Minolta XG-M: Adjusting the shutter

[Andreas Thaler]

According to the SPT Journal, the XG-M can be set to two manual shutter speeds: 1/1000 s and 1/60 s, as well as Auto exposure:

I hope that the other shutter speeds then will also be correct.

 

[Andreas Thaler]

The picture shows the position of a thermistor on the circuit board, a temperature-dependent resistor.

Thermistor - Wikipedia

en.wikipedia.org

What could its purpose be, compensating for ambient temperatures to keep the circuit stable?

 

[Andreas Thaler]

Yes, usually counter-clockwise tightenes the springs in most cameras!!

Also, note that your RIGHT side, at 1.25ms, is not going to be affected much by the curtain tension. The readout is telling you the second curtain is being released 0.25ms to late.

Thanks!

I still have to find out which ratchet gear is responsible for which curtain.

 

[Andreas Thaler]

Also, note that the upper time limit for 1/1000 (per ISO 516:1999(E)) is 1.59ms, so the camera is OK by ISO standards.

This surprises me because I had adjusted the two ratchet gears back and forth without knowing what I was doing.

 

[ic-racer]

Sorry I made a mistake, the upper limit of 1.59ms for 1/1000 is for a temp. of zero C and lower.

For room temp, the ISO tolerance table is as follows:

 

[ic-racer]

Thanks!

I still have to find out which ratchet gear is responsible for which curtain.

The first (opening) curtain should be the one toward the back of the camera.

 

[Andreas Thaler]

Setting the curtain-travel times at a shutter speed of 1/8 s

Today I continued.

My goal was to set the two horizontal shutter blinds to a curtain-travel time of 12.4 ms each.

Since 1/8 s was the fastest shutter speed at which I could detect light passing through the shutter, I stuck with that setting.

Relax the two shutter blindes by opening the locking pawl.

To do this, I press it outwards with the screwdriver and the two ratchet gears turn until there is no more tension on the shutter blinds.

Now I can screw in both ratchet gears and increase the tension on the shutter blinds. The locking pawl engages gradually.

Thanks to @ic-racer for identifying the ratchet gears for C1 (opening shutter blind, closer to the back of the camera) and C2 (closing)!

To screw it in, I use a JIS Phillips screwdriver 000, which fits into the openings on the ratchet gears.

The XG-M is again supplied with power via cables with the removed battery unit.

Electronics technicians know the pitfalls of small crocodile clips. It is not always easy to open the crocodile's mouths because your fingers slip. This is even more so when the plastic insulation covers are pulled over them.

Electronics technicians' pliers with long, narrow jaws are very useful here:

Recommendation for pliers set for electronics and repair: Brüder Mannesmann

As a fan of good tools, I like to look at what is on offer. There are relatively few special tools for camera repairs, so electronics is a related field, for which there are tools in the right small size. I recently received this inexpensive set of electronics pliers from Brüder Mannesmann...

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Here you have to be careful that the connections via the crocodile clips do not accidentally short-circuit the battery.

The setup for measuring.

A first measurement result after I had turned the ratchet gears in by the same amount.

C1 (opening shutter blind) is too slow and C2 (closing shutter blind) is too fast.

Here I measured at a shutter speed of 1/2 s, since at shorter shutter speeds no more light passed through the shutter.

I'm not going to worry about the shutter speeds yet, first the two shutter blinds have to run at the right time.

The circlip pliers are a useful aid when pulling the insulation covers over the crocodile clips. It is easy to slip your fingers.

Here, the three connections on the circuit board are located close together.

It is therefore important that the crocodile clips are insulated from each other and the metal chassis via their insulation covers to avoid creating short circuits.

After a few attempts, I was able to set the curtain travel times for both shutters blinds close to the target of 12.4 ms.

In the next step, I'll take care of the shutter speeds, which are clearly too long for 1/8 s.

To do this, I have to go to the top circuit board of the camera under the top cover and make adjustments to the potentiometers.

It's not all that easy and anyone with the patience and love of an electronics technician will have an advantage

Today, for once, the table is not full

We‘ll continue tomorrow (CET).

 

[Andreas Thaler]

What I don't yet understand is why at shutter speeds of 1/15 s and faster, no light is visible through the shutter blinds.

This can only mean that the shutter blinds overlap when they run down and so no slit is formed.

On the other hand, the X-time for flash synchronization on the XG-M is 1/60 s, which is the shortest shutter speed at which the shutter is fully open (no slit formation).

This must also be the case for all longer times, so for 1/30 s and 1/15 s.

But 1/8 s is the fastest shutter speed where this works.

I may still need to adjust C1, but I suspect other problems.

Anyway, this is a teaching project and perhaps I had already messed up the shutter at an earlier point when I was tinkering with its mechanics.

