Text below copied from a post dated May 09, 2005, by an anonymous member, to this thread: http://www.controlbooth.com/forums/general-advice/2233-standard-instrument-maintenance.html. Minor grammatical edits have been made.
Get out the inspection mirror and flash light. The following is hopefully a useful guide to a service call in general. Much of it has already been covered in other parts of the forum, this is the details otherwise. Long winded but in following what to look for and watch for does not in servicing the equipment does not take long. Print it up, then print up a poster size type of sheet with what basic principals you are looking for. Remember that you are looking for problems before they fail as the goal in a good service call. Cleaning and prepping a fixture is one thing, do a real service call or inspection such as the rest of the world in theory is doing yearly and it's a by far different thing.
First the simple - what is easy to notice without much work for the good service call. Look at the fixture, its cord and plug and note anything that stands out. Shake the plug, do you hear its terminals loose within it? Does it work?
1)Look at the plug's strain relief, has it failed to keep the fiberglass or cord's sleeving in the strain relief? Look for suspicious stuff about the plug and the wire coming out of it. Look at the pins and general condition of the plug. If stage pin, are the slots in the pins parallel, with any plug - did someone over spray the pins with paint, are they arched? All would need repair than. You can service a plug but that's a different discussion.
2) Open up a sampling of the plugs of given lot numbers and ensure that screws are tight (1/4 turn past finger tight or the specified torque of the plug) and conductors are not warn or breaking away at both the strain relief and terminal. If you don't have a way of knowing when a fixture was wired, or it would be difficult, error on the side of opening up all plugs when possible during a good inspection.
3a) Make sure that those installing the conductor into the terminal knew what they were doing in the proper amount of wire stripped and inside the terminal. You would not believe how many wires have the insulator also inside the terminal in now making good tension to the insulation of the plug but not so good tension on the conductors. Much less loose terminals, or over-stripped jacket removed from the conducts and thus rats nest of wire within a plug. On a 15amp plug you should see 1/4" between outer jacket of cable and the plug's face, on a 20amp up to ½" but no more. Did they get all strands of wire into the terminal or most with a few haphazardly flinging about inside the plug? (it happens.)
3b) What do the crimps or ferrules look like if stage pin plug? Did someone use the wrong crimp tool or a pair of pliers to smash down on a crimp that later will let the wire pull loose? Is the wire even correct in AWG for the ferrule or terminal in use? Hmm, double up a 16ga wire and it equals three sizes smaller in number or three sizes bigger in dia. In other words, two 16ga wires equal 13AWG. Heat wire don't fold as neatly as copper thus you might in folding it to fit within a 12-10ga terminal or 12ga ferrule fold it and it's now fine. On the other hand, a 16ga wire stuck into a 12ga or 12-10ga opening is about useless. More often than not, even when using a 12ga ferrule, the screw will still cut into the conductor and not support all strands equally. If you find un-safe crimps or ferrules in use, and the conductors are damaged it might be worth your tugging effort in replacing them should they fail. Most stage pin plugs use a #8-32 screw. As long as you get a ring terminal with a #8 stud, there is a variety of ring terminal if not flag terminal sizes based upon the wire not only what comes with the plug. A 14-16ga ring terminal will than fit the conductors properly as opposed to a wire that's the wrong size in the wrong hole. On a ferrule, use say a 16ga insulated ferrule, and sleeve the normal 12ga ferrule over it. You than get twice as much tin over the wire and much less chance the screw will simply cut thru the ferrule. Were your plugs even installed with the proper crimp or ferrule hardware, or were conductors just shoved into holes or wrapped around terminals? Tinned wire can be ok at times, but other than that, that's why you are inspecting. Don't accept crap wiring.
4) Look at the strain relief. Was it too tight in damaging the insulation around the conductors? Has time and wear at this flex point damaged the insulation or conductors in this area? Was too much wire stripped and the strain relief is now bearing down directly onto conductors as opposed to the sleeving or outer jacket? Was it too loose in causing problems with conductors breaking or pulling loose of terminals? Look at how much effect clamping pressure of the strain relief has had on the outer jacket and or conductors. Do they have the happy medium or one extreme of no tension or another of too much pressure and insulation squeezed dangerously out of the way?
