Film-Tech Forum ARCHIVE: Gah! Can't get bulb out

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Posted by David E. Nedrow (Member # 4981) on 04-09-2011, 01:16 PM:

I was going to change our bulb out today, but CANNOT get the cathode out of the support assembly. This is in a XENEX II. The existing bulb is an Osram, which I'm swapping with a CXL-20R. THe Osram was put in by our tech. I completely removed the cathode lead holding screw, just in case something was catching on.

I pulled on the cathode as strongly as I could, eventually using two hands. I carefully tried to twist the cathode and the support at the same time, but no go.

Should I take the bulb and cathode support out and (safely) break the bulb to work on loosening it? I do have a backup bulb, in addition to the new bulb.

Thoughts?

Posted by Chase Pickett (Member # 5975) on 04-09-2011, 03:16 PM:

PB Blaster the S.O.B! Just kidding. [Roll Eyes]

What do you mean by you tried twisting the Cathode and the support at the same time? Were you going the same direction, or opposite? Honestly, I would pull the bulb and the support out together and break the bulb, just to inspect what may have happened. Now for some questions: What wattage is the bulb? How many hours are on the bulb? What amperage do you have the bulb set to? Was the screw fastened all the way? And finally, What is the use of that projector like?

Posted by Aaron Mehocic (Member # 15) on 04-09-2011, 03:16 PM:

I had a similar problem about four or five years ago. Removing the cathode support may be your only option and don't expect that after breaking the bulb the stuck piece will suddenly come loose. You may indeed have replace the support.

quote: David E. Nedrow
I pulled on the cathode as strongly as I could, eventually using two hands.

Realize that if the bulb had pulled out and you were exuding that much force, it certainly would have crashed into the anode support or the front of the housing and exploded in your hands. That was a very bad idea. [Confused]

Posted by Richard May (Member # 2627) on 04-09-2011, 04:49 PM:

Aren't there 2 screws on the cathode side?

Posted by Kyle Cranney (Member # 6198) on 04-09-2011, 04:50 PM:

I've had this happen to me on a few occasions with both the CXL-20 and comparative Osram bulbs. On the second of these occasions, we actually did end up breaking the bulb before we could get it out. All of the other times I managed to force the bulb to twist just enough that I could slowly get it out, and it did take quite a while.

Posted by David E. Nedrow (Member # 4981) on 04-09-2011, 05:04 PM:

Note that I'm wearing gloves with long gauntlets, and eye/face protection when doing this.

I twisted the cathode support and bulb base in opposite directions, to no effect.

I only started pulling hard on the cathode base when I decided at worst I'll just be replacing the bulb, which was my intent from the start. [Wink]

We' are a two projector setup, but unless I'm running an archive print, or it's the last night of a show, I run from a Kinoton spool tower. We do four shows on Saturday and Sunday, and one-two per week night. This bulb has a LOT of hours on it, and has gotten dim and cranky.

One oddity I noticed as I was taking the cathode lead off was that the support base wasn't inline with the bulb base. There's a slight gap, and I mean slight, between the base and the cathode support on one "side". Just to check, once the leads were off, I rotated the bulb and could see that part of the assembly move up and down as I rotated the bulb. So clearly, the bulb base and cathode support aren't quite aligned.

I only saw one screw on the cathode support. Maybe there's one I'm not seeing that is the problem. The lens focus knob is connected to the cathode support by a long screw, but I wouldn't think that would impact this.

Posted by Monte L Fullmer (Member # 2797) on 04-09-2011, 05:15 PM:

the allen setscrew that locks the cathode pin in place in the holder, hopefully can turn so the end can come out.

Hope that setscrew didn't arc inside from being loose and welded itself to the holer.

Otherwise, it's gonna have to be drill out, hole retaped and new screw.

Posted by Chase Pickett (Member # 5975) on 04-09-2011, 05:29 PM:

Monte, I'm also thinking that it did arc and welded the end of the cathode inside the support. If the bulb wattage is larger, say 5k or higher, there is enough amperage to melt metal given there was a pretty unresistant path to ground. [Eek!]

Posted by Aaron Mehocic (Member # 15) on 04-09-2011, 06:57 PM:

I've seen that happen as low as 2K and I'd bet that is exactly what happened. When I teach young guys to change bulbs I always tell them to mind the gap and take every effort to eliminate it.

