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Cleaning Contacts In Lighting Fixtures

Published : 5th October 2003


Gentlepeople,

I have some older Arri 800W open face fixtures that do not get alot of work anymore yet I seem to consume the bubbles at a prodigious rate. I assume the contacts have become dirty or worn out. What is the procedure to clean the contacts and how do I tell if they are worn out. I have been told to use acetone or alcohol but not sure how hard I should rub or abrade the contacts to remove the grunge ? Ideas ?

Many Thanks
Tom Gleeson DOP
Sydney



I am not familiar with the fixtures in question, but if they use double-ended globes, I can offer the following : (If they are single ended baby bi-pins, you probably have to replace the socket.)

There is a vicious cycle between heat and oxidation when it comes to contacts...if there is dirt or oxidation on the contact buttons, they cause resistance which causes heat which causes oxidation and arcing which causes heat etc etc

If the contacts are just a bit blackened, you can clean them up with steel wool, very fine sandpaper, or 3M Scotchbrite pads. If you use sandpaper, be sure to finish up with fine enough sandpaper that you do not have big visible scratches in the contact buttons or you will get a rapid reoccurrence of the problem.

If the contacts are really pitted and gouged out, there may or may not be enough material left to form a good contact. You will have to smooth the surface down with sandpaper, emery cloth or similar abrasive. some fixtures use steel contacts, some use other metals that have been plated. If you are cleaning up pitted contacts, you will probably be going past the plating and you will now need to clean the contacts frequently to avoid re-occurrence of the problem.

Frequent cleaning of the contacts with a bit of Scotchbrite pad or steel wool will GREATLY prolong lamp life.

Steel wool is conductive - clean it all up when you are done, and DON"T DO THIS WHILE THE LIGHT IS PLUGGED IN!!!

If the socket ends have consistently overheated, the temper of the metal which acts as a spring to keep the lamp contacts tight may have been annealed out of the metal. If this has happened, you pretty much have to replace the socket, since less than good pressure on the bulb ends will result in heat which will result in...see cycle at top of post. Some double ended fixtures use little springs which, once overheated, lose their effectiveness. Others, like the Ianiro Redheads, use leaf springs (like on a truck) which are a bit more resistant to this problem, but which, if totally cooked, can also lose their temper (which of us doesn't)

Replacing the whole socket assembly is probably pretty expensive, but if it doubles the life of your globes, it may well be cost effective.

Acetone and alcohol are good for removing grease but will not do much good for removing crusty carbon and oxide build-up. You should, however, clean the glass of the globes with alcohol if you have gotten fingerprints on them - the oil in your skin causes the glass to retain heat where the fingerprints are and the glass overheats and fails.

Keep the contacts on the globes clean too - use Scotchbrite or steel wool as with the socket contacts above

Mark Weingartner
LA based



The best thing to do with any lamp contacts that are discoloured, pitted, rusted, or otherwise not shiny metal is to PUT IN NEW CONTACTS. Any other solution is just a short cut to get you through the day. You will never achieve the original surface unless you re-machine the socket and have it re-plated...which would likely cost you more than an new socket. The cost of the lamps that you will lose as a result of bad contacts would have quickly paid for a new socket anyway.

Remember that any lamp that has been burned in a bad socket should be thrown away and NEVER put into a fixture with a good socket. The damage done to the pins of a lamp by a bad socket will cause damage to a good socket. So just throw the lamp away and get yourself a new socket.

Bruce Aleksander
Lighting Designer/Director
ABC/Disney
Houston, Texas



Mark H. Weingartner wrote :

>There is a vicious cycle between heat and oxidation when it comes to >contacts

Mark,

Many Thanks for your considered and detailed reply. Your posts always stand above the "noise" on CML.

Many Thanks
Tom Gleeson
www.cinematography.net



>I have some older Arri 800W open face fixtures that do not get alot of >work anymore yet I seem to consume the bubbles at a prodigious rate

Tom,

DXX bulbs (240v 800w for our 120v cousins) are notorious for short life and certainly the state of the contacts in the "redhead" type fixtures has a big impact on bulb life. When new, the contacts are usually plated (silver?) to reduce oxidising of the copper/brass base metal at high temperature. With use the silver tarnishes which increases the electrical resistance and hence increases the temperature at the contacts. Not desirable.

Initially the contacts are cleanable but eventually the silver wears through. The bare copper can be cleaned but this needs to be done more often - probably with EVERY bulb replacement.

A tool I recommend in every redhead owner's/user's kit is a fibreglass pencil. For countries serviced by UK-based RS Components, their stock number is 514-868 and they are well under A$ 20. (US$ 12?) This tool is also ideal for cleaning the recessed contacts on the DXX and other R7s 'linear' bulbs. These bulbs are often supplied with the tarnish on their silver-plated contacts at no extra charge! Again, silver oxide (black colour) is NOT a good conductor of electricity and a quick rotate of the fibreglass pencil give the bulb a bright future. (Sorry, couldn't resist…Oops, again)

I also use this tool for cleaning brass pins on power plugs - again bright brass is a better conductor than dirty brass so this helps to prevent connector-cancer with higher-powered lights.

One disclaimer - the business end of this tool is metal so its VERY IMPORTANT to ensure one UNPLUGS one's light before attempting to clean the contacts.

Cheers,

Clive Woodward,
twiddles pencils in his sleep,
Perth, Western Australia.



Clive Woodward wrote:

>A tool I recommend in every redhead owner's/user's kit is a fibreglass >pencil.

Radio Shack has these. We used to use a lot of them cleaning the pins of the RAM chips in FDL-60 telecines.

Thankfully those days are past.

Jeff Kreines



Mark H. Weingartner wrote :

>There is a vicious cycle between heat and oxidation when it comes to >contacts

Posts like this wonderfully comprehensive one remind me of one of the great attractions of cinema-verite filmmaking : lights are verboten!

Jeff "push it another stop" Kreines



Clive Woodward writes

>One disclaimer - the business end of this tool is metal so its VERY >IMPORTANT to ensure one UNPLUGS one's light before attempting to >clean the contacts.

Doesn't the 50/60Hz vibro action of the person holding the live cleaning pencil give the contact a better shine?

This could be an appropriate time to mention when I was an apprentice and was cleaning a large motorised disco light which had sustained smoke damage from it's previous home. I was struggling to get good access to the corroded lamp-feed slip rings, so I turned the lamp power off and set the motor to rotate slowly so that I could hold the fine abrasive paper against the rotating slip rings. I duly found out that the lamp was switched on the neutral! (having just spat on the abrasive paper)

The moral of the story is either test, test, test. Or don't get involved in cheap disco jobs with dodgy salvage.

Clive Mitchell
http://www.bigclive.com