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He who forgets the lessons of projector maintenance is condemned to learn them again! (-and AGAIN!)
I go through this every couple of years: changing the belts on an ELMO ST series projector. I have three in active duty: two ST-800Ms and an ST-1200HD M. The thing is with all of day-to-day life that goes on, I have to re-learn how to do it every time!
We have company coming over soon to see a show, and blowing a lamp or breaking a belt would be pretty-bad showmanship. When you put on a show with 45+ year old machines, you don’t want to explain failures to the audience: you just want things to work! So, on the weekend I had two days with some preventative maintenance: one bulb-change and two full belt-changes on the two ST-800s.
The Saturday belt change went per tradition: I had to fiddle around with the method and get it right (…again). The second machine on Sunday was easy. Why? -because I remembered how to do it! Getting this on record is the reason we are here right now: so I and maybe other people won’t need to blunder through this again (-for like the 10th time!). The pictures shown here are from day 2.
Other ideas are of course welcomed. There are probably more approaches possible than mine and as you read, you’ll notice mine is still evolving and doesn’t pretend to be perfect anyway.
I’m sticking with just the long belt this time, because I know this is common to the ST-800 and the ST-1200, and maybe other ELMO STs too. The motor belts are different among ST-800 and ST-1200, so we will save that change for another day.
What I'm trying to do here is show some handy shortcuts that will make the job go more smoothly. It's kind of like having a notebook but making it public.
This belt transmits torque to the take-up reel. It is activated when a gear on a pivot rotates towards the back of the machine under forward film transport motion and engages the gear that’s part of what we will call the front pulley. The belt takes the torque from the front pulley and transmits it back to the rear pulley which is geared to the rear arm drive and then the rear spindle and take-up reel. The rear arm drive contains a one-way drive so the take-up reel can freewheel under rewind.
When this belt breaks the going can get nasty. Since it powers the take-up, when it pops the show will continue-on just as it should, other than anything up to a quarter-mile of film spilling out the back onto the table, onto the floor, down where cats nibble and carpet dust and pet hair are waiting! A couple of hundred feet of film in the wild is just a mind-boggling sight, and definitely something to be avoided!
This is almost an ad. for staying back with the machines, but I’ll have to admit there are days when that couch up towards the screen just calls for me! I need to do what I can to keep my machines trustworthy. (-and every so often I glance back and make sure that reel isn’t stopped! Trust, yet Verify!)
-and I also try to change that belt before it fails. Belts are cheap but cat-chewed prints are just heart-breaking!
.
Picture 1: It was a belt once!
Of course, these belts (and many others like them) are kind of notorious for failing even if you don’t use the machines. Over the course of years the rubber softens into a tarry goo and falls apart. It is revolting stuff, hard to clean off hands and actually ruined my wife's tablecloth! If you buy a machine that’s been in storage for a while, you are liable to find your belts in exactly this condition. The machine we are looking at here was in a camera shop until about seven years ago and this is what the remains of its long belt looked like when I first opened it up. What can you say? They are cheap, simple and quiet: nothing's perfect!
.
Picture 2: Everything still assembled and there's that one Phillips-head screw you need to get started.
Our first obstacle is the fact that installed machinery makes it literally impossible to get the belt off, so we need to clear some of it out of the way. There is a sheet metal fork that leans on the parts mounted to the rear arm. It and the bracket that holds the rear arm in place are secured by a Phillips-head screw. You can loosen this screw and rotate the fork out of the way. Up until now, I have been taking this screw out entirely, but after this time I’m thinking unless there is a need to remove the rear arm it can just be loosened and re-tightened later to keep things simpler. (I’m showing it here as if I just loosened and rotated.)
.
Picture 3: Loosen the Allen Head screws on the One-Way Wheel.
The one-way wheel is mounted with two Allen-head grub-screws. When they are loosened, it slides off the shaft.
.
The rear arm drive-gear underneath the one-way wheel slides freely on the shaft and can be slid-off. Once the gear is off the shaft, the rear pulley is now unobstructed for changing the belt.
,
In some cases (this weekend I had one of each), the stops for the front gear pivot obstruct the belt being removed and replaced. If so, remove the top rear bracket screw, loosen the other and rotate the pulley assembly downwards.
The belts can now be changed. Please remember your hands have been handling greasy parts and you really should wash them before you handle the new belts for best grip and maybe better durability too. Cleaning up the pully sheaves seems like a good idea too if you see gear-grease in them.
I try to make the corner of the belt that nests in the front sheave be the same corner that rests in the rear: this saves a little bit of extra flexure each time around and can’t hurt where longevity of the belt goes.
With the new belt in place, rotate the front pulley bracket into position, replace the removed screw and tighten it, and then re-tighten the other one.
.
Picture 6: Rear arm drive gear re-installed.
The work at the rear pulley is a little more complicated. You replace the rear arm if you dismounted it (-won’t do this next time) and slide that gear down the rear-arm drive shaft with the flatter side facing out from the machine. The side with the extended hub should be facing the machine chassis.
