Elmo st800 lamp stays on ?

[Jason Moffatt]

My elmo st 800 has just developed a problem.The lamp stays on all the time, it comes on as soon as it is plugged in before operating the main switch, it still works ok but the lamp just does not go off.Anybody got any ideas what the problem could be ?

[Steve Klare]

Hi Jason.

One of mine had this problem about ten years ago and I fixed it.

There are three lever-operated switches inside the chassis. Two of them select the direction of the transport motor and turn it on and off. The third turns the lamp on and off. The levers are operated by cam lobes on the control knob shaft.

The one for the lamp carries a lot of current including a big surge when starting a cold lamp: the contacts take quite a beating. Over the years the contacts burn so that the current is conducted through a smaller and smaller area, which gets hotter and hotter until that fateful day comes when they get so hot they literally weld together. This is where you are today.

-it's also possible your switch has had some internal mechanical failure, but either way: it's the switch.

It's possible to fix this, even if it's not easy. There is this stack of switches, insulators and spacers that sits on the same side of the chassis as the transformer and flywheel (etc.). You need to disassemble all this, solder in a new switch, and reassemble. I tried stacking all the parts up and fishing the screws through the holes a couple of times, and it was very uncooperative! The best way was load the pieces on the screws and then install the whole mess as an assembly. (Then I had a beer: because I'd earned it!)

Take a lot of photos while you work: it's a lot of pieces fitting together and it's nice if they wind up back where they started.

The switches are still being made and should be easy to find. I saw one like these being sold as a microwave oven part recently. When I repaired mine, I cheated and snipped one out of the motor circuit of a dead machine (less current). I really should have bought three new ones and replaced them all to maximize the benefit of the work I did, but it's been 10 years and it's doing fine.

[Jason Moffatt]

Hi steve, thanks for the reply.Well i have managed to get it working again just by pushing the levers with a screwdriver and spraying switch cleaner over them, i could get to them from the bottom of the projector with the back taken off.So far its ok but if it has done it once it will probably do it again.

[Steve Klare]

Hi Jason,

I remember my lamp sticking on every so often at first, but steadily getting worse. Where it becomes a real problem is it allows the lamp to be powered up without the motor running, so without cooling air. If there happens to be film in the gate, this becomes disaster time! (-depending a lot on the film, I guess!). Beyond that, the lamp is pretty desperate for that nice stream of cool air: I seriously doubt it would last a whole minute without it.

-So if you reach the end of the film and you douse the lamp and it doesn't cooperate, the wrong move is to stop the transport: let the film clear the machine and pull the plug.

I always like to put things like this in some kind of perspective. The people that designed these machines never intended them to be operating in the far off 2020s (-when people dress in aluminum foil, live in houses 500 feet in the sky and vacation on the moons of Saturn!), so we can cut them some slack when they show their finiteness!