Better Speed Regulation With An Electronic Speed Controller

As previously mentioned, the Pathé Marignon projector had a rudimentary speed control system provided by a wire-wound potentiometer in series with the motor.

aboveAfter disassembly of the old supplementary chassis, I noted that this potentiometer was marked “V. ALTER FRANCE”, which suggests my father had retained this speed control potentiometer from the original unmodified projector. Sturdily constructed from metal, ceramic and some kind of varnish, this is an example of a component from the pre-plastic era.

In the age of silicon chips, there are better ways to control motor speed and indeed it was in the Australian magazine “Silicon Chip” that a solution was found. Published in May 2009 — just in time for this project — was a “High Performance 230VAC 10A Full-Wave Motor Speed Controller”. The article promised:

“This full-range Motor Speed Controller will give smooth control from near zero to full speed on electric drills, routers, circular saws, lawn edgers, food mixers — in fact any appliances with universal (brush-type) motors.”

Not surprisingly they didn’t mention ancient 9.5mm film projectors! But the Pathé Marignon did have a universal (brushed) motor, so this controller seemed a good match.

Unlike conventional phase-control devices which use an SCR or Triac to delay the switch-on point during each half cycle of the 50Hz AC waveform, this new design uses a more sophisticated high frequency (1.25kHz) pulse-width-modulation (PWM) system. The motor current is switched using a high power Insulated Gate Bipolar Transistor (IGBT). To quote further from the article:

“There are 12 pulses during each half-cycle, so the motor receives a more continuous stream of current compared to when driven via phase control. As a result, the motor operates very smoothly over the whole of its speed range.

“For speed regulation, the circuit does not rely upon back-EMF from the motor. Instead, it monitors the current through the motor and adjusts the pulse width to maintain the motor speed. If the current rises, indicating that the motor is under load, then the pulse width is widened to maintain motor speed.”

I anticipated that this new hi-tech speed controller would achieve much better speed regulation than the primitive potentiometer method. So I ordered the kit from Jaycar Electronics and, with soldering iron in hand, commenced construction.

One minor issue was that this electronic speed controller was designed to operate on 230VAC, whereas the French-designed Pathé Marignon operated on 110VAC via an external step-down transformer. I contacted Silicon Chip Magazine and they advised that the circuit should work just as well at 110V if one resistor was replaced with a wire link, which was done.

The speed controller printed circuit board (PCB) was designed to fit inside a cast aluminium box which doubled as a heatsink for the power transistor (IGBT) and the bridge rectifier. It made sense therefore to construct the controller in this box as designed, and then mount the entire box inside the new projector base.

aboveCloseup of the new electronic speed controller PCB mounted inside the cast aluminium box. The power transistor which switches the motor current is visible at the top of the photo (also a power diode), mounted onto the aluminium box which serves as a heatsink. A bridge rectifier which supplies DC for the electronics is visible at bottom left. The wire with the red plastic sleeve exiting through the hole on the left leads to the motor.

Building a kit like this is not difficult. It just takes care and patience, the right tools and checking and double-checking that no mistakes have been made. Once the PCB was complete and checked, it was mounted into the aluminium box and then fitted inside the new projector base.

The power inlet socket, new switches for lamp and motor and a new speed control potentiometer (which connects to the electronics, not directly to the motor) were then fitted into the pre-milled holes in the new steel base.

It was then just a matter of running the required wiring to join everything up. The lamp and lamp-house runs very hot, so normal plastic-insulated wire would not be suitable. Fortunately I had found in my father’s “wire collection” some high temperature insulated wire originally purchased in the 1960s. The insulation may have been made of the now dreaded asbestos, but it was in good condition and posed no danger and turned out to be perfect for the lamp wiring.

aboveThe new speed controller inside the projector base with wiring all in place. At left is the yellow high temperature wire for the lamp.

aboveThe rear panel of the new projector base, showing the controls. Switches for motor and lamp at left and speed control know on the right. Simple and sufficient.

Having carefully completed all the wiring and testing it with a digital multimeter, it was now time to run a live test on the new controller connected to the cleaned and reassembled projector motor.

Fingers crossed, I plugged the unit into the 110v transformer, switched it on and voila!, it worked perfectly, with excellent control of motor speed, even down to very low speeds.

aboveThe power inlet socket is a standard IEC type but in this application it must NOT be connected to 230VAC. This would quickly burn out the projector motor. It has to be run from 110V only.

