 1999
 
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Andreas Thaler

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I tested the camera with the 50/1.7 lens attached for viewfinder image and focus. This isn't a precise test, but everything seems plausible.

My findings so far are that the X-700 has been heavily used, exposed to moisture and dust for a long time, but has remained intact
 

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Repairs should only be carried out with the least possible effort. The more you disassemble, the higher the chance of changing something or not being able to reassemble it correctly.
Click to expand...
That is true - not only for hobbyists but even more for professional repairmen like me!
 
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Andreas Thaler said:
Next steps
  1. The next step is to dismantle the main switch to clean the contacts (ON/SIGNAL still does not work). Also I'm trying to make the associated switch in the top cover easier to turn. This switch couples with the main switch.
Click to expand...




Let's move on.

Today I was able to successfully complete both of these tasks


Main switch, cleaning the contacts



The main switch is located under this construction unit, which also includes the trigger and the time/mode dial.

It is a rotary switch with the positions ON/SIGNAL - OFF - ON. These settings are switched via wipers that run on contact tracks.




Position ON




Position ON/SIGNAL




Here the two wipers can be seen on their contact tracks.




In order to be able to test the function, the X-700 is provisionally rebuilt with ASA/Exposure Compensation Wheel left, trigger and winding lever.




Lo and behold, the power supply now also works via the ON/SIGNAL position

The contacts have obviously cleaned themselves through frequent movement.

Evidence that it is contamination/oxidation. I can help with electronics cleaner. It does not harm any materials, cleans and forms a protective film.




Sprayed twice into the opening above the contacts to the left and right. With the bellows I evaporate what is too much.




I move the switch left and right several times to aid the cleaning process.

Testing the function of the main switch, all three positions work

ON/SIGNAL remains silent because the piezo element that generates the sound is located in the top cover and is therefore not connected.






Since I have attached and closed the back panel, I can now also check the function of the image counter. Every time I wind the shutter it advances and when the back panel is opened it resets to „S“.

Everything fine here
 
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The corresponding rotary switch on the top cover: Increasing the smoothness of running




This switch couples with the main switch below whose contacts I cleaned earlier.

Its three positions ON/SIGNAL - OFF - ON each click into place. This should be done gently and effortlessly.

But it almost takes force to adjust it.




The switch cannot be removed, its metall retaining ring is crimped into the top cover.




But the tab that presses on the locking ball underneath can be unscrewed.

This design is also found on lenses where the aperture ring snaps into place.




The ball and screw are corroded and the surface of the ball is therefore rough.




Here you can see one of the locking positions for the ball.




I use some isopropyl alcohol to clean the area via the hole from dirt and old grease residue if present as best as possible.




Turn it back and forth, now the ring turns a little smoother. However, the ball is not placed yet.




I clean the parts in isopropyl alcohol.

This does not eliminate the corrosion but dirt and old grease residue if present.




The ball doesn't look fresh. It should be smooth and have a silvery shine.




Some silicone oil to lubricate the area via the hole.

I can't lubricate the entire ring because it sits tight and the oil would spread unintentionally to the surrounding area.




The ball gets extra silicone oil.




But despite all the love and efforts, the ball no longer feels like working and jumps under the table. A quick goodbye.

That's why I'm getting a replacement from an abandoned X-700.




The „new“ parts below look much better.

I therefore take over the complete set.




Assembled

And now the switch turns smoothly and easily as it should.




I'm doing another function test.

The camera now also works with ON/SIGNAL
 
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Here are the relevant passages from the Minolta Service Manual for the X-700 for today's session.

Stay tuned


Rotary switch on the top cover:






Main switch as part of a construction unit:




+++

All information provided without guarantee and use at your own risk.
 
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And the work continues


Replacing the temporary cable



The temporary cable was unsoldered and a new one was soldered in.

You have to be careful with the soldering tip because the contact on the right end of the cable is on plastic.

The original cable was thinner than this, but that's not a disadvantage. It would be different the other way around, as the cable cross-section determines the load capacity.


Cleaning the back door







Dirt, some corrosion, nicks




Cleaning in Durgol descaling solution diluted with water.




Carefully drying with the Dremel Versatip butane gas burner with an attached hot air nozzle.






This looks better now.




The nicks remain.




I clean the leatherette with Sonax foam cleaner.


Cleaning the case







I remove the corrosion area with the Dremel stylo and attached hard rubber polishing tip.






Refinish with Aqua Purificata and isopropyl alcohol. Where the Dremel cannot reach, the pointed probe removes corrosion residue.

The slight abrasion within the case is not a factor. It is important that the corrosion is eliminated.
 
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There is also corrosion (rust) on the base of the camera, which I remove as best I can with the Dremel stylo, the pointed probe and Aqua Purificata.