Break the bulb, remove any glass chards, cut the cathode flush with the base and keep it on your desk as to show the next generation of what not to do. Make sure when you buy a new support assembly you get the same diameter as the one you are using now. I assume you probably have the smaller of the two sizes, but double check anyway.

Posted by David E. Nedrow (Member # 4981) on 04-09-2011, 07:06 PM:

Monte,

When I opened the non-operating side to take off the cathode lead, I found that it didn't have the allen screw one would expect. Someone had switched it with a hexagon bolt at some point in the past. Even better, people had clearly used pliers to take this is and out, so the head was misshapen enough that neither a socket head or appropriately sized wrench would fit over/around it. So, I also took the pliers route. Ugh, and of course, there's limited space to deal with that.

I'll replace that with an allen head on this change.

This is a 2K bulb, if it matters. Now you've got worried about it being welded in. With no way of getting it out now, short of smashing the bulb and throwing a pair of vice grips on the bulb base, I risk getting it out and breaking the bulb, just to end up with no way to install the new bulb. Darnit.

Maybe I should order a replacement cathode support before I do the bulb.

Posted by Randy Stankey (Member # 64) on 04-09-2011, 07:26 PM:

If somebody replaced the screw with the wrong part then used the wrong tool to tighten it, there's a good chance the threads are bunged up.

If that's the case, there's a good chance the screws were not tightened properly when the lamp was installed. Over time, heating and cooling cycles might have caused the connection to loosen.

The lamp very well could be welded into the socket or, at minimum there is a lot of corrosion around the lamp base, causing it to stick in the socket.

I think you would be wise to order another part before you made another attempt to remove the current lamp. Just take the whole unit out, cathode and all. Replace all the parts with proper fasteners and tighten them properly.

Then, after you have the lamp house working the way it should, take the original parts outside and try to separate them. If you can salvage any of the parts, label them and put them into storage for later use.

If somebody screwed your projector up so badly, this time, they'll surely do it again. When they do, you'll be ready.

Posted by Joe Redifer (Member # 3) on 04-09-2011, 08:25 PM:

It could have indeed arced if it was installed incorrectly with a bit of space left between the back of the bulb and the assembly. If that's the case, it's welded together and you will need to replace parts in your lamphouse. When I first arrived at my last theater, I found a removed xenon bulb that had the back of a Christie support assembly welded on just laying in a box in the corner. You could tell what happened. I can't guarantee this is your problem, but if it is, make sure someone else who is more qualified puts the bulb in next time. Even then, it might not be the tech's fault. Did anyone rotate the bulb during its life? If so, that may have created the gap which caused the arc.

Posted by Louis Bornwasser (Member # 3063) on 04-09-2011, 08:47 PM:

Remove bulb and adapter.

Install protective device.

Put cathode adapter in vice.

With screws loose, then apply channel locks only to the last 1/2 inch of the bulb right next to the adapter. Twist and remove.

Or ship it to me and I'll do it. Louis

Posted by Monte L Fullmer (Member # 2797) on 04-09-2011, 10:09 PM:

Wonder if there is a glass reflector in that lamphouse where you don't want to bust the bulb in there...

..If you take off the negative cable off of the igniter, the you could take the bulb out, get it in the cover then work on that cathode connector...

or, get the bulb covered, take it outside to bust it, then you can see what you can do, for I had to do that with an old Xetron console setup where the anode spider support allen setscrews had indeed welded itself to the spider.

Posted by Mark Gulbrandsen (Member # 72) on 04-09-2011, 11:36 PM:

One of the problems with Xenex lamphouses is that many of the adaptors are made of alumnium. The dissimilar metals tend to disagree with each other and they weld themselves together. I've had to replace many cathode adaptors over the years in Xenex lamphouses because of this. They are not that expensive... nor is the whole lamphouse for that matter. Brass is the best material for the adaptors as it doesn't react with dis-similar metals like alumnium does and it can take the heat better.

In Kyles case the damed cathode support on the SLC Christies becomes so compressed over the years that you literally have to spread it apart at the joint to be able to unscrew some lamps. Also, if you do not tighten them down sufficiently the negative end of the lamp remains loose in the threads and it then also welds itself in place.