8mm Forum: Lamp troubles

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Posted by Mike Peckham (Member # 16) on November 30, 2003, 05:40 AM:

Hello Gang!

Thought I would share this with you; I was watching a film last night and the screen went dark, sound continued as did the projector so I automatically thought 'blown lamp'. I had a spare so popped that in and still nothing.

Could it be a lamp that was faulty from new or problem with the projector? Thinking the latter I took the back of the projector [Sankyo 702] to check for fuses, only found one and that was ok, traced the wire and all seemed to be in order, lamp holder not cracked or burned, hmmm... Found another spare projector lamp that I had taken out of a machine that I had bought sometime ago, I had replaced it because the reflector was shot but kept it because it still worked, popped that in and the lamp came on, hmmmm.... So this morning I went to Jessops and bought a brand new bulb 'off the shelf', popped it in and nothing [Mad]

. I jiggled the lamp holder around, tapped things and closely examined the filament, nothing.

So. I took the lamp out, shined up the pins with a bit of fine sand paper and then put a dab of vaseline on each one. Popped it in and hey presto we had light [Smile]

.

So. The moral of the story is; give your pins a little buff up every now and then [Wink]

Mike

Part two.

Have just been watching a film in order to try out the newly installed lamp and unfortunately the image began to become darker and eventually disappeared. Close inspection of the bulb has revealed that the actual bulb bit where in lies the filament has completely blackened, the filament itself is still in tact as it was still possible to make out a dim glow whilst the projector was in warm up mode.

So. What now? Is it an electrical fault? Is the lamp receiving to high a voltage? [Confused]

If anyone has any ideas I would be pleased to hear them. [Frown]

Mike

[ November 30, 2003, 08:16 AM: Message edited by: Mike Peckham ]

Posted by Kevin Faulkner (Member # 6) on November 30, 2003, 12:45 PM:

Mike, I would suggest that you get a volt meter and check the voltage to the lamp holder. Its also worth checking the condition if possible of the lamp connector itself. It's just possible that the transformer has developed a fault. Have you checked all these lamps in your other Sankyo?
Also check that the airflow through the machine is ok and that the fan blades are turning?
A very strange one indeed but I'm sure the answer is probably looking you in the face.
Kev.

Posted by Mike Peckham (Member # 16) on December 13, 2003, 01:06 PM:

Hello Kev'

Just got myself a multimeter and checked the voltages. There is a constant 16.1 volts at the lamp holder with no lamp fitted. The Lamp is rated at 15 volts so presumably this would reduce its life, I also tested the mains voltage coming in to the house and found that to be 246 volts. The projector only has settings for up to 240 volts so would that be enough to cause the extra 1.1 volt at the lamp?

The lamp holder itself is quite blackened so will need replacing, but I don't know what to do about reducing the voltage. I'm not sure whether it is a fault with the projector or due to the high voltage at the mains socket [Confused]

Mike.

Posted by Barry Johnson (Member # 84) on December 13, 2003, 01:24 PM:

Blackening,in my experience,can be caused by the lamp not getting hot enough and causing premature discolouration and ultimate failure.
If it isn't running at the correct voltage this will cause the phenomena.
As youhave already checked this out,then I would venture to suggest that the lamp holder is,in fact,shot,as a secure contact (almost tight) grip in the pins of the lamp are required for proper power feed..........

Posted by Mike Peckham (Member # 16) on December 13, 2003, 02:29 PM:

Thanks for that Barry, but I'm wondering if I replace the lamp holder will the problem simply reccur because the voltage is too high? Is 1.1 volts enough to drastically shorten the life of the bulb? Is the high voltage at the lamp a result of the mains voltage being higher than the 240 volt setting on the projector? Hmmm.... [Confused]

I have just checked the voltage at the lamp on my GS 1200 and at the high setting it reads 24.4 volts. Again higher than the 24 volt rating of the lamp but is it enough to reduce the life of the lamp? I usually run the GS on the low lamp setting anyway so not so worried about it on there, trouble is, I don't have that option on the Sankyo 702 [Frown]

So many questions!

Mike.

Posted by Tim Christian (Member # 48) on December 13, 2003, 05:33 PM:

The voltage across a lamp holder will always be higher with the lamp out than with the lamp in. Some voltage drop due to current flow in leads and transformer winding is inevitable, so the open-circuit voltage includes these voltages as well.

Blackening is inevitable with old lamps. It is due to metal evaporating from the filament. Only where a lamp fails prematurely will blackening not be noticeable.

Especially with halogen lamps, over voltage will reduce life significantly. The increase of 1.6% (24 to 24.4) is, however, not too serious (assuming the measurement is accurate) and is within normal design tolerances. After all, mains voltages commonly vary by 10% due to demand changes.