5) Look at the cord. What kind of condition is it in? Are there little snags to its fiberglass that might expand with usage that you can glue back down in preventing fraying? Plyobond and other multi-surface adhesives work well in preventing a small nick in the fiberglass from opening up further. Beyond this, are there large holes in the sleeving necessitating replacement of the conductor protection? Fiberglass sleeving is cheap, replace it when it can't be glued tight. Anything larger or similar in size to a 1/4" hole needs replacement or cutting the whip down in length. Examine the conductors themselves at such holes. If SF-2 with a fiberglass braid over it, it might be frayed some but safe, on the other hand it can also hide a scratch that exposes conductors under the silicone insulation. If other than fiberglass braided conductors under a fiberglass outer sleeve, examine them also for what condition they are in. On the cord often non-braided heat wire will last longer, in the fixture and near heat source, the fiberglass braided heat wire will often be superior in heat reflection. Balance your usage of a heat wire by what's provided verses what you find most easy to use. You are not allowed to have a splice within a whip. Any fixtures having splices within the whip need replacement. High Temperature Fiberglass Electrical tape can at times work wonders for quick repairs to whips or work well in strain reliefs, but should only be used if absolutely necessary to do a repair to conductors as a temporary fix. Electrical tape is not rated for high temperature use nor advised for use on a fixture either conductor or sleeve to it. In most cases the Size #0 sleeve is the proper one to be using. Is the sleeving in place too big, or plastic?
If other than fiberglass sleeved cord, you have some that are heat rated and some that are not. In the good stuff - at least VDE that's somewhat heat rated I think to 150c, or better stuff that will have a 200 or 250c rating to it stamped on the cable, have a look at its jacket and condition of the cable in general. At the moment I'm having some suppliers confirm that their heat wire such as Tempflex or Rockbestos is water, oil (fog fluid) and UV rated for exterior use. Often you will find that heat wire cables - in a rubber/silicone sleeve especially Euro VDE types will break down due to oil. Damage to the outer sleeved cable than should be examined for cuts and punctures as above and replaced as above. Heat in the cord touching a fixture and other water, oil, and UV can break down a cable in making it unsafe. UV, oil and water can also break down a fiberglass outer sleeve.
Thermoplastic SJT wire is especially bad where oil from fog gets concerned. Amazing how a little DF-50 fluid will break down a SJT cable. Much less, even if 90c instead of 75c, it does not like to touch a hot lighting fixture without serious danger from now exposed conductors now touching the fixture. Stage and Studio much less movie lights don't use such cable - probably not in the UL listing for application - it's just the cheap DJ club lights and PAR cans used for rock shows that use the wire. Checking with your local building authority on the NEC use of such fixtures when powered by such cords might be a good idea. Even if a factory aluminum PAR can, you might not be able to use the normal cord feeding it on stage if they put any thought into the code. So as with other major or minor projects you might need to replace all fixture cords of one type or another. If I touch a fixture, it's really rare I will re-install a SJT cable on it unless really low wattage thus heat.
Not all brands of heat fixture cable (having inner conductors and outer jacket as one assembly) is created equal. All will work to replace fiberglass sleeved conductors as long as you can attach them within the fixture. While Euro cable - Tempflex and Pro Cable amongst others might be rated for 200C also, but its insulation is poured around the conductors. Often a cut or nick in the outer jacket than once flexed will go all the way down to the conductor. This as opposed to a more SJ seeming American type of cable such as Rockbestos that has a separate outer jacket with filler material surrounding the inner conductors. Rockbestos for heat wire cables is by far superior. Altman and electrical suppliers can get it. General distributors for gear more sell the Euro cable heat wire I less recommend for use even if cheap and rated for the same temperature.
There is 250c wire, 150c wire and 200c wire. 150c wire for other than use as a ground is not recommended in line other than PAR fixtures just as a 90c SJ or SJT cable often won't be of much use. Be cautious about fixtures wired by way of extension cords, often they are going to need a lot of work. For the most part, stick to the 200c rated conductors, be it SF-2 silicone fiberglass sleeved or not, or a 200c rated three conductor cable. 250c Cable while rated for a higher temperature also most often has less flexibility to its conductors and individual strands of wire. In other words, while you can stick it in an oven and it won't melt down, day to day use and flexing on the other hand might break down the conductors. Inside a fixture - especially a Mole Light or Audience Blinder type fixture and other fixtures of very high temperature, you can't do better, but as a fixture whip you can. 250c wire is most often Teflon instead of silicone and when available as a cable it will have a sort of varnished fiberglass sleeving over the cable. Good stuff for permanent install, just don't bend it with constant use.
Do not be overly concerned if your heat wire seems less in AWG rating than that of a normal extension cord. What are these 2,000w Fresnels doing using 14/3 wire on them? Heat wire by its nature will be a little less effected by heat in amperage rating due to its higher working temperature. If that's what the manufacturer specifies to use, its use is correct. On the other hand, some lighting fixtures such as the 575w version of the ETC fixture came with 18ga wire. Once they came out with the 750w version, the 18ga wire was insufficient for the wattage. You must in using a ETC fixture at 750w be using the proper conductor size. While for all other intensive purposes the fixture is one in the same and on the really old versions you can get rid of the alignment nubs specific to the 575 fixture in installing a 750 cap on it, you must change the conductors. Some heat wire you can use for over its thought to be expected amperage, others you don't want to be using. Read and follow the fixture instruction manual and guides on them.
