That's (Not) The Way To Do It!

[Stuart Budd]

Late night poking around in your projector isn't the best of ideas.

Thought I'd see wht the lamp on my SC 18 is too lazy to go out once on. Took back off, had a nosy. I know, I'll clean the mirrors. Take two screws out and they'll slide out! Nope! They're a kind of trapezoid shape and as I was sliding the first out, it wedged!!! I could here little pieces of glass splintering off.

As soon as I have some table space, I end up pulling something to bits!

But whilst I'm here, I may as well replace that perished foam sponge. It's just out of shot. Give it a clean and put back together. Think the issue with the lamp is around the front!

[Steve Klare]

Hey Stuart!

Something like this I usually have an early lunch on Saturday and resolve to work until dinner time if I have to. In extreme cases, my wife and son have left the house! (-sometimes it's a projector, sometimes it's a car, once it was installing a new faucet in the tub!)

-before I start I make sure there's a cold beer in the 'fridge, but strictly reserved for afterwards! (-motivation!)

If the SC-18 is anything like an Elmo ST, there are snap switches which are operated by cams on the control knob shaft. Two turn the motor on and off and change its direction and one turns the lamp on and off. One of these stuck on one of my machines so that when I turned off the transport (-and therefore the FAN!) the lamp stayed lit.

Replacing one of these is fairy serious surgery: maybe TWO beers!

The switches aren't hard to find, but they are mounted in this very complex stack of brackets, insulators and switches that is held to the chassis by three long screws. The right way to put this back together after you solder in the new switches is pile everything on the screws and installing it as a unit.

-trying to pile up everything and THEN install the screws is enough to send you to the beer early!

[Stuart Budd]

Nice one Steve. I'll set to it and report back.

[Steve Klare]

I only replaced one of the three switches: I kind of regret wasting the the opportunity, and will really regret it if either of the two motor switches ever goes.

-although it's been at least ten years.

The switch that controls the lamp takes a real beating because the lamp takes a huge surge of current when it turns on from cold, plus the normal operating current of the lamp is much higher than the motor anyway. After a while the contacts start to burn up and oxidize and when the current is passing through just the last tiny remainder that's still conductive, it gets so hot the two contacts weld together. It's not a great weld: often it breaks and the switch can open, but while it is stuck the lamp stays on.

[Stuart Budd]

Sounds like a job for a relay arrangment. Your tips have paid dividends though. Front control housing off. Neat idea fir the flap hinge. Did a contact spray on lamp switch but not really woking. Untrused. Still in bits at the min will search switches or take apart.

Mirror assembly clean and back together. Glass shards found, one in my finger the other less painfully. Nasty but no damage to mirror itself. Foam sponge replaced too.


Back together.


Switch after work.

[Stuart Budd]

Well. A video is so much easier than trying to explain a complex situation in words. However, a sticky switch pretty much sums this particular situation quite well.

With Steve mentioning heat and lamp amps ( reminds me of cold halogen reflectors for projectors ). It looks like materials have degraded around the switch, making it stick. Each switch, 3 of, is separated with a sort of matting, heat shield, perhaps! I don't fancy shelling out £3 on a few new switches when surgical spirit might do almost as well.
I may even wish I had replaced all 3 in the not too distant future, a lá Steve!
Anyhoo, for your entermatainment 🎦😄

Edit. I've gone the soak it for a bit route!

[Stuart Budd]

Back together bar the front.

Surgical spirit done it's job. Don't know how long this will last.


Dried off and a quick squirt of contact cleaner. Negative of all this is the writing on the switches were wiped clean off!

Should have made better notes of washer placements and connection arrangements. Seems to function but don't have a cable or any film to test. Sold as seen 😋

[Steve Klare]

Hi Stuart,

It looks like changing your switches would be easier than what I am used to: at least you know if cleaning them doesn't work in the long term, plan "B" isn't too bad.

The switches work like this:

The one switch for the lamp is simple: when the lamp is supposed to be on, the cam presses the lever down and the switch closes. The opposite is true when the lamp is supposed to be off.

There are two switches for the motor. Each one chooses (+) or (-) of the motor power supply and connects one (-not both!) of these to one terminal of the motor. The cams are arranged so that one, or the other or neither switch is depressed. One or the other switch being depressed puts (+) on one or the other motor terminal with negative on the remaining one and gives you Forward or Reverse operation. Neither depressed gives you negative on both, so now there is no motor voltage and it stops.

That other cam with the linkage is probably opening and closing the presser on the soundhead to allow for threading and then sound projection.

(This is how the World got by before Firmware!)

The material in-between is electrical insulation to prevent the wiring from shorting to chassis or each other. As long as each has a layer on both sides, you are OK.

(You may have that beer now!)

[Brian Fretwell]

This makes me wonder if the lamp pre-heat on projector was also to lower the current when turning to full power as the resistance of the lamp would already be increased.

[Steve Klare]

Hi Brian,

Yes, that's the idea. The theory is that the shock of that burst of current is damaging to the filament and if you reduce it, the lamps will last longer. After all: think about 10 times when you've blown a lamp, and odds are most will be half a second after you light it.

-as a practitioner of two machine shows, I'm not pre-heat's biggest fan!
.

-I'd rather change the lamp a little more often than keep forgetting to turn the inching knob before I start the other machine.

[Stuart Budd]

Projector Quiz 😊

Right is an Elmo ST-800 !
Left. Eumig.... Super 8 only.... 810 !

Fingers crossed...

[Steve Klare]

Right On for Right! (Was it the 800 foot reel that tipped it off?)
Close for Left: Bolex SP-80 Special...The Eumig 800 Series on undercover assignment. (-an Austrian pretending to be Swiss!)

The Bolex was my first sound machine.
The chassis of this ST-800 was my second, but I rebuilt it with like-new guts about 10 years ago.