HOW TO CLEAN LEMO 3K.93C SERIES FIBER CONNECTORS

A HD signal can be sent well over 12 miles (20 km) of single-mode, fibre optic cable, without the need for a repeater. Wow!!!! Where the cameras are powered over a hybrid cable (like shown above) from the CCU / Base Station, distances of over a mile (2 km) are possible. This is pretty incredible for those of us used to distributing HD signals using traditional copper (BNC) cabling.

Like any technology, fiber has its own quirks. The main enemy is microscopic particles of dust in the connectors. Generally speaking, I find fiber to be less prone to problems than traditional BNC (copper) cables, and more importantly, any problems that do occur are much more quickly apparent. This is a primary reason why I prefer fiber over copper - extra especially for the purposes of off-camera recording. Some fiber systems allow you to precisely monitor the error count in a fiber connection in real time, and therefore you can determine the actual quality of the link at any given moment. You can't do this with copper cabling, or not so easily.

The Lemo system uses what is known as a F2 type contact housed inside the 3K.93C series connectors. The rounded ceramic tips in the F2 contact are referred to as end faces, and the alignment sleeves as ferrules. Simply put, it is basically a polished ceramic nipple inside a alignment sleeve. Its these F2 contacts that need to be kept clean, so they mate correctly and relay the light pulses through the critical fiber optic junction. In the photo above, the F2 connectors are located at the 6-o'clock and 12-o'clock positions. It is essential for the end faces of the Lemo F2 contact to be completely clean and free from any kind of dirt or debris, to ensure the correct performance and operation of the contact.

Its a fact of life that these fibre optic end faces can become dirty in normal use, and therefore need to be kept clean. They are particularly sensitive to contamination by dirt, and especially by dust. Unfortunately, this glass-like material can get dirty easily in normal use, and is somewhat difficult to keep clean because the ferrule sleeve is in the way in one half of the connector. So you need to ensure the end faces at this critical fibre optic junction, are kept completely clean and free from any contamination to ensure optimum performance. The main problem is microscopic dust particles falling on the end faces, when the connectors are open and exposed.

The first rule with fiber, is that if a fiber connection is working normally, don't touch it. In other words, don't do any routine cleaning just for the sake of cleaning. There is always a danger that the very act of cleaning might do more harm than good, and actually cause a connector to stop working properly, that was working previously. So leave well enough alone. A latched connector that is working correctly, will tends to keep working indefinitely while the connector remains latched, or attached to their respective cameras and CCU / base stations.

If fiber is giving errors, the first thing to try is simply to re-plug the connectors. This often fixes the problem, as minute particle of dust may shift out of the way in the re-plugging operation. If this doesn't work, then the next thing to try is cleaning the tips or endfaces of the ceramic nipples inside the F2 connectors. You'll need to assemble a fiber cleaning kit for this purpose, and follow the cleaning procedure described below.

A fiber cleaning kit consists of the following items:

(1) a special tool for removing the two metal sleeves inside the (smaller) FUW connector, to expose the tips of the fibre optic ferrules inside.

(2) Some clean cotton buds (not too large in size). You need lots of them (I use 4 to 6 per connector half for each cleaning operation, so 8 to 12 for a whole connector).

(3) Pure alcohol for cleaning the tip or end face of the fiber optic ferrules (i.e. for soaking the tip of the cotton buds with alcohol before use).

The correct alcohol to use is Denatured, Industrial Grade 99% pure ISOPROPYL ALCOHOL. It is also referred to as "S -grade" Isopropyl Alcohol (IPA). You should not use commercially-available Isopropyl Alcohol which is usually diluted with water and a light mineral oil. This leaves an oily, thin-film deposit behind on the tips of the fiber optic ferrules, which is not desirable. You also shouldn't use commonly available, ethyl alcohol based products. So generally speaking, don't use commercially available, or medical alcohols, such as "rubbing alcohol" etc. etc. Strictly speaking, "rubbing alcohol" is ethyl alcohol, but the term "rubbing alcohol" has become a general non-specific term for either isopropyl or ethanol rubbing alcohol products. In the US, "rubbing alcohol" is defined as 8 parts by volume of acetone, 1.5 parts by volume of methyl isobutyl ketone, and 100 parts by volume of ethyl alcohol. In any case, none of these relatively impure alcohols are good for cleaning fiber (i.e. unfortunately, the types of alcohol that are the easiest to get hold of).