Cleaning the mirror











I blow off the mirror with the bellows and apply hydrogen peroxide 3 % with a cleaning swab, which removes the fungus immediately.

I treat the entire mirror with this and then remove the cleaning streaks with Zeiss lens cleaning fluid on a microfiber cloth.


Cleaning the eyepiece









I remove the eyepiece and clean the part of the prism behind it.
 
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Blow off with the bellows and clean several times with Zeiss lens cleaning fluid on a microfiber cloth.




The varnish on the side of the eyepiece is easily soluble, be careful.




Dirt and some corrosion that isn't stuck will come off with isopropyl alcohol.






Since I didn't remember how to insert the eyepiece, I looked in the service manual. The convex part therefore points outwards.




Assembled

There is a coating left on the eyepiece that I cannot remove. But it doesn't bother you when you look through it.


Cleaning the contacts







I clean the accessible contacts with electronics cleaner.




To avoid harmful electrostatic discharges, I wear a grounding bracelet that is connected to the work mat. This means that the camera and I are at the same electrical potential and no voltages can discharge.

Electrostatic discharges can be particularly dangerous for ICs.

This is only relevant if the camera is open and the electronics are exposed
 
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Cleaning the ASA/Exposure compensation wheel





To make it quicker, I put the parts in undiluted Durgol descaling solution. After about 20 minutes I rinse with water and dry.





I test the X-700 again to see if it works, everything is ok




How nice it would be if I didn't have to clean things up. But a kitchen remains a kitchen
 
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Next steps

The next session will be the finale, see remaining points 4 to 6:
  1. The next step is to dismantle the main switch to clean the contacts (ON/SIGNAL still does not work). Also I'm trying to make the associated switch in the top cover easier to turn. This switch couples with the main switch.
  2. I will also replace the temporary cable on the ASA/Exposure compensation wheel.
  3. Afterwards I will clean the case and the back door. Not to forget the mirror (fungus) and eyepiece.Since I don't want to work with liquids in the camera, I will remove the corroded areas using the Dremel Stylo with a brass wire brush. The dismantled ASA/Exposure compensation wheelcomes last, cleaning again with Durgol descaling solution and dishwashing liquid.
  4. The hole in the top cover that I created when milling the rusted screw head will be a cosmetic job. I'll close the hole with Sugru. This means there is no mounting screw for the top cover, but it will hold.
  5. Then I will measure the shutter speeds with the Photoplug. Or maybe @ic-racer will help me with one of his professional shutter speed testers
  6. If everything works, I'll mount the camera again.
  7. Renewing the light seals and the mirror shock absorber are a follow-up project. For this I first have to get suitable material.
Stay tuned


+++

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For information on the X-700 electronics see:

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...
www.photrio.com


Here, among other things, I take a closer look at the ASA/Exposure compensation wheel and the couplings for the aperture simulator and the program automatic.
 
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Closing the hole in the top cover; removing corrosion spots







The hole that was created when the screw head was milled out and areas of corrosion under the paint.






Here you can see a copper coating on plastic that is painted.

Corrosion spots on the inside of the top cover.

It is verdigris that forms on copper.








The corrosion must be removed sustainably, otherwise it may spread further.

I remove the spots with the Dremel Stylo with a stainless steel round brush attached.

Some material comes off the cover, which cannot be avoided.




The inside of the cover after processing with the Dremel.








Sugru is used to close the hole and reconstruct the sanded areas.

I now let it harden for 24 hours and then polish the surface smooth. Finally I paint over it with black gloss varnish.

More information about Sugru in camera repair can be found here:

Repair work: Sugru, the multi-purpose mouldable glue

For small repairs on cameras, I like to work with Sugru, a mouldable adhesive that can be kneaded and shaped. After hardening, it replaces plastic. https://sugru.com/ https://en.wikipedia.org/wiki/Sugru Here are two projects where I used Sugru. Alignment of a battery contact on a Canon...
www.photrio.com
 
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Andreas Thaler

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Measuring the shutter speeds with the Photoplug

I'm curious to see how precise the shutter speeds are in M(anual) and A(utomatic) mode.

The times should be precise as I am obviously the first to open the camera and there are no traces of work/tinkering inside.

Age and storage conditions should have no direct impact on electronically controlled shutter speeds, except in extreme conditions.

The Photoplug
  • can be connected to the smartphone either directly or via an adapter. I use an iPhone 11 Max Pro for this.
  • There is a light-sensitive measuring cell in the Photoplug, which measures the shutter speeds in conjunction with the associated app.
  • To do this, the Photoplug is held behind the film window with the back wall open, with the camera aimed at a light source.
  • You can then go through the shutter speed series and evaluate each individual measurement and save it in a list.
Let's take a closer look








To shield the Photoplug from ambient light that could distort the measurements, I build a light shield out of the bottom of a matchbox.




The Photoplug can now be placed safely on the film window of the camera, completely covering the 24 x 36 mm format.




