8mm Forum: Problems with 150w bulbs

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Posted by Phil Slater (Member # 2388) on December 19, 2013, 04:09 PM:

I have been using my Yelco DS810MT super 8 projector alot recently and have had several bulb failures in just a few months. The projector takes 150w 15v bulbs and I use OSRAM XENOPHOT 64634 HLX EFR.

The one that went today only lasted for a couple of shows (about 2 hours of projection time). At first I assumed I had a problem with the projector, but on inspecting the failed bulbs it seems that they have all gone the same way, the white ceramic bit where the 2 prongs come out has gone a bit like a honey comb, ie full of holes and lost all its strength and with a burned appearance. It just crumbles away when you press on it.

I have just checked 4 unused bulbs that I bought from Blue Cine Tech recently and they are the same. No wonder they keep failing after a couple of hours of getting hot. Has anyone else come across this? I can only assume its a faulty batch. I'll be going back for a refund.

NOTE!! I have just noticed that the boxes for the bulbs that have either failed or look as if they will fail, say DISPLAY/OPTIC LAMP. I have a couple of other new bulbs that look ok, where the boxes say PHOTO OPTIC LAMP. Have I been buying the wrong type?

Posted by frank arnstein (Member # 330) on December 20, 2013, 11:26 PM:

Hi Phil,

I went through a similar experience when about four Osram Xenophot 150w lamps all failed after a short time in a Chinon 8500 that I was using. The lamps seemed to be getting extremely hot.

I tried everything I could think of to improve the lamp cooling including masking up the lamphouse cover and anywhere else that cooling air may have been leaking out on its way to the lamp.

Nothing helped and the lamps still blew after a few days use. In the last episode, the projector had just finished playing a 600' movie and was fully warmed up when I decided to switch it off and take a break.

After about 30 secs into my coffee break, the dichroic 150w lamp reflector exploded into 2 separate halves with a loud bang.

With its cooling air suddenly cut off, the extremely hot lamp contracts unevenly as it tries get rid of its heat during cool-down. In some cases this causes the reflector to crack and other times it just seems to effect the lamp capsule which results in early filament failure.

A way to avoid this problem is to keep the projector running after the movie is finished. Turn the lamp off but keep the cooling fan running until all the warm air being pumped out the exhaust becomes completely cool. This may take 2 or 3 minutes to happen. Do not move the projector till its completely cool.

Since I started doing this there have been no more cases of premature 150w lamp failure in Chinons at Projector Heaven .

So try it if you use a Chinon 7500, 8500, 9500 or any Super 8 projector with a 150w lamp. It could save you quite a bit of money and angst.

Dogtor Frankarnstein

[Smile]

Posted by Barry Attwood (Member # 100) on December 21, 2013, 04:55 AM:

Phil,

I think you should check that your not pumping out more than 15v, as a capacitor or something may be breaking down inside the machine, these are very old machines now, and electrics can deteriorate over time. If you're not sure of checking it yourself, you could always send it to someone like John White. he's very good and reliable (I've been using him for over 25 years now). If you need his number send me an email and I'll send you his phone number.

Posted by Phil Slater (Member # 2388) on December 21, 2013, 05:06 AM:

Hi Frank, thanks for the advice, I will try this. I suppose it could well be due to overheating, it just seemed odd that all the lamps have failed by the white ceramic bit being burned through, rather than the fillament failing.

I have been told that there is nothing wrong with the lamps and it is normal for the ceramic to have small holes, but the bulbs I have seem to have quite large holes. I have a couple of 'older' new lamps where the ceramic part is smooth and hard, as it should be. I'm sure the holes are at least partly to blame for the premature failures.

Posted by Paul Browning (Member # 2715) on December 21, 2013, 10:01 AM:

Hi Phil, I suspect your right to suspect the paste like substance with the holes in as a contributing factor to the premature failure of the lamps. These are filled with xenon gas to help the filament burn brighter and is an inert gas, in a vacuum, which should be void of any oxygen from outside as this will let the gas escape and oxidise the filament inside. A good idea to check the voltage at lamp from transformer in case its being over run, and sometimes the lamp base arc out the pins too, so check lamp holder for loose fitting connections.

[ January 09, 2014, 08:27 PM: Message edited by: Paul Browning ]

Posted by frank arnstein (Member # 330) on December 21, 2013, 07:11 PM:

Hi Paul, Phil, Barry and others here....

I have just examined a 150w dichroic lamp and found that the paste between the lamp capsule and the reflector is only used to locate and secure the lamp capsule and filament in the correct position at the centre of the reflector.

It is a special clay-like paste that withstands very high temperature. It does not serve to seal the lamp capsule airtight as its already been glass sealed during manufacture, so its already airtight.

In fact if you pick all the paste out, eventually the reflector and capsule will come apart. If you then plug the bare capsule pins into the ceramic lamp socket it should still light up as usual. The xenon gas inside the lamp capsule will remain sealed inside the capsule even when the reflector and paste are removed completely.