However, in an emergency, I would resort to using any type of alcohol you can get your hands on. If it gets you back up and running, this is preferable to having the system down (i.e. the lesser of two evils). The Makeup Department or Paramedic on set often has some sort of alcohol on hand that could be used in an emergency. You can always re-clean the fiber ferrules later with the proper ("pure") industrial isopropyl alcohol, as soon as possible afterwards. This will get rid of the residue left behind from using incorrect alcohol products. I always finish up by thoroughly wiping the fiber tips with a completely dry swap as part of the cleaning operation (described more fully below). Extra especially if using impure alcohol products. This helps to get rid of any residue or film deposits left behind by the evaporating alcohol. You are essentially cleaning glass, and we all know how tricky that can be in practice (i.e. to get glass 100% clean is virtually impossible). Cleaning fiber connectors is more akin to keeping camera lenses and filters clean on set, so this is perhaps a better way to view this procedure.

You are also advised not to try cleaning fiber connectors by blowing into them, especially with compressed air. I assume the reason is this causes the microscopic particles of dust to build up inside the connectors by forcing the dust particle deeper inside, where it can potentially cause even more frequent problems later on. But again, in an emergency, I wouldn't be adverse to a little (gentle) blowing if it gets you back up and running quickly when you need to shoot right away. There is an area about the size of a pin point where the two convex fiber ferrules connect i.e. just touch each other at a tiny point. If a microscopic piece of dust is sitting on this spot, the fiber signal is impaired when the connector is snapped together. If the signal is impaired (has multiple errors), most fiber systems resort to a hierarchical system to give the most important signals running in the fiber priority. Usually, the video image is given the greatest priority, and gets through the fiber as cleanly as possible at the expense of "less important" signals, such as audio or paintbox control. This is why you sometimes get an nice looking image on your monitors, but no paintbox control, when you first plug the fiber in to the cameras. Simply re-plugging the fiber cable often fixes this problem (especially re-plugging on the camera end). I always try this first, and repeat if necessary. If that fails, then I try cleaning the F2 ferrules inside the connectors next.

The Cleaning Procedure for the F2 Ferrule Endfaces inside Lemo 3K.93C series Fiber Connectors:

Here is an overview of the cleaning operation, followed by a more detailed step-by-step instructions. As seen above, there is a larger and a smaller fiber optic connector (e.g. PUW and FUW) In the larger PUW connector, the tip of the ferrules is exposed, and easy to locate and clean (they are glassy and white in color, like little ceramic nipples). However, in the smaller end of the connectors (FUW), the tip of the two ceramic ferrules sits at the bottom of two metal sleeves, preventing easy access for cleaning. So you need to remove (pop off) these sleeves (there are two in each connector). Using a special tool described below, screw it into each sleeve in turn, and pull. The sleeves will pop off. This leaves an opening big enough to insert the tip of a cotton-tipped cleaning swap (cotton bud). Soak the end of the swab with ("pure") industrial isopropyl alcohol (IPA), insert it in the opening, and clean with a gentle wiping motion. You may need to rotate (or spin) the tip, if the head of the cotton bud is relatively large in size (smaller buds are preferred).. Use another, fresh cotton bud soaked in alcohol to clean the adjacent ferrule. One wet cleaning per ferrule endface should be enough. If in any doubt that the ferrule is cleaned properly, then simply repeat by cleaning each fiber ferrule endface a second time, each with a fresh, alcohol-soaked cotton bud. Finally, finish the cleaning operation with a completely dry cotton bud. Gently wipe (or rotate) the tip of the fiber to remove any film residue left behind by the evaporating alcohol. It is important to remember to always use a clean cotton bud every single time. Don't use the same swab to clean more than one ferrule tip at a time. I normally use 4 to 6 clean cotton buds for each half of the connector, as described below (so 8 to 10 for both sides of the connector). If in doubt, use more clean swabs and keep cleaning until satisfied the job is done thoroughly (wet followed by dry). After cleaning, quickly pop the metal sleeves back in place, and unscrew the special tool (one side at a time). Either cap the end of the connector immediately to prevent further dust getting inside, or quickly snap the two cleaned ends of the connectors together ready for use. If for any reason this cleaning procedure doesn't fix the problem, you can always try repeating the cleaning operation. There is always the chance that a cotton bud has deposited more contamination than it has removed. Even after cleaning, the tiniest speck of dust in the wrong place (even microscopic in size), is all it takes to stop fiber connections working properly.

I will now describe the cleaning process, step by step, in more detail below:

1. Working from the open end of the connector, screw one of the internally-threaded ends of the extraction tool onto one of the F2 alignment sleeves (located at the 6-o'clock and 12-o'clock positions in the photo above).

2. Turn 5 to 6 times in a clockwise direction, until the alignment sleeve is fully screwed into the extraction tool. Don't try and tighten it.

3. With the connector and tool held firmly, slowly but firmly pull the tool away from the connector in a straight line to remove the alignment sleeve.