As a light source I use my small light table for slides and negatives, which emits diffuse light at daylight temperature.

I put the iPhone on a box next to it and connect it to the Photoplug (unfortunately I can't take a photo of it because I take photos with the iPhone).




I start with a shutter speed of 1 second.

The app is started, the camera is triggered and then a curve is displayed. With two sliders you mark the start and end of a curve, which shows time and luminance intensity.

After you have set the target time, the app shows deviations in 1/3 f-stops. The measured values can then be saved in a list.

Not bad, the measured shutter speed only deviates by 1/10 of a second from the target time of 1 second. This means 1/3 aperture as a correction value that can be taken into account in the future.

It continues with shutter speeds up to 1/500, which is the maximum time the Photoplug can measure:















 
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A great result!

With one exception (1/250) the shutter speeds deviate from the target by a maximum of only -1/3 aperture value.

This doesn't matter with negative film, but I can correct the ASA number on the camera or use the exposure compensation (override) for it. But since there is one positive value, this is out of the question.

Here is an overview of all measured target shutter speeds, the actual values and associated correction values in f-stops (I read „1“ as „1/3“ as shown in the measurements).



Since I take photos with aperture priority,

I'm naturally interested in whether the camera sets the shutter speeds correctly here too.

With ASA 200 I set the aperture to f = 8 and read the automatically generated shutter speed in the viewfinder, which is 1/125 - 1/250.



The measured value is there. Since the X-700 sets shutter speeds continuously in aperture priority mode, it could also be 1/249.

But that doesn't matter for my practice with negative film, which has a wide exposure latitude.


More information about the Photoplug can be found here on the manufacturer's website:

Filmomat — PhotoPlug

www.filmomat.eu
 
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Excellent, the X-700 has survived the decades well, despite dirt and moisture

At the next - and final - session I'll finish the top cover (polish and paint repaired areas) and put the X-700 back together.

Then follows a detailed functional test and the usual conclusion.

Stay tuned!
 
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tjwspm

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I have a question because I also measure a lot with the Photoplug. Why are the peaks at the beginning and end of the exposure time displayed so differently? With some measurements - you can also see it in your last measurement here - the curve is difficult to evaluate because you can't see the peak values.

Then another note. I also measure 1/1000 s quite accurately and reliably with the Photoplug. By the way, this is an example where the peak values can be clearly seen (please ignore the f-stops as you cannot enter 1/1000 in the software):

 
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Honestly I don’t know. I am just happy that it works for me

Thanks for the tip about 1/1000! I hadn't even tried that.

@Filmomat

Maybe Lukas, the author of Photoplug, would like to chime in and explain the issue with the curves?
 
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Andreas Thaler

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For me the Photoplug is a great thing. It works accurately enough, is affordable, mobile and easy to use.

If the shutter speeds aren't right, I could try adjusting them. A trim potentiometer is responsible for this.

However, this is certainly not easy, as trim potentiometers react to even the smallest changes.

And @ic-racer recently mentioned, with reference to an article in an SPT journal, that it is an art to time the shutter curtains with each other.

This should be one of the reasons why professional shutter testers offer numerous setting options.

I would therefore have the X-700 adjusted for all other functions too in a workshop if I were to work with it.
 
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But it's great that the factory settings apparently last so long, 40 years.

What I'm learning from this is that this should also be the case with other cameras, unless they have been dropped, mistreated, or stored poorly.
 

tjwspm

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Andreas Thaler said:
Honestly I don’t know. I am just happy that it works for me

Thanks for the tip about 1/1000! I hadn't even tried that.

@Filmomat

Maybe Lukas, the author of Photoplug, would like to chime in and explain the issue with the curves?
Click to expand...

@Filmomat
What I learned from using Photplug is that just getting a shutter to work isn't enough. Only measuring afterwards shows whether the shutter has actually been restored well enough for photography.

By the way, I also use ShutterSpeed successfully in the reflective process, because with the Minox you can't reach the back of the lens, see

Measuring shutter speeds on Minox cameras

DIY device for Minox Shutter Speed measurements When offering used Minox cameras, the seller often states that the camera works because “plausible” noises can be heard at different times when the shutter is released. Aside from the fact that these noises can occur without the shutter even...
www.photrio.com
 

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tjwspm said:
Why are the peaks at the beginning and end of the exposure time displayed so differently?
Click to expand...

It's the rise and fall time of the sensor. As the exposure times get shorter, this rise & fall times get proportionally bigger. These rise & fall usually look like an exponential curve, which is very nicely visible in Andreas' plots.
 
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Andreas Thaler

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One could connect the Photoplug to a storage oscilloscope to see the curve in its entirety.

The question is whether the signal from the sensor - I assume it is a photodiode - needs to be amplified for this.
 

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Great work, Andreas, as always!
 
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