The next post will cover re-assembly of the projector mechanism.

A New Base Chassis For New Electronics

With restoration and painting work on the upper chassis coming along well, it was time to look at the metal box on which this upper chassis had been mounted.

The original Pathé Marignon projector had a shallow steel base with folded edges, about 18mm high. This defined the overall footprint of the projector and acted as a base for the upper chassis. It also housed rubber feet to prevent the projector scratching any surface on which it was placed.

above The original shallow base made of folded steel sheet. This had been drilled, cut and variously mangled over the years and the paintwork, like that on most of the machine, was badly stained with oil.

My father had added another steel box underneath this original one. In fact it was an old radio or amplifier chassis, obvious from the valve (tube) socket holes which had been patched over with a sheet of aluminium. The entire box had been painted with grey crackle-finish paint, now well past its use-by date.

The purpose of this supplementary chassis base was to accommodate circuitry for optical sound. The 110volt AC input had been re-routed into this new base which sported a series of switches added by my father.

above A view inside of the supplementary base showing the controls on the front-side of the box.

My father had done considerable work on this machine over the years. He had added optical sound to what was originally a silent projector. At one time he even added magnetic stripe playback (and perhaps even recording) facilities, which had subsequently been removed. All these changes had left a trail of holes drilled and then patched over.

There were switches for motor, lamp, exciter lamp and audio pre-amplifier (which was built into the base). See the following photo.

above A closeup of some of the controls on the supplementary chassis added by Denzil Howson. The motor, projection lamp, exciter lamp and audio amplifier each have their own toggle switches. The left hand knob controls motor speed via a wire-wound potentiometer. The right hand knob is output volume from the amplifier.

The supplementary chassis had originally been fitted with a valve pre-amplifier connected to a photo-electric cell. By the early 1980s, either the pre-amp or the photocell were malfunctioning. Having graduated from electrical engineering only a few years before, I designed and constructed for my father new electronics based around a phototransistor and an integrated op-amp for the pre-amplifier. This new and more compact amplifer was built into a die-cast aluminium box mounted inside the projector base.

Notable also on this modified Pathé Marignon was the motor speed control. This used a series-connected wire-wound potentiometer for speed adjustment together with a couple of fixed value wire-wound resistors to switch between nominal speeds of 16fps and 24fps (frames per second).

Series resistance control of a universal (brushed) motor can be erratic and the motor speed was liable to wander around, requiring regular manual tweaking during projection to maintain close to a constant speed.

Part of my plan in restoring this machine was to replace this series-potentiometer speed control with a solid-state electronic speed control.

above This view underneath the supplementary chassis shows at top left the toggle switches seen on the previous photo. Below that are a couple of wire-wound resistors used in series with the brushed motor to switch motor speed between nominal 16fps and 24fps. At left bottom is a power supply for the amplifier. The large transformer at centre left provides 12VAC for the exciter lamp, above and to the right. The exciter lamp is simply a 12V car headlamp! Below the exciter lamp you can see a cutout through which the flywheel for the sound drum protrudes. Finally at top right is an aluminium box enclosing the “new” (1980s) solid state preamplifier for the optical sound photodetector.

I decided early on that this supplementary chassis and its contents were not worth keeping. It was flimsy, full of holes and un-restorable.

My initial plan was to simply replace this base with a new one of identical dimensions. However the question arose where to place the controls and the electronics for the new motor speed controller.

One option would have been to fit the controls onto the upper cast aluminium chassis. This was where Pathé sited the original controls for the projector as can be seen in the photo below.

above In this photo of a Pathé Marignon for sale on eBay you can see the original position of the controls in the upper chassis below the lens holder.

While the controls could have been mounted there at a pinch, there really wasn’t sufficient room to house the printed circuit board for the new motor speed controller inside the projector housing behind the motor and main drive mechanism.

Hence I decided to replace the original folded steel base with one of identical horizontal dimensions but deep enough to accommodate switches, power inlet socket and speed control knob on the side panels. The interior of the box would be large enough to accommodate the new motor speed controller, itself constructed inside a die-cast project box.