What we will definitely do is check all the camera settings for voltage values (measurements on the circuit board with the multimeter) and of course adjust the shutter speeds. Larry Lyells gives detailed instructions for the former in the SPT Journal.

 

[ic-racer]

What I don't yet understand is why at shutter speeds of 1/15 s and faster, no light is visible through the shutter blinds.

This can only mean that the shutter blinds overlap when they run down and so no slit is formed.

On the other hand, the X-time for flash synchronization on the XG-M is 1/60 s, which is the shortest shutter speed at which the shutter is fully open (no slit formation).

This must also be the case for all longer times, so for 1/30 s and 1/15 s.

But 1/8 s is the fastest shutter speed where this works.

I may still need to adjust C1, but I suspect other problems.

Anyway, this is a teaching project and perhaps I had already messed up the shutter at an earlier point when I was tinkering with its mechanics.

What we will definitely do is check all the camera settings for voltage values (measurements on the circuit board with the multimeter) and of course adjust the shutter speeds. Larry Lyells gives detailed instructions for the former in the SPT Journal.

I was going to recommend getting just about any mechanical focal plane 35mm SLR (rather than electronic timed) to play with the shutter to get to know your new shutter tester.

With an electronic timed camera you can have weirdo stuff. Like on the SL35E that I work with, if the electronics are messed up, the second curtain releases at the same time as the first curtain. So no slit just as you are experiencing.

 

[Andreas Thaler]

I was going to recommend getting just about any mechanical focal plane 35mm SLR (rather than electronic timed) to play with the shutter to get to know your new shutter tester.

I got to know the tester with a Nikon F2 and a Canon F-1n, two mechanical champions.

With an electronic timed camera you can have weirdo stuff. Like on the SL35E that I work with, if the electronics are messed up, the second curtain releases at the same time as the first curtain. So no slit just as you are experiencing.

This is interesting, Larry Lyells covers this in the SPT Journal. Solder joints and IC problems.

We'll see what we find.

 

[Andreas Thaler]

I thought again about what the problem with shutter speeds shorter than 1/8 s could be.

Since I only made adjustments to the mechanics, the electronically generated shutter speeds should remain unaffected.

However, I removed the battery chamber and connected it to the camera via three cables in order to access the ratchet gears for the shutter blinds.

I think I need a fourth cable that connects the battery chamber and its mounting plate to the camera ground. When assembled, this is done by the plate - screws - chassis contact.

When ground contacts are interrupted, strange things sometimes happen in circuits.

We'll know more about this in a moment.

 

[Andreas Thaler]

Now it works, even the short shutter speeds are plausible

The green cable connects the holding plate for the battery chamber to the camera ground.

Now I will adjust C1 even closer to the default of 12.4 ms and see if the shutter speeds are OK.

 

[Andreas Thaler]

I have now set C1 and C2, I don't think I can do much more with the ratchet gears.

Both shutter blinds run at about the same speed at 1/1000 s, 1/60 s and 1/8 s and are close to the target of 12.4 ms.

In the next step I will therefore reinstall the battery compartment and see if I can set the 1/1000 s and 1/60 s using the associated potentiometers.

1/1000 s

1/60 s

1/8 s

 

[Andreas Thaler]

Installing the battery compartment

Tinning of the cable ends.

A cable that came off when removing the battery chamber is replaced with a new cable.

Soldering the cable to the battery chamber …

… and to the board.

Soldering the two contact bridges.

The battery chamber with mounting plate and tripod thread is reassembled.

I lost one screw, but the plate is firmly in place and is connected to the chassis, which also forms the ground, via the other screws.

I will look for a replacement screw in my stock later.

Quick test with inserted battery after assembly

The shutter works, here in BULB mode.

The base plate is screwed back on.

An interim test on the Reveni Camera Labs Tester.

The properties of the shutter have not changed.

Therefore, we can continue with dismantling the top cover in order to adjust the shutter speeds 1/1000 s and 1/60 s.

 

[Andreas Thaler]

Removal of the top cover

I won't describe the individual steps for removing the top cover here. They basically follow the other Minolta X cameras.

The parts pictured show their removal from left to right, with me removing the cover with the Minolta logo last.

The top cover is only connected to the circuit board via two cables, which I desolder. This gives freedom of movement.

Hot soldering irons and plastic don't mix

I'll fix that later with Sugru.


Setting the shutter speeds 1/60 s and 1/1000 s

Main switch to ON.

In addition to the shutter release, I also temporarily attach the winding lever.

I start by setting the shutter speed to 1/60 s. There is a separate trim potentiometer on the circuit board for this.

