Repairing a Minolta XG-9 camera

This is the story of how I repaired, broke, and repaired again a Minolta XG-9 35mm SLR film camera.

It will be long, and of niche appeal, but I’m writing it up in case anyone else finds it as useful as I would have done before I started. Here’s the plot summary:

  • The camera’s shutter was sometimes sticking open when fired in Auto mode
  • I set out to fix this by cleaning the electrical contacts of the film-speed selection switch, beneath the camera’s top plate
  • That appears to have been the correct fix, but when reassembling the camera, I broke a fragile plastic part which holds the power switch in place, rendering the camera useless
  • I modelled a replacement part using 3D modelling software, had it 3D printed, and replaced the part in the camera
  • The replacement part is good enough to use, but could probably have been better; I’ve published the model for it, and would appreciate any ideas

If that sounds in any way interesting, read on. This was my first attempt at repairing a camera and my first experience of 3D modelling and printing, so it was certainly interesting to me.

The original problem: a sticking shutter

OLYMPUS DIGITAL CAMERA

The camera is one that I wrote a happy post about last year (“A film camera“). It was made in 1980 or so, but I bought it in 2018.

It worked well, except that the shutter would sometimes stick open when fired in Auto mode, and the only way to close it was to switch out of Auto. When stuck open, it often let in enough light to ruin both the previous and following photos as well as the current one. I was keen to fix it, especially as these cameras are designed so that the light meter only works when in Auto mode.

The first hint I found online was here, in a photo.net post from 2003 by “rokkor fan” who writes: “I had this once on a XG-1, and it was as a result of the mirror slap jarring the circuitry under the shutter release. I had a friend clean the circuits and it worked a treat after that.” No more details there, but a poor electrical contact sounds promising.

There’s a 238-page service manual available for these cameras (thank you Benoît Suaudeau) and it has an electrical troubleshooting section starting at page 174 that says:

Annotation 2019-07-04 204232“AUTO… curtain is kept open” looks like our problem, and “ASA contact defective” seems worth checking. ASA refers to the film-speed selection switch, which is on the top of the camera. It makes sense that a lost contact from that switch would only affect Auto mode, since Auto needs to know the film speed to decide how long to leave the shutter open.

There’s a YouTube video here, by Florian Buschmann, which shows how to take the lid off. The top cover has three axes poking out of it, one for the rewind knob and power switch, one for the shutter button and film speed knob, and one for the winding lever. The components attached to the tops of these can all be unscrewed from their axes and removed, leaving a plastic top-plate attached via four small screws, two at front and two at the back towards the middle of the camera. Here’s the camera with the top off:

Minolta XG-9 with top plate removed

The film-speed switch is beneath the large black nubbin poking out of the top about 3/4 of the way across from the left. The smaller nubbin at the left side is the power switch mechanism and rewind axis, which is the part I was just about to break while reassembling the camera.OLYMPUS DIGITAL CAMERA

Unscrewing the parts atop the film-speed switch reveals a brush mechanism with a flat contact plate. I cleaned the plate with switch cleaner (it was quite grubby) and made sure the brushes were sticking out enough on the switch side, then reassembled the top of the camera.

After reassembly I tested the shutter in Auto mode a few times, and it didn’t stick. Flushed with success, I set out to load a film — and that’s when the power switch came loose. While screwing on the metal collar that keeps the power switch in place, I had managed to shear off the entire threaded top of the plastic part that holds it down. A problem.

The broken part

Minolta part 2006-3309-2, Rewinding axis receiverThe picture on the right shows the part I had broken. It’s intact in this photo, because this was taken during one of my initial attempts to glue it back together again — which always failed when force was applied to screw the threaded collar back on the top.

The 40-year-old plastic is quite brittle, and as you can see, I also broke one of its little lugs just unscrewing it from the body. And I am a reasonably delicate person.

Without this part, it’s impossible to use the power switch: it is left floating, switching between on, off, and self-timer modes at random. Having failed to glue it, my options seemed to be:

  1. Write off the camera. I wasn’t going to do that yet.
  2. Figure out some ingenious bodge to keep using the power switch even though the official mechanism didn’t work. Well, I did sort of do this using a piece of thread attached to the switch mechanism, but I didn’t like that very much.
  3. Find a replacement part. For an easily-broken part in a relatively inexpensive 40-year-old camera from a company that stopped making cameras over a decade ago, that seemed unlikely, and my first searches came up with nothing.
  4. Buy a non-working camera, sold for parts, and plunder it for this part. Yes, but what if it just broke in the same way again? That would be unbearable. Or if this part was already broken in the other camera?
  5. Make a new part. This takes time and money and might not work, but it puts the outcome in my own hands and hopefully teaches me something new.