After careful experimentation and measurement, I constructed an accurate cardboard mockup of the new base.

above The new projector base fabricated from cardboard with key dimensions marked. This was provided as a pattern to a local sheet metal fabrication shop who replicated it in sheet steel. Using a fancy water-cutter, they were able to make accurate holes for the power inlet socket and switches.

above The new steel base after it had been drilled and painted with grey hammer-finish to match the upper cast aluminium chassis. I drilled the fixing holes in the top surface after very careful measurement against the tapped holes in the upper chassis.

above The new steel base from below. As you can see, there is plenty of space inside to accommodate new electronics for the motor speed control. A separate steel panel screws onto the bottom to seal the unit.

Having already ordered a kit for the new motor speed controller, it was now time to start putting that together. That’s the subject of the next post.

Painting The Chassis and Other Parts

The projector had originally been painted in a mid-grey crackle finish paint. The main chassis, feed and take-up arms and lens holder all had this finish. However, as explained in earlier posts, the condition of the paintwork was very poor. Over fifty years of weathering plus the effects of ubiquitous lubricating oil had turned the paintwork a dirty grey-green.

After removing this old paint, the metal surfaces were scraped, filed and sanded back to a clean finish in preparation for painting.

I had decided to repaint the machine using a dark grey hammer-finish paint, readily available in a spray can. This spray-on finish can be applied directly to ferrous metal, but application to Aluminium requires an etch primer coat first. This is also available in the convenience of a spray can.

The first task was to spray the outside of the main Aluminium chassis with the etch primer. This was a light grey colour with a very smooth finish. Once that had dried, the finishing coat of hammer-finish could be applied.

above Here you can see the main chassis after spraying with a few coats of the dark grey hammer-finish paint. Note the masked areas which should not receive paint. Also the use of bamboo skewers to plug small holes to keep the paint out. The painted chassis looked very smart indeed.

The interior of the main chassis had originally been painted black. I wanted to re-coat this too, and for that purpose had purchased a spray can of matt black enamel.

above Here you can see the inside of the main cast Aluminium chassis after cleaning but before painting. Masking tape around the outer edges will keep overspray from the newly painted outside surface. I also masked the bearings for the main drive shaft and the claw mechanism to ensure no paint got into them.

above Spraying the black matt paint was straightforward and the extra effort paid off in a uniform and new looking finish. Here you can see the interior of the main chassis after spraying. The masking tape was carefully removed after the paint had dried.

above With the chassis painting completed, various smaller pieces needed preparation and painting. Here is the take up arm after removal of the original paint. When the projector had been modified in the 1950s, a full size take up spool would not clear the larger base which had been fitted. So my father cut the take up arm in half and extended it with a small brass plate and some one-eighth inch bolts and nuts.

Because I was removing this oversize base, the take up arm could be restored to its original length. The metal fabricators who made the new base for the projector (more on that later) were also able to weld the two halves of the take up arm together.

above Here is the welded take up arm sprayed with the dark grey hammer finish. You can see the weld and the filled bolt holes in the middle. Almost as good as a new one!

above The feed reel arm was also stripped and repainted. Here you can see it after painting. The spindles at each end were covered in masking tape, still visible in this photo. All these small pieces required building up a series of light coats of the hammer finish paint, both to prevent paint runs or sagging if too much is applied too quickly, and to achieve coverage from different spray directions so that all nooks and crannies are painted.

above Now it was the turn of the lens holder — a detailed casting perhaps in a zinc alloy, shown here after removal of the old paint. This was a precisely manufactured and put together piece. See the photo below of the lens holder before disassembly under the post “More Disassembly”. I carefully dismantled this piece and put the tiny screws and metal parts into labelled yoghurt containers. Only the spring ball which clips the lens holder firmly into position could not be removed. I opted to cover it in a small piece of carefully cut masking tape.

above How clean and new it looks with a fresh coat of paint. This being a non-ferrous metal, I opted first to use the same etch primer used on the main Aluminium chassis. Once that had dried, multiple coats of the dark grey hammer finish spray paint were then applied.

Cleaning, Stripping and Filling

It has taken about a week, spending one or two hours a day, to disassemble the projector into its component parts. Most of the parts have been stored in small plastic yoghurt containers, carefully labelled.

Now to begin cleaning everything — because every part, large and small, is covered with oil and grime after fifty years. The first challenge is how to remove the paint from the main cast aluminium chassis.