After a few attempts and finally tiny movements of the wiper with the slotted screwdriver, I hit the 1/60 s exactly.

Next we move on to the trim potentiometer for the 1/1000 s.

The shortest shutter speed always seems to be the problem child, as I have already noticed.

It doesn't get any better.

Perhaps I could improve it a little by adjusting the curtain-travel times of the two shutter blinds, but for our teaching project it's enough.

The actual shutter speed is closer to 1/500 s and the exposure of the film is uneven, as the deviation +0.60 EV for the left shows.

The question is how this affects results achieved by negative film and combined with editing in Photoshop in practice.

The shutter speeds 1/250 and 1/8 s are good/acceptable.

They are obviously adjusted automatically using the two trim potentiometers.

 

[Andreas Thaler]

Today, too, only a small setup on the table.


Further adjustments

Now I looked at other setting options and followed Larry Lyells in the SPT Journal:

Adjustment sequence

Manual inclination. Set 1/1000. Close S1 (by pushing release button part way) and measure the voltage between pin 14 of IC4 and the lead of thermistor TC that's closer to IC4 … Adjust for 180 mv with variable resistor C … in the Type S circuit.

The adjustment controls the linearity of the manual speeds. Although it's desirable to check the inclination voltage, adjustment is rarely required …

I measured 140 mV between IC and thermistor.

Using the corresponding potentiometer I was able to set the voltage to 182.5 mV, slightly above the target of 180 mV.


After readjusting 1/1000 s and 1/60 s I was able to achieve these values, which I am now happy with:

1/1000 s

1/250 s

1/60 s

1/4 s

 

[Andreas Thaler]

The XG-M is complete again, here with Data Back G by the way.

The shutter speeds 1/60 s towards longer shutter speeds are a bit longer after assembly.

Maybe it has something to do with the temperature in the room, which has risen, I'll take another look at it when it's cooler here.

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Conclusion

• Adjusting the shutter is not for the impatient but can be done with time and concentration.
• Some disassembly work and soldering is required.
• Working with the Reveni Labs Camera Tester is fun, operation is intuitive once you get used to it, I had no problems with the device during the numerous measurements.
• Perfection in the results is questionable in relation to practice. Slide film is most critical in terms of exposure, and the results cannot be edited. Whether the shutter is released at 1/60 s or 1/80 s should not play a special role if the time gradations are constant. Differently exposed areas of film are more critical.
• I will use the Reveni Labs Camera Tester to check my cameras to get an idea of which ones should stay in the closet and which ones are good for work. I will definitely not try to adjust every camera. It would be too much work.

+++

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

 

[Andreas Thaler]

Further work on this Minolta XG-M

Minolta XG-M: Shutter problem resolved but be careful

I checked the functionality of my XG-M to see whether replacing the four electrolytic capacitors was successful in the long term, see https://www.photrio.com/forum/threads/minolta-xg-m-replacing-the-electrolytic-capacitors.203831/ After a few releases, the mirror remained up and the LED...

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Minolta XG-M: Replacing the electrolytic capacitors

For my planning: Are you interested in how to replace the four electrolytic capacitors on a Minolta XG-M? In my opinion, many specimens are likely to be affected by leaking electrolytic capacitors, including damage to the surrounding conductor paths caused by electrolyte. I have an older...

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Dissection of a Minolta XG-M

Minolta XG-M: Dissection

I took a closer look at the inner workings of an abandoned XG-M for parts. So far good, every screw (almost only cross-Head screws) could be loosened with my JIS screwdrivers without cursing 👍 In one case - it was one of the longer screws for attaching the camera strap eyelet to the housing -...

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Introduction to the Reveni Labs Camera Tester

Reveni Labs Camera Tester: New perspectives for professional and private camera repairers

Professional test devices for analog cameras are usually only available from old stock. Their heyday is over with the switch to digital photography, their technology is clearly no longer state-of-the-art, but they are still used in repair shops. The devices were large and heavy and were...

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[ic-racer]

I got to know the tester with a Nikon F2 and a Canon F-1n, two mechanical champions.

I did not realize! Good cameras to work with!

Another great thread!

 

[Andreas Thaler]

I did not realize! Good cameras to work with!

Another great thread!

Thank you, also for your valuable advice!

 

[Andreas Thaler]

The shutter speeds 1/60 s towards longer shutter speeds are a bit longer after assembly.

Maybe it has something to do with the temperature in the room, which has risen, I'll take another look at it when it's cooler.

Today, at about 3 degrees Celsius lower room temperature, I checked the shutter speeds again.

1/1000 s

1/250 s

1/60 s

1/4 s


Nothing essential has changed.

I assume that the circuit for the magnets control is temperature compensated, the built-in thermistor suggests this.

With that, I will close this project.