Minolta XG-M: Adjusting the shutter

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.

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


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

ic-racer said:

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.

Click to expand...

Thanks!

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

ic-racer said:

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.

Click to expand...

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

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:

Andreas Thaler said:

Thanks!

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

Click to expand...

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

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:





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).

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.

Andreas Thaler said:

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.

Click to expand...

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.

ic-racer said:

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.

Click to expand...

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

ic-racer said:

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.

Click to expand...

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

We'll see what we find.

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.

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.

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

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.

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.

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 …

Click to expand...

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

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.

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

Further work on this Minolta XG-M

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Dissection of a Minolta XG-M

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Introduction to the Reveni Labs Camera Tester

Andreas Thaler said:

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

Click to expand...

I did not realize! Good cameras to work with!

Another great thread!

ic-racer said:

I did not realize! Good cameras to work with!

Another great thread!

Click to expand...

Thank you, also for your valuable advice!

Andreas Thaler said:

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.

Click to expand...

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.