A couple of months back I restored a pair of Pathé 9.5mm film winders and discovered that immersing painted metal parts in boiling water made the paint wrinkle and come loose so it can be easily scraped off with a scraper or screwdriver. The paint has to be kept hot or else it starts to stick again to the metal.

above Here is the cast aluminium chassis with all removable components removed. You can see the poor condition of the paintwork which appears impregnated with oil in places. There is no question of a superficial clean fixing this problem. The paint will need to be painstakingly stripped back to bare metal. Then re-prime the metal and spray with a dark grey hammer finish paint.

above Here is the same chassis after cleaning by immersion in boiling water and manually scraping the paint with a screwdriver. Once most of the paint had been remove that way, it was sanded manually with emery paper. There are still traces of the original black undercoat but the surface is smooth enough for repainting. I’ve begun filling the unneeded holes with two-pack epoxy filler, which then needs to be filed and sanded smooth prior to painting.

above The inside of the cast aluminium chassis after cleaning doesn’t come up too badly, although the paintwork is scratched or discoloured in places. I’ve taken the decision to re-spray these inner surfaces with matt black paint.

above Another view of the aluminium chassis, looking end on. At right you can see the slot where the gate assembly mounts. On the left is the bracket which holds the motor sub-assembly. You can also see the brass or bronze bearings for the main drive shaft (in the centre) and for the axle of the claw mechanism at left. This photo was taken before filling the holes with epoxy filler.

above Preparing the chassis for painting has taken some time. Filling the unneeded holes has required two or three applications of epoxy filler — filing the excess off each time and then filling any small cracks or crevices which are left. The remaining holes and the previously unpainted faces where the reel arms and the sprocket holders go need to be protected during painting. Here you can see masking tape applied to these areas. Small holes have been plugged with bolts or with bamboo skewers with their tapered ends pushed into the holes.

above Here is a close-up of the holes which originally housed the motor and lamp switches and speed-control knob. These controls were removed by my father when he modified the projector in the 1950s and the holes were covered with a metal shim. Here the holes have been filled with epoxy putty and then filed and sanded flat. All is now ready for the painting operation.

More Disassembly

When I started this project, I never realised how many components made up this Pathé Marignon projector.

above As an example, look at the lens holder in this photo. A very intricate assembly built around a precision aluminium casting. The lens itself is threaded and can be push into and out of the holder against a sprung pin which mates into the thread on the lens.

The pressure plate is visible in the foreground and in use is held against the gate by pressure from two small springs, just visible in this photo.

Some of these screws and components are very small and require a jewellers screwdriver to move.

Unfortunately the paintwork on this piece, although in better condition than that on the main chassis, had also been affected by 50 years of oil and grime. It will need repainting, and to do that means completely disassembling it back to the plain aluminium casting, then removing the old paint and re-spraying it with new paint.

A collection of small used yoghurt containers proved invaluable for this project. As each subassembly is taken apart, all the pieces are placed into one or more carefully labelled yoghurt containers.

above Here is a view underneath the projector base, after it has been removed from the metal box which my father had fitted and which housed the controls and electronics for sound-on-film. You can see the large brass flywheel poking through a hold cut into the metal base. The flat brass plate is about 6mm thick and is used as reinforcement for the comparatively thin steel chassis. Onto this brass plate the flywheel bearings were mounted.

None of this will be needed in the refurbished machine, because my plan is to remove the sound capability and restore the projector to its original silent condition.

above Here is the flywheel and its shaft and bearings viewed from above. This entire assembly was added by my father in the 1950s. It’s certainly very solid. Together with the metal box mounted underneath the machine and containing a heavy transformer for the exciter lamp, these additions would have added considerably to the weight of the projector. This entire assembly will be done away with. The flywheel is not needed for a silent projector and the metal base has been drilled and filed so many times that it would be impossible to repair. It will be replaced by a new base.

above You can see the shutter assembly here (on the right). It fits onto the end of the main drive shaft (on the left). The shutter does one full turn for every frame of film that advances. As you can see, the light is interrupted three times in each cycle. During one of those interruptions, the film is quickly pulled down by the claw mechanism

You can see a rounded-triangular cam on the end of the drive shaft. This moves the claw mechanism up and down while at the same time, a ramped ring on the shutter assembly (you can’t see the ramping easily in this photo) pushes the claw forwards when it needs to grip the film. It’s a simple yet ingenious mechanism which works quite reliably.