Have I mentioned the use of an exploded pictorial of each fixture you are to work on in being useful? Go to the website and pull up the assembly drawings. This will both save time should you have to pull a fixture apart in re-assembly, and help you to know when someone did a other than factory “improvement” to it. You should have a three ring binder in the service area of the instruction manual and exploded pictorial on all fixtures in use.
6) Have a look at where the cord now enters the lighting fixture. That's another flex point that often will wear out both for outer jacket/sleeve and inner conductors. Beyond that what type of strain relief is in use? Is it a two screw strain relief that often cuts into the conductors, a nylon strain relief that becomes brittle and has too small of a cross section in rubber water tight strain relief to take heat well without becoming brittle or a metal one that's more substantial in taking heat better but can still slip or allow the cable to slide free. A Heyco nylon strain relief often will need to be replaced. A two screw strain relief if cutting into the conductors or sleeving might require you to replace the whip. Fiberglass heat tape will be a good abrasion and flex resistant fix to such strain reliefs. Otherwise properly sized nylon tubing while it's hot will often last well in a fixture in limiting the flex and clamping pressure. On a nylon strain relief you will often find that if the nylon shrunk, became brittle and cut or moved, the little nylon fingers than clamp directly onto the cable and it than is dangerous. The tape will also help in this area.
7) The strain relief itself, is it loose? Especially with plastic strain reliefs, they come loose. A loose strain relief than will allow conductors to twist, move and pull free. That's a bad thing, the conductors should not move about within the fixture other than where needed while focusing the lamp. Get the strain relief tight by hook or by crook (rivet or other method), and when exposed, add high temperature Thread Locker to it to keep it there.
8) Follow the wire from strain relief to lamp base within the fixture. Where exposed such as in a lamp cap, have a good look at it to ensure the conductors don't stretch or overly touch anything such as screws or anything else that can cause bad cooling around it or pull tighter as the fixture gets adjusted. Its common conductors will pull some with use, make sure that you both have slack, yet they don't touch what they should not in having too much slack. If you can't get exposed wire in direct sight, use the flash light and mirror as necessary. Inspect every inch of the wire. This especially near the lamp base as it's the most concentrated source of heat and often where the wire will start to fail. Often in a fixture you will see fiberglass sleeving called spaghetti tubing over the conductors. That's a good thing both to protect from wear on things it might rub up against, and shield some against the heat. If nothing else, where cord enters lamp base, a sleeved wire should it fail than has the extra layer of protection. That's also the general concept of fiberglass outer sleeved silicone wire as fixture whip. Should you be replacing whips or doing work in them, sleeving the conductors if not the high temperature tape is often useful.
9) Some fixtures such as a PAR can will often have a splice inside the lamp cap that goes from heat wire off the lamp base, to what ever type of cord is used. Other stage and studio cans will just use longer leads in a fiberglass sleeve - a better idea. Other fixtures will have auxiliary gutters mounted to the fixture that are slightly cooler to house things like switches, circuit breakers or fuses, if not just patch the wires.
Often the splice will be fine, other times it can use improvement to it - even if factory. Just opened up a Altman CDM outdoor par today. It had 200c wire coming off the lamp base, 250c cord off the fixture, and 90c household grade wire nuts binding the conductors. The fixture itself in only being 150w arc source can get hot still in it being an arc source, but the wiring cavity where the wire nuts were in use were separated from the heat both by way of reflector and secondary plate covering this cavity. I was less concerned about heat - though questioning the use of vinyl wire nuts, and more worried about the wire nut coming loose as often wire nuts will due to vibration or just use.
Do not allow standard wire nuts even in such a fixture. Nylon, Vinyl and PVC all have the same safe operating temperature so don't be fooled by nylon splices either in being better. Primary difference is the other two melt in exposing the conductor, nylon just becomes brittle and as a secondary thing needs to break away before it also exposes conductors. My choice in this instance where heat is less a factor will have been to use something nylon.
Specifically I will have used nylon cap splices that are like a wire nut, but you use a crimp tool to crimp the thing into place so it won't come loose in exposing the conductors or letting them pull free. Otherwise there is lots of high temperature wire nut solutions that either can be hi-temp tapped so they can't pull loose, or have internal set screws over high temperature plastic outer coverings. Depends upon the application.