4. Once the alignment sleeve has been removed from the connector, leave it on the end of the tool and put aside. Be careful to keep it clean and away from possible dirt contamination.

5. Soak the tip of a clean cotton bud in IPA (pure Isopropyl Alcohol). Gently clean the tip of the ferrule endface with a wiping motion. Use each cotton bud once only (i.e. one fresh bud per ferrule) to minimize the risk of cross contamination.

6. Since the alcohol leaves a residue, use (another) dry cotton bud to finish the cleaning operation. Thoroughly dry and lightly polish the ferrule endface with the dry bud, again with a wiping motion.

7. Once cleaned, insert the alignment sleeve back into the connector, ensuring the tool and sleeve are in a straight line with the connector, before gently pushing them together until the sleeve clicks in to place.

8. In a counter-clockwise direction, carefully unscrew and remove the extraction tool from the connector.

9. Check that the alignment sleeves have been correctly replaced. Make sure the tip of both sleeves are almost flush to the insulator, and that they are level with each other.

Ensure both of the mating pair of connectors are cleaned at the same time, as contamination from contact to contact is possible. So both halves of the connector should be cleaned at the same time.

The procedure for cleaning the other half of the connector is the same as described above, but omitting the removal of the alignment sleeve. The ferrule endfaces are exposed in the other half of the connector, and are easily accessible for cleaning. See the PUW connector, pictured above foreground left. The white-ceramic, ferrule endfaces are clearly exposed for easy cleaning (the white, glassy tips).

Once you get used to it, cleaning fiber connectors is really quite simple and straight forward, but it pays to be extra careful and a little methodical to get the best, most reliable results.

Here are details about the special, double-ended tool for the removal of alignment sleeves in Lemo 3K.93C series fiber connectors. The Lemo part number is DCS.F2.035.PN. There are other manufacturers of these extraction tools apart from Lemo. The cost is about US$22. Here is a link for one supplier (Mouser) headquartered in Texas:

http://www.mouser.com/search/ProductDetail.aspx?R=DCS.F2.035.PNvirtualkey64510000virtualkey736-DCSF2035PN

Lemo also makes a comprehensive fiber-maintenance tool, part number DCS.91.F23.LA. It combines the extraction tool with an alcohol dispenser, plus a storage area for clean cotton buds. Its all in the one compact unit that you can carry in your pocket, or hang from a belt. If you are running around cleaning a lot of fiber connectors, this devise adds a measure of convenience.

Sony is another place you can get this tool. Their part number is: J-6480-010-B and the price is about US$62 each. You can order it online from this Sony website: https://servicesplus.us.sony.biz/sony-parts.aspx Delivery time is usually 2 to 3 days.

An Alternative: Telecast's MX Series Fiber Connectors

Telecast's MX Fiber Connector use a fundamentally different design to Lemo Fiber connectors. The MX system uses tiny lenses, in what they call expanded beam technology. Whereas Lemo connectors rely on aligning fiber cores to within extremely fine tolerances, the MX connector uses tiny lenses to optically expand the mating interface area. The beam of light from the core of one fiber is expanded to approximately 2,000 times its original size, then is refocused back into the fiber of the mating connector. There is no physical contact between fibers, or between mating lenses. This minimizes the effect of dust, debris and even mechanical vibration. This often means a more reliable connection because of the much larger mating area at this critical interface. These exposed, and therefore easily accessible, lenses are extremely easy to clean. Cleaning is simply a matter of wiping off the lenses with a lint-free cloth (similar to cleaning a camera lens). There are no recesses to trap dirt, or ferrule sleeves to remove. Also, all MX connectors are "hermaphroditic", meaning you never have to worry about running your cables backwards. They are also physically smaller than Lemo connectors, and both 2-fiber and 4-fiber connectors use the same low-profile MX housing. One complaint I've heard about using MX connectors in the field, is that they are difficult to connect in cramped spaces, and especially in low light, as it can be difficult to line up the two halves of the connector for mating. The Lemo system is easier in this regard.

Disclaimer: While I check the information presented here as thoroughly as possible (...through actual work experience, personal testing, and consulting other experts in the field), I can not absolutely guarantee its complete accuracy. These writings really reflect my own evolving understanding of these particular issues as I try and piece everything together myself. These pages are works in progress, and will be corrected and updated as new information comes to hand. Any and all feedback is very gratefully accepted. Especially any information that helps to correct outright mistakes in this presentation, or additional information that helps to expand the scope of these discussions.

Copyright © Peter Gray (November 11th, 2007)

Peter Gray
(in California)
P.O. Box 5132
Pine Mountain Club, CA 93222
United States of America
telephone: +1(661) 242-1234

dp@petergray.org