above Taking things one step further, here is the old metal base with the flywheel assembly removed. This is one for the dump.

above A few steps later, we can see the inside of the aluminium chassis with all but the motor and claw mechanism removed. I am impressed with the quality of engineering and the finish in this machine designed and made in the early 1950s. The chassis however, like almost every part of this machine, is covered in a thin layer of oil. The outside grey crackle-finish paint has changed colour from its original neutral grey (visible in parts newly exposed) to a dirty green-grey. It needs to be completely stripped and repainted.

above A view from the rear gives a clearer look at the claw mechanism visible above the motor. You can see the layers of grease, oil and dust on the unpainted metal surfaces.

above A closeup of the motor and claw mechanism with the rear of the film gate visible at right. The motor is a subassembly which mounts onto the main cast aluminium chassis with four screws and a set of eight rubber washers to isolate the motor vibration from the main chassis. Unfortunately, as can be seen here, these rubber washers have long ago perished, not helped I’m sure by the presence of oil. They will need to be replaced also.

above The lamphouse subassembly is made from folded sheet steel, painted black. At the left you can see the condenser lens which focusses the light onto the film gate. The lamp is 110 volt 250 watts. I’m not sure whether such lamps are still manufactured, but luckily the lamp in the machine still works and my father had the foresight to purchase a stock of spares which may come in useful. Note the brass and porcelain lampholder visible through an opening to which the fan cowl connects, ensuring an updraft of cooling air to prevent the lamp from overheating.

Disassembly Begins

This project began with the desire to show some old 9.5mm films. The narrow film gauge had been used by my father to record family activities during the 1950s and his collection of a few dozen reels of 9.5mm, both colour and black and white came into my keeping a couple of years ago.

Although the Pathé Marignon projector worked when plugged into its 110 volt transformer, it clearly was in a bad state of disrepair.

Superficial cleaning would not be sufficient. There were signs of oil in every nook and cranny. The paintwork had turned from grey to a dirty olive colour. And the myriad modifications over the years had left the chassis pock marked with holes, some of which were covered with makeshift patches of cardboard, plastic or tinplate.

In any case it would be a challenge to take apart the machine, clean every piece thoroughly, patch the chassis, repaint it, and reassemble.

So began the process of disassembly…

above Here we see the upper cast Aluminium chassis removed from the lower chassis which was added by my father and was not part of the original machine. The cast chassis bolts onto a small folded steel base. In this photo you can see how part of that base had been cut away to accommodate the flywheel for the sound drum.

The gears which drive the feed and take-up sprockets have been removed. Each gear fits onto a spindle which feeds through a cast Aluminium “housing” mounted on the film side of the chassis. These “housings” have been removed also and you can see the three holes for the mounting screws, top and bottom.

After removal, I placed each part into a small plastic used yoghurt container and carefully labelled the container with the function of the part. In some cases I also made notes and sketches in a notebook in order to guide the reassembly process later. The order of washers or pieces which fitted onto a shaft is an example of information which would be easily forgotten and the absence of which could make reassembly difficult.

above In this photo of the film side of the chassis, the lens assembly, sprocket housings, feed rollers and reel arms have been removed. It gives you a better look at the dirty and adulterated condition of the chassis. A lot of holes which are no longer needed — in particular those associated with the optical and magnetic sound systems which the projector had sported at various times.

The folded steel base was no longer straight. Repairing this would be impossible. Simpler to just replace it with a new steel base made for the purpose.

above Now a closer look at the area of the chassis which had accommodated the sound machinery. The three holes at the left are part of the original Pathé manufacture. They accommodated switches for motor, lamp and speed control. However they had been disconnected when these functions were moved into the secondary chassis in the 1950s. The old holes had simply been covered by a piece of tinplate painted grey.

The condenser lens assembly for optical sound had protruded through the left hand hole in the folded steel base. The right hand hole had accommodated a socket for a photo-electric cell added in the 1950s and subsequently replaced in the 1980s by a phototransistor pickup.

A Closer Look at the Pathé Marignan Projector

As can be seen from the photos in the previous post, the original Pathé Marignan projector was quite a compact unit. The outer case was made of plywood covered in a kind of grey bookcloth material. Most of the machine's workings are mounted on an L-shaped cast Aluminium chassis. This includes the drive motor, pulleys, shutter and claw mechanisms, and a drive shaft which connects to the feed and take-up sprockets. The cast Al chassis is in turn mounted on a simple folded steel base.