My first assumption, knowing very little about 3D printing, was that this component was too fiddly to be produced that way — especially the rather fine threaded bit at the top. But reading about different 3D processes, it seemed faintly possible that a nylon SLS printer, with 0.1mm resolution, might just be able to produce a viable part, especially as the thread was required to screw into a metal collar (which could perhaps do a bit of self-tapping) rather than a plastic one.

Modelling the part

Here’s this component in the service manual, identified as “Rewinding axis receiver”. It comes in two variations with codes 2006-3309-02 and 2006-3309-04. I think mine is a 2006-3309-02.Part in maintenance manual

First I needed a 3D model.

I measured it with a vernier caliper and some close-up photos. The thread seems to be 0.5mm x 7mm and the three screw-fixing lugs are spaced at 0°, 140°, and 220°. A hole through the middle admits a metal axle of 4mm diameter. There is a cutout in the collar at the bottom, into which the mechanism to release the film door when the axle is lifted fits. There’s also a slot in the midriff which a metal clip pokes into, to meet a notch in the axle that snaps it into its usual lowered position.

Knowing nothing about 3D modelling software, I asked my kids for advice first. Their suggestion was Blender, but I’m a bit afraid of Blender. I did try Wings3D, another free application (written in Erlang using wxWidgets — interesting!) but I got stuck on how to model a screw thread, and decided I should probably start with a trial version of something expensive with extensive documentation.

I came across Autodesk’s Fusion 360 while searching for screw thread tutorials, when I found a page that basically just said “use the thread tool”, which seemed about right. Fusion 360 is a very expensive subscription product with cloud-storage lock-in, but it has a one-year trial period for “hobbyist” use. That’s me!

Annotation 2019-07-05 203934.png

I really enjoyed using Fusion 360, and I waxed lyrical about it here on Twitter. Much the appeal has to do with good interactive feedback, but the core thing is that it’s built on a very nice 2D sketching program: the expectation seems to be that you sketch in 2D and then extrude into 3D, which I find a lot simpler than trying to design in 3D. But I don’t know how other software of this kind works. Anyway, I successfully built a nice-looking model, though with a thread that I suspected wasn’t really possible to print.

3D printing

I exported the model as an STL file and sent it for nylon/polyamide SLS printing at i.materialise. I have to admit that I picked this company because they had the most anonymous, automatic-looking order page, and I felt embarrassed about having a real person look over my impossible design. I didn’t notice at first that i.materialise are actually in Belgium, and it’s slightly crazy to send your model from London to Belgium for printing when there are companies in London (digits2widgets, 3DPRINTUK) doing the same thing, but by that point I was sort-of committed.

Because of the minimum order price, I ordered three different pieces. Two were from my best attempt at the model, which I asked for once in SLS (laser) process and once in MJF (HP’s ink-based) process. The third was an SLS print with slightly different dimensions for some things I wasn’t sure of. The pieces took about a week to arrive, and the price was quite high — the nominal charge for printing each item was £11.15, but that was quoted before VAT and shipping, and the eventual total was very close to £50.

Here are the results. The black part on the left is the broken original, the white one is the SLS of the variant model, and the grey one on the right is the MJF. (The colour doesn’t matter, as the part is not visible from outside the camera.)

3D printed Minolta parts

Receiving these was a really exciting moment: a true marvel that it was actually possible to design and build this neat little component with no worthwhile expertise on my part!

Of the two processes, the MJF version came out a bit fatter than the SLS — the holes are smaller, the walls are thicker. I think the SLS copy is more true to the design size. Although the texture of the printed nylon is unpolished (they both feel a bit like paper) and looks almost crumbly, both of them feel very solid, are harder and less flexible than I expected, and seem pretty tough.

The threads are indeed pretty sketchy. The SLS one is a little too narrow, without enough depth to the thread: the collar doesn’t tighten well and can easily jump a thread if pushed. The MJF has even less visible thread, but it is a bit too fat, and it is hard to fit the collar onto it at all. In this situation that would probably be a good thing, but the thicker walls of the MJF part interfered with the film-door release disc underneath the part, so it was an SLS copy that I ended up fitting. Here it is in the camera.

3D printed Minolta part fitted in XG-9 camera

I think that the thread, although weak, may hold well enough. It isn’t the last line of defence against the power switch falling off: the rewind knob on top of it, held on with a metal-on-metal screw fitting, is there to prevent that. This thread just needs to stop the power switch from lifting and losing its position while loading or rewinding film. But it would be nice to have done better, if it were possible to do so. I’d like to know if there is some technique for making threads more “printable” at this kind of scale.

Conclusion

This feels like a successful outcome, and at least the original problem is fixed. It would obviously be better not to have broken this part at all — and although it was my fault, I did spend some time mentally railing at Minolta for using a plastic thread here in the first place. Perhaps the main lesson is just that old plastic is fragile. But I enjoyed the process and am happy with the result, which is after all a camera that works better than it previously did.