Posted by Barry Johnson (Member # 84) on December 14, 2003, 09:58 AM:

Mike: I have never been happy with with the 'low light' setting on projectors.This also applies to my Yelco DS810MT,a fine machine but seems to trash lamps if used on this setting for any legnth of time.
As with the ST series,personally I would forget it even exists and run on full lamp setting,at least this would keep the filament hot.

Posted by Mike Peckham (Member # 16) on December 14, 2003, 10:25 AM:

Hello barry

That really intrigues me, I understood that the low lamp setting was there to prolong the life of the lamp and I generally use it for that reason.

On the GS 1200 and the Sankyo 800s' I rarely use the full flux setting unless I am using a big screen or projecting where there is more than ideal amounts of ambient light, consequently most of the time in my dining room on a winters evening the low lamp setting seems to be fine!

On one occassion I switched the GS to the high setting during a show and the lamp blew instantly [Frown]

, I have been warey of it ever since.

As I say, I'm intrigued and I would like to know more about how voltages and running temperatures affect the life expectancy of a lamp.

Mike. [Smile]

Posted by Tim Christian (Member # 48) on December 14, 2003, 05:42 PM:

According to the IES (Illumination Engineering Society) Handbook, the life of a tungten filament lamp depends on the ratio of rated to actual voltage, to the power of about13. The actual power depends slightly on lamp type, power, etc. This means that increasing the voltage across a lamp by 5% reduces its life by one half.

The increase of 1.6% quoted above gives a life reduction of 19%.

Posted by Ugo Grassi (Member # 139) on December 25, 2003, 12:30 PM:

This is probably right, but you have to consider the progression of the voltage too. I have three Elmo GS1200; to one of these I made a light work to "pump up" the voltage of the lamp on the position II. I added to the transformer four winding to supply the lamp at 25 v. Look the same work here (Elmo page):
http://www.ffr-film.de/Katalog/
The site says to do the work to supply the 250W. but I prefer to over supply the 200W. If you wait 30/40 sec. before to switch on the position II the lamp doesn't suffer. The average life of the lamp on this projector is the same of the others.

The supply at 25v together with a two blades shutter (blade at 45°) give about 500 lux on one metre screen.

Posted by James N. Savage 3 (Member # 83) on December 25, 2003, 02:18 PM:

Mike- I have been using Sankyo's for the past two decades, and this is what I have found: I had been using the G.E. Multimirror lamp, and every now and then, I would have to adjust the pins in the socket to get a proper connection. I later heard about the Osram bulb, which was supposed to give an even brighter image. I installed one, and the picture did appear to be brighter, but after about two feature films, it started going dark and in a matter of minutes, it completely burned out. I ordered another one and the same thing happened again. I have since returned to the G.E. and don't have any problems now. I almost always run films on the brighter setting, as it gives a more impressive image.

I think the Sankyo's are sensitive to certain brands of bulbs, but as I said, the G.E.'s work fine for mine (ST-800). Nick.

Posted by Kevin Faulkner (Member # 6) on December 25, 2003, 04:37 PM:

Hi all, Very interesting answers there and I do agree that i think you do get some premature blacening of the lamp on the lower setting.
I remember years ago (when the tungstan halogen lamps started to turn up in projectors)reading an artical which said that the tungstan Halogen cycle only worked properly at the correct working voltage/temperature of the lamp. The idea is that the evapourated tungstan get re deposited back onto the tungstan filament and not the glass case etc. Well surely this wont be the case when the lamp voltage is dropped by a couple of volts such as in the GS1200/ST1200 machines.
I think that I have to agree with Barry on this one as I think the cycle of the halogen lamp is probably the reason.
I like Barry allways use my lamps at full brightness and they seem to last very well. Kev.

Posted by Mike Peckham (Member # 16) on December 25, 2003, 05:59 PM:

Hello Everyone

Thanks for the replies, I can report that the Sankyo 702 is back in service and all seems well at the moment. I checked the voltage again, this time with a lamp again in place and the reading was a steady 14.7 volts. I cleaned the pins on the bulb with contact cleaner and then sprayed some of it into the lamp holder.

I'm not entirely sure that the lamp holder is 100%, if you touch it when the lamp is on the lamp will go out and a little jiggling is required to make it come back on. I think it was a mistake to use petroleum jelly on the contacts because of the temperatures involved and I think it was this burning off that caused the blackening of the lamp holder and, from what people have said above probably the blackening of the bulb itself.

Anyway, thanks once again for all the good advice. What a great forum! [Smile]

Mike

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