So you can't judge the lamp by the looks of the paste. Even if it looks porous and has small bubbles in the paste, the lamp could still be perfectly OK because it works independent of the reflector and remains sealed and airtight and should still light up fine. [Wink]

Dogtor Frankarnstein

Posted by Paul Browning (Member # 2715) on December 21, 2013, 07:43 PM:

Frank, Do you think maybe the lamp is vibrating inside the reflector because the paste is not as good as it could be?. I use a lamp similar to this one but its 24v 250w, and these are very reliable, with no special lamp cooling just a standard enclosed fan in a confined space too, which when switched off power to both items is cut. I have had the lamp base fail and this quite common, this burns out the pins quickly by arcing them out. I still suspect the lamp itself not up to spec.

Posted by frank arnstein (Member # 330) on December 21, 2013, 10:08 PM:

Hi Paul,
I don't think vibrations of the capsule is the cause of this.

If the clay/paste was that soft and crumbly, the capsule would probably slide forward when you try to plug the socket onto its pins. Sometimes it can pop right out of the reflector. This usually happens when you disturb what looks to be an OK lamp and socket in order to clean the lamp pins. When you wiggle the socket off the pins, the capsule can become loosened in the clay/paste and then it could slide forwards if modest pressure is put onto the pins when refitting the socket.

You should be very suspicious of the lamp socket itself. These 150w lamp sockets get extremely hot and the contacts inside lose their spring tension and then they can't grip the lamp pins like they used to. Soon they begin to arc inside the socket where you can't see whats happening. Then the lamp filament could blow due to the high resistance of the pin contacts in the socket. Why not replace the lamp and socket with new ones and see if the lamp blowing ceases. ????

When you finish projecting, carry out the proper cooldown practice as mentioned above to get rid of all the heat thats trapped in the lamp reflector. Hopefully that will solve this annoying problem for you.

[Smile]

Dogtor Frankarnstein

Posted by Phil Slater (Member # 2388) on December 22, 2013, 10:30 AM:

Thanks for the comments everyone, I have decided to get the projector checked out.

Posted by Steve Carter (Member # 4821) on June 14, 2015, 07:56 AM:

I thought my 150w lamps were failing, and the clay like substance and a sort of carbon was on pins. I am glad I never threw them away, and since my lens broke, I have cleaned the pins on 'dead' lamps, they are not dead at all they now work. I used a very small diamond file on pins and after several try's being very careful as if by magic they light...

Posted by Alan Rik (Member # 73) on June 15, 2015, 12:20 AM:

I had this happen to a Eumig S940. It would burn out by around the 2 hour mark. I suspected the bulbs but after I sold it the buyer told me he had the machine checked out and it was the machine. It was providing too much voltage to the bulbs!
Yikes!!

Posted by Andrew Woodcock (Member # 3260) on June 15, 2015, 02:36 AM:

It is also a common phenomenon of well used lampholders that become loose around the terminals causing arcing and eventually either eroding the pins on the lamp due to the arcing or causing them to blacken due to the carbon deposits from the arcing/ poor electrical connection surface contact made between the pins and the brass ferrules inside the lampholder.

If this happens regularly and lamps are blowing prematurely, it really is time to change out your lampholder.
New ones fit very precisely and will stop irregular loads damaging your lamp circuit including the transformer.

Remember, there are often heavy currents of around 10amps carried by these circuits, they really don't need even more inflicting upon them.

As Rik says, it is also a good idea at the same time to check the transformer setting on your projector as some people try to squeeze every little bit of extra brightness out of their lamps by feeding them a slightly higher than normal voltage.
This can be done by setting your mains voltage regulator to say 220v instead of 240v here in the uk, resulting in around 9% higher voltage at the lamp.

This of course, will result in a brighter lamp but at the detriment of it shortening the lamp life in the same way that the low lamp setting found on many projectors prolongs lamp life.

Posted by Brian Fretwell (Member # 4302) on June 15, 2015, 06:36 AM:

I don't think I have had the filament of a bulb fail due to worn lamp holders. The bulbs failed due to erosion of the pins until they didn't make contact and almost fell off when touched they were so thin.

Posted by Lee Mannering (Member # 728) on June 15, 2015, 06:46 AM:

Spot on Andrew [Cool]

and one of the oldest faults and probably simplest to fix by replacing the lamp connector block. Remember folks we are talking about quite a bit of current to supply a projector lamp so we need a good solid connection between lamp and power.

Posted by Andrew Woodcock (Member # 3260) on June 15, 2015, 06:49 AM:

The pins do become eroded Brian sometimes through arcing when the lampholder has been used for many years.

I am not saying this is the only cause Brian, just one I have come across on many occasions and once changed for new, the pins then look the same as when installed when the lamp needs replacing after its normal complete lifespan.

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