Now replace the one-way wheel. I mount mine with the end of the rear arm shaft flush to the outer edge of this part. Then tighten the two grub-screws. (See picture 3)
That sheet metal fork is there to provide a little bit of drag by leaning on the gear and one-way wheel. The one-way wheel pushes the gear backwards when the belt is stopped but the take-up is spinning, but the gear “walks” up the slope of the beveled gears until it engages the one way when the belt is moving.
I lean the fork on the gear to help the gear slide up the shaft, and I can lean it on the one-way too to increase film tension during rewind if needed. (See picture 2) (I see in the pictures below that the fork is not touching the one way wheel: I may need to fine-tune this later.)
So we’re back together now, and need to test it before we call it a day. The thing is to do this, we need to operate the machine with the cover off. There are Hazardous Voltages in there: TOUCH NO PART of the machine you couldn’t access if the cover was mounted, and you’ll be fine! If you don’t feel knowledgeable and confident, don’t do it! If you do need to make an adjustment, unplug the machine and let it sit for maybe 30 seconds.
.
Picture 7: Transport is in “Forward”. The sliding gear is forced
outwards to engage the one one-way wheel and spin the take-up reel.
(Great action-shot!)
So: we put it in “forward”: the gear should slide outward and the take up reel should spin.
.
Picture 8: The transport is stopped, and the wedge-shaped projections
on the gear and one way wheel force the gear and wheel apart.
Then, we rotate the control knob to “stop” and the one-way wheel should force the gear backwards and disengage the take-up arm shaft from the belt. If the reel keeps spinning and the belt stops, you are OK here. (-no harm trying it a few times for comfort.)
If the reel is dragging the belt along, that's a bad thing: particularly with the ST-800, it doesn't take a whole lot of extra film tension to slip the front spindle clutch under rewind and dragging the long belt and pulleys might be the straw that breaks this particular camel's back. If this happens you may not get all the way to rewinding 800 feet before you have to give it a push!
So now we are done! Theoretically, we have improved the reliability of the machine. Most probably we did, but in the real world we’ve actually just added a couple of unknowns and shouldn’t trust it entirely. (Don’t voluntarily take a long trip with a car that was with the Mechanic that same day…) Maybe a new belt or lamp is defective, maybe you (-or I) made a mistake: we’re all human! For example, on the Saturday machine I found the loading chute would not lock down: while I worked, I’d accidentally disconnected the linkage that latched it. It was a quick fix, but nothing I wanted to do with people waiting in the seats! So, before these people show up, I will be testing these machines with a couple of reels each. (May all your surprises be pleasant ones!)
I go through this every couple of years: changing the belts on an ELMO ST series projector. I have three in active duty: two ST-800Ms and an ST-1200HD M. The thing is with all of day-to-day life that goes on, I have to re-learn how to do it every time!
We have company coming over soon to see a show, and blowing a lamp or breaking a belt would be pretty-bad showmanship. When you put on a show with 45+ year old machines, you don’t want to explain failures to the audience: you just want things to work! So, on the weekend I had two days with some preventative maintenance: one bulb-change and two full belt-changes on the two ST-800s.
The Saturday belt change went per tradition: I had to fiddle around with the method and get it right (…again). The second machine on Sunday was easy. Why? -because I remembered how to do it! Getting this on record is the reason we are here right now: so I and maybe other people won’t need to blunder through this again (-for like the 10th time!). The pictures shown here are from day 2.
Other ideas are of course welcomed. There are probably more approaches possible than mine and as you read, you’ll notice mine is still evolving and doesn’t pretend to be perfect anyway.
I’m sticking with just the long belt this time, because I know this is common to the ST-800 and the ST-1200, and maybe other ELMO STs too. The motor belts are different among ST-800 and ST-1200, so we will save that change for another day.
What I'm trying to do here is show some handy shortcuts that will make the job go more smoothly. It's kind of like having a notebook but making it public.
This belt transmits torque to the take-up reel. It is activated when a gear on a pivot rotates towards the back of the machine under forward film transport motion and engages the gear that’s part of what we will call the front pulley. The belt takes the torque from the front pulley and transmits it back to the rear pulley which is geared to the rear arm drive and then the rear spindle and take-up reel. The rear arm drive contains a one-way drive so the take-up reel can freewheel under rewind.
When this belt breaks the going can get nasty. Since it powers the take-up, when it pops the show will continue-on just as it should, other than anything up to a quarter-mile of film spilling out the back onto the table, onto the floor, down where cats nibble and carpet dust and pet hair are waiting! A couple of hundred feet of film in the wild is just a mind-boggling sight, and definitely something to be avoided!
This is almost an ad. for staying back with the machines, but I’ll have to admit there are days when that couch up towards the screen just calls for me! I need to do what I can to keep my machines trustworthy. (-and every so often I glance back and make sure that reel isn’t stopped! Trust, yet Verify!)
-and I also try to change that belt before it fails. Belts are cheap but cat-chewed prints are just heart-breaking!
.
Picture 1: It was a belt once!
