Xenon Lamp Adjustment

[Mark Norton]

Replacing the Xenon lamp in my GS1200, and setting the Z axis (or back & forth adjustment.) with the lens out.

The information I have is to make the adjustment on the Z axis untill you see a little bit of plasma around the eye (anode shadow), question is how much? I can focus the lamp from a wide plasma ring to a total black spot.

I imagine this would be the same for most xenon lamp projectors.

[Lee Mannering]

Mark I'll have the Xenon service manual somewhere so will have a look see.

I have returned.
Cant find it in my Service manual so will have to rely on vintage brain cells. Only ever changed a lamp in the GS Xenon once and that was a very long time ago.
From memory
Remove front cover, big green film guide, amp to left as you need clear access to back of lamp.
You will see 3 X Phillips screw heads and these adjust/focus the lamp.
Strike up the lamp and throw a wide picture onto your screen to achieve a even coverage across the frame slowly adjusting the screws.
Reassemble.

[Mark Norton]

Thanks lee, problem sorted now. This might be of interest, what I found on the web (for 35mm Xenon Lamp projectors):

Lamp Alignment Steps


Make the axial (or back & forth) adjustment (the “focus” on the Z axis) til you see a circle with a little bit of plasma around the edges of the anode shadow (people call this “the eye”).

Make your horizontal and vertical adjustments until you get as close to a symmetrical circle as possible.

Re-adjust the axial alignment to bring the plasma back into focus, until you have a tight symmetrical circle free of light (plasma) fluttering around the anode shadow.

After you put the lens back in look for even illumination across the screen. With the lens in, the shadows will be gone and there will be a hotspot in the center of the screen. Focus the lamp (making fine X and Y axis adjustments as necessary) until no shadows are visible at the corners and the illumination is even across the screen.

You may want to fine-tune the lamp focus with the lens in place until you have even illumination, then take the lens out again to check the symmetry of the anode shadow.


I followed the above, but in practice, ( with the lens out) I found a "Bright White Halo" around the anode shadow visible.

Using the brass adjuster on top of the lamp, I brought the Z axis ( Back & forth) adjustment to get the "Halo" in to the brightest possible luminance & focus. (many light meter tests concluded this ended up with the brightest picture)

Then I used the 3 screws to make the X & Y adjustments.

Finally, fine tuning the 3 screws with the lens back and with the aid of a light meter.

[Alan Gouger]

Here is a nice video that walks you through the procedure.

https://www.youtube.com/watch?v=aCGh1FVZd9U

[Lee Mannering]

Well done Mark. I'm a little rusty on the GS Xenon servicing now but what a wonderful projector with lots of happy memories of mine in el day.
I was very pleased when my last one went to Si and in good hands a very loved and pristine machine being put to good use.

[Graham Ritchie]

Mark

Just more thing you should be aware of regarding adjusting Xenon lamps, I would not expose the lens to the heat from the lamp during adjustments to no more than say 10 seconds, before closing the dowser if you can with the lamp running on a GS1200. The reason I say this, and I must add that I no nothing about the Xenon GS1200, only cinema stuff I once worked with, is that without a "film" running through the gate, the lens is being exposed to the full light/heat from the lamp. Its ok to do this, but it has to be done in "very" short intervals, otherwise the lens will get hot, With 35mm you can damage the lens if its exposed for two long a period.

What we did with 35mm was a quick burst/adjust, close the dowser, let the projector continue to run for a short while "keep things lens wise cool" then quickly open the dowser/adjust then close within say a 10 second period. With the Simplex we removed the lens altogether and did the bulls eye thing as you mentioned above.

Anyway food for thought, but just be aware of protecting the lens from to much heat.

Just one more thing, and it concerns personal safety, do follow the manufacture recommendation regarding the handling of Xenon lamps, don't forget they are extreme pressure lamps and sometimes if not rare can explode, not often I have only had two go BOOM in ten years at the cinema, but when they go BANG glass and bits and pieces will travel at a high velocity, so at the very least wear full eye protection, never underestimate those things.