The projector which I am refurbishing had been heavily modified in the 1950s by my father. The most obvious change to the appearance of the machine is the addition of a large folded aluminium box to the base of the machine. On closer inspection, this box turned out to be what was probably an old valve radio or amplifier chassis — there were signs of holes which had once contained valve sockets.

This supplementary chassis was bolted onto the base of the original projector and contained the following items:

• A transformer for supplying 12 volts AC to an exciter lamp for optical sound.
• A condenser lens assembly which focussed the light from the exciter lamp onto the film soundtrack.
• A cutaway to accommodate a large brass flywheel which stabilised the film motion as it went around the sound drum.
• An amplifier for the optical sound signal collected by the photoelectric cell.
• A wire-wound potentiometer for controlling motor speed.
• Switches for the motor, motor speed (16 or 24fps), lamp and amplifier.

Sometime in the 1980s I had designed a new solid state optical sound system for this projector which used a phototransistor in place of the original PE cell and an op-amp for amplifying the signal to line level. This latter version of the optical sound system was the one in place when the projector came into my hands.

The following photos show more detail of the machine prior to starting refurbishment. Click on any photo for a larger version.

(Above) Here is another view of the projector. It has clearly suffered the wear and tear of time and significant modifications done in a rather rough manner.

(Above) The original outer casing has also been modified — hacked into at various stages and then patched up again. The black plate on the rear covers a hole that once contained a moving coil meter. This was probably part of a magnetic sound system which the machine sported at one time. A second motor had been fitted for that purpose — perhaps because of excessive electrical interference generated by the brushed drive motor. The secondary motor sat atop the machine in the area cut away from the rear of the cover (and now filled with a steel grille). The two silver vents are also later additions. The four-pin socket in the rear of the base is the inlet socket for 100v power — actually an old 4-pin valve socket plug, completely obsolete these days.

(Above) A closer look at the film path. The original grey crackle-finish paint work on the chassis had turned brown over the intervening 50 years. A home-made strobe disk mounted on the take up sprocket was used in the past for setting speed — there was once a small neon lamp which swung into position in front of this strobe disk. The neon flashed at 50Hz and could be used to accurately set the machine's speed to 16fps or 24fps. Note the sound drum and auxiliary film feeder at the bottom. The little black device sitting in front of the sound drum holds the phototransistor for reading the soundtrack from the film. A piece of black cardboard covers holes in the base which originally accommodated a photoelectric cell, part of the 1950s optical sound additions. The exciter lamp and condenser lens are mounted in the large base unit and focus a slit of light upwards onto the optical film soundtrack. For the purposes of refurbishment, I intended to remove the optical sound system since preserving it would be too difficult and all of the home-made 9.5mm films in the collection are silent.

(Above) By the time so many modifications had been made to the projector in the 1950s and later, the control panel was somewhat of a mess as you can see.

(Above) Underneath the machine we see the contents of the aluminium chassis added by my father in the 1950s. It was added to support optical sound. You can see the 12v car headlamp used as an exciter lamp. The transformer supplies 12v for the exciter lamp. The power supply at lower left supplies abut 12v DC for the solid-state preamp which is in the diecast box at top right. You can see the flywheel for the sound drum poking through at lower right. The wiring was a real rats nest. This entire base will be replaced by a new smaller base with new electronics for motor speed control, new switches and new controls.

(Above) Taking off the outer cover we can see the drive mechanism. Dating from the early 1950s, this French designed and manufactured machine is solidly engineered. The copper tubes at the top were an addition by my father — a lubrication system which had become disconnected. It needs to be removed. The original Pathé design includes a simple lubrication system which we will restore. The mechanism is still in good working order, just very dirty with a 50-year pile up of grease and dirt. It all needs a good clean and a reassemble.

(Above) Finally a close up of the fan and cowl, the latter being added by my father in the 1950s. I don't know what was originally in place of this. From the photos of the Pathé Marignan for sale on eBay, it appears that the case may have contained space for stowing a power cord. Anyway, we will need to keep this cowl for the time being. The belt drive from the motor shaft onto the main drive shaft, on which is mounted the shutter, can be seen in this photo. The drive belt is quite loose. Is it the original one? I don't know. This one looks very much like an O-ring! I suspect a slightly tighter drive belt will be required.