Of course, these belts (and many others like them) are kind of notorious for failing even if you don’t use the machines. Over the course of years the rubber softens into a tarry goo and falls apart. It is revolting stuff, hard to clean off hands and actually ruined my wife's tablecloth! If you buy a machine that’s been in storage for a while, you are liable to find your belts in exactly this condition. The machine we are looking at here was in a camera shop until about seven years ago and this is what the remains of its long belt looked like when I first opened it up. What can you say? They are cheap, simple and quiet: nothing's perfect!
.
Picture 2: Everything still assembled and there's that one Phillips-head screw you need to get started.
Our first obstacle is the fact that installed machinery makes it literally impossible to get the belt off, so we need to clear some of it out of the way. There is a sheet metal fork that leans on the parts mounted to the rear arm. It and the bracket that holds the rear arm in place are secured by a Phillips-head screw. You can loosen this screw and rotate the fork out of the way. Up until now, I have been taking this screw out entirely, but after this time I’m thinking unless there is a need to remove the rear arm it can just be loosened and re-tightened later to keep things simpler. (I’m showing it here as if I just loosened and rotated.)
.
Picture 3: Loosen the Allen Head screws on the One-Way Wheel.
The one-way wheel is mounted with two Allen-head grub-screws. When they are loosened, it slides off the shaft.
.
Picture 4: The gear is off: ready to dismount the belt from the rear pulley.
The rear arm drive-gear underneath the one-way wheel slides freely on the shaft and can be slid-off. Once the gear is off the shaft, the rear pulley is now unobstructed for changing the belt.
,
Picture 5: front pulley: one screw loosened, one removed so its bracket can be rotated downward and the belt freed for replacement.
In some cases (this weekend I had one of each), the stops for the front gear pivot obstruct the belt being removed and replaced. If so, remove the top rear bracket screw, loosen the other and rotate the pulley assembly downwards.
The belts can now be changed. Please remember your hands have been handling greasy parts and you really should wash them before you handle the new belts for best grip and maybe better durability too. Cleaning up the pully sheaves seems like a good idea too if you see gear-grease in them.
I try to make the corner of the belt that nests in the front sheave be the same corner that rests in the rear: this saves a little bit of extra flexure each time around and can’t hurt where longevity of the belt goes.
With the new belt in place, rotate the front pulley bracket into position, replace the removed screw and tighten it, and then re-tighten the other one.
.
Picture 6: Rear arm drive gear re-installed.
The work at the rear pulley is a little more complicated. You replace the rear arm if you dismounted it (-won’t do this next time) and slide that gear down the rear-arm drive shaft with the flatter side facing out from the machine. The side with the extended hub should be facing the machine chassis.
Now replace the one-way wheel. I mount mine with the end of the rear arm shaft flush to the outer edge of this part. Then tighten the two grub-screws. (See picture 3)
That sheet metal fork is there to provide a little bit of drag by leaning on the gear and one-way wheel. The one-way wheel pushes the gear backwards when the belt is stopped but the take-up is spinning, but the gear “walks” up the slope of the beveled gears until it engages the one way when the belt is moving.
I lean the fork on the gear to help the gear slide up the shaft, and I can lean it on the one-way too to increase film tension during rewind if needed. (See picture 2) (I see in the pictures below that the fork is not touching the one way wheel: I may need to fine-tune this later.)
So we’re back together now, and need to test it before we call it a day. The thing is to do this, we need to operate the machine with the cover off. There are Hazardous Voltages in there: TOUCH NO PART of the machine you couldn’t access if the cover was mounted, and you’ll be fine! If you don’t feel knowledgeable and confident, don’t do it! If you do need to make an adjustment, unplug the machine and let it sit for maybe 30 seconds.
.
Picture 7: Transport is in “Forward”. The sliding gear is forced
outwards to engage the one one-way wheel and spin the take-up reel.
(Great action-shot!)
So: we put it in “forward”: the gear should slide outward and the take up reel should spin.
.
Picture 8: The transport is stopped, and the wedge-shaped projections
on the gear and one way wheel force the gear and wheel apart.
Then, we rotate the control knob to “stop” and the one-way wheel should force the gear backwards and disengage the take-up arm shaft from the belt. If the reel keeps spinning and the belt stops, you are OK here. (-no harm trying it a few times for comfort.)
If the reel is dragging the belt along, that's a bad thing: particularly with the ST-800, it doesn't take a whole lot of extra film tension to slip the front spindle clutch under rewind and dragging the long belt and pulleys might be the straw that breaks this particular camel's back. If this happens you may not get all the way to rewinding 800 feet before you have to give it a push!
So now we are done! Theoretically, we have improved the reliability of the machine. Most probably we did, but in the real world we’ve actually just added a couple of unknowns and shouldn’t trust it entirely. (Don’t voluntarily take a long trip with a car that was with the Mechanic that same day…) Maybe a new belt or lamp is defective, maybe you (-or I) made a mistake: we’re all human! For example, on the Saturday machine I found the loading chute would not lock down: while I worked, I’d accidentally disconnected the linkage that latched it. It was a quick fix, but nothing I wanted to do with people waiting in the seats! So, before these people show up, I will be testing these machines with a couple of reels each. (May all your surprises be pleasant ones!)
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