I’ve published the 3D model, in a Github repository at cannam/minolta-2006-3309-2, in case it is of use to anyone else. If you’ve any suggestions for how this could have been done better, I’d like to hear! Of course this does show a big limitation of using Fusion 360 to do the modelling: the main file in that repo is in a proprietary format and probably useless to any other tool. I’ve included a couple of exports as well, including the STL file.

 

A film camera

I take a lot of photos and I share some of them online via the antique medium of Flickr. Not many people look at them, which I don’t mind, because I imagine my audience to be (a) family and (b) myself, later. Photos I take with people in them are usually visible only to my friends and family. I’m a person who takes photographs, not a photographer.

But I do take some joy in the practice of photography. That’s partly because I can: at my level, there is very little to it: somebody else has done all the hard work. There is massive, long-term, highly technically sophisticated labour behind every functional detail of image capture and reproduction, which all culminates, for routine takers-of-photos like me, in pressing a button or tapping the screen and deciding whether you like the resulting image or not. It’s a ritual that has delivered a spurious feeling of creativity to people for decades, prefiguring the internet age.

There are four categories of potential joy in a photo, and they go in this order:

  1. Looking at whatever it is you’re thinking of taking a photo of
  2. Solving technical problems, or just fiddling with the camera
  3. Enjoying the picture itself
  4. Finding the pic again later and reminiscing

Obviously, photos of your friends in the pub can skip categories 1 (except in a social sense) and 2. Very deliberate landscape photos might have a lot of categories 1, 2, and 3 but not a great deal of category 4. Please understand that I am vaguely blathering about this category thing because it seemed to make sense while I was typing this, not because I think it’s any kind of real system.

I started out taking photos on film, then moved to a digital camera in 2003. By then a digital camera already gave you more pleasure in the likely quality and serendipity of your pictures, good for categories 3 and 4 above. I did keep a film SLR — a Zenit EM, the cheapest second-hand SLR available when I bought it in 1991 — but it’s very clumsy to use, and the category-2 joy you would imagine getting from it never really materialised.

In search of that sort of joy, I recently bought a slightly fancier second-hand film camera from someone on eBay. I wanted something still mostly manual, but more like the kind of thing I never had access to when young. I decided to buy a Minolta, and I’m not ashamed to say that was mostly because I like the old Minolta logo, before they introduced the more familiar Saul Bass-designed all-caps logotype in 1981. The older logo is verging on Comic Sans in its friendliness, and gives the camera a sweet face:

Minolta XG-9

This manual-focus, manual-aperture, automatic exposure Minolta XG-9 dates from about 1980. It was the cheaper of Minolta’s two SLR ranges at the time; the body probably cost slightly more than a 48K ZX Spectrum home computer. It would have been a nice and very practical camera. It also embodies a mind-boggling amount of mechanical complexity compared with modern equipment. To the right is a schematic of the winder mechanism, one of dozens of such illustrations found in the service manual. Winder schematic for XG-9

It was sold to me with a lens at least a decade older than the camera, a splendid-looking chunk of metal with an impressive (and apparently rather 1960s) wide front glass element.

Anyway, I bought this for my category 2, the fiddling. But so far what I’ve appreciated most is the thing I gave as category 1: just looking at the real scene more closely. Without a screen to review photos on, you have to assume that your photo will fail and you will never get to see this again. If an image should appear again, days later when you get the film processed, it’s a fresh delight.

The downside is that the economics of successful photos still apply. That is, only one in ten shots is any good. With a smartphone or digital camera you can take a hundred photos and have ten you really like. With film you buy a 36-photo roll, get three or four decent photos, but have to visit the print shop twice and spend at least £15 buying and developing the film. (Though I was surprised to find that you can still get film processed at Snappy Snaps.)

And how are the photos? Well, it’s a bit like listening to vinyl records. It’s nice for things that benefit from a bit of roughness and vigour, like this kind of thing:

Westbourne Terrace

(That one wanted a lens hood to prevent the flares in the middle and right, but I didn’t have one at the time.)

Or for snaps of people:

41329457102_3b09963088_c

I like both of those a lot, but I’ve yet to get any really successful landscape or “still-life” pics from it and I suspect I never will, now that I’m used to a cleaner, higher resolution digital image.

Will I be using it much? Am I going to carry it around everywhere, but take far fewer and more selective photos than I otherwise might? Probably not, but it might not be up to me anyway. These are fairly solid cameras, but this one is nearly 40 years old and has a few electronic bits as well as sensitive mechanical parts. They do fail in various ways and I don’t entirely trust that it’s going to be still working the next time I want to use it. That primitive but sturdy Zenit will probably have the last laugh.