While a splice within a fixture is preferable to within the cord, it short of having its own area is often dangerous. Look at rock and roll par cans. There is a good reason why the spin the bottle hole is often capped off or there is a knob to do so now. Most of it comes from the splice method and cable. In the past this was made especially hard since often you needed the same PAR can to run ACL in series, Ray Light with wire leads feeding it, and PAR Can lamp with its Mogul Extended End Prong base. MOEP or GX-16d. Given you had to switch, easy to remove methods from spade terminals to using the wire nuts has been done in the past. Now I high temperature splice and high temperature water proof heat shrink tubing over the crimp terminal if not replace the whip. Ensure that especially if SJT cable or lower rated cable, that the fixture whip is not touching the lamp or metal components within the fixture. Air is the key.
If you have a splice within the fixture, note the conductors going into it to see if exposed conductors are falling out of the splice or if it all looks neat and trim with the insulation stopping shortly before the crimp or turned area but defiantly not exposed. Are conductors able to pull out of the splice, are there strands of wire not quite going all the way in, is the fiberglass sleeving becoming loose? Lots of other details you will note up to and including a strand of wire melting thru the wire nut. Do not use vinyl wire nuts within fixtures -replace them if you see them or they will work loose and allow a short. No matter the conductors, don't use something that can come loose. Another type of splice is the push in terminator/tap splice. Such things work well with solid wire, but its foot grip otherwise will cut thru stranded wire. If you have stranded wire going into a push in to grip type of fitting such as used on some stereo equipment speakers, replace it as it's not dependable. Where possible cable tie in a par can where there is a lot of cooling vents, or use fiberglass E-tape to band the wire together. This will take up most of the strain relief from the splice, make for a neat splice and prevent the conductors from moving where they need to be spliced. Keep the tape/cable tie away from the splice so you can see into the splice. Otherwise when you hide the splice by way of tape, it makes those later seeing it suspicious as to what shotty work you are trying to cover up such as too much stripped insulation off conductors exposed.
Another type of splice would be the butt splice. High temperature butt splices as long as covered in at least three layers of high temperature tape, or in the case of a par can - high temperature heat shrink that's water resistant is an option. Always use the correct splicing tools and give a good tug on your wires after splicing them to ensure you have a good splice.
10) Check the ground. Ground conductors can be using lower temperature wire in that they don't touch the heat source directly, and one would prefer to note a melted ground as a warning sign for the rest of the fixture, than have something else fail in melt down. They often will also be a lower gauge of wire in some belief that the current flow temporally in overload thru them will be sufficiently able. That's a factory consideration. When replacing a ground wire, use the same gauge of wire as the conductors.
A melted ground wire, or exposed crimp to it is not a bad thing in all cases. You don't want such a thing where it can touch terminals, but the idea of a ground is that a hot will touch it or the frame first anyway so why insulate it? Architectural lighting fixtures often won't use a insulated ground wire. Insulate where possible but don't be overly interested in over insulation of it as opposed to a conductor.
Check its crimp terminal. If it's all burned up, use a high temperature crimp terminal instead. In general, use high temperature crimps and splices anywhere inside the lamp base area. Replace where oxidized and corroded - you want a good ground path.
11) Check the mounting of the ground. That wire should not be able to move about or twist because this also means a less than safe connection. On a PAR can, that riveted ground will often work its way loose. Same story on a real fixture. The ground will often come loose no matter if rivited or screwed. You cannot use Lock Tight or Thread Locker on conducting screws thus it won't work here - it needs to be all mechanical. In the same respect you also should not be using nylock nuts. Think about nylon verses heat - a nylock nut inside a lighting fixture often won't hold tight in the long run. If necessary you can re-pound a rivet back to tight as a temporary fix, but otherwise need to replace it or better yet go with a screw.
Always a lock washer. But instead of the spring lock washer types, use a internal or external lock washer for better gripping of the conductor. You can use lock washers with rivets. This especially if what you are grounding to is painted. Paint don't conduct well thus some form of displacement of material lock washer between crimp terminal and paint surface can be useful in it both preventing the terminal from moving about and in digging into bare metal.
A good lock washer and nut will work at times better than a nylock nut. Try to avoid washers where your ring termials are concerned. They just act as a pivot easing surface in further loosening up the joint. A external tooth lock washer will both function as a washer and prevent it from coming loose. Beyond this, a toplock nut will both take the heat in mechanically being hard to loosen and add to the resistance of the nut coming loose.
12) Look at the lamp base where the wire goes into it. Is the wire showing heat damage? Are the screws if used to mount wire to lamp base loose? Do they have a lock washer? Are lock washer and screw brass or bronze? A belleville or cone washer will otherwise be acceptable as long as the same metal. Steel tends to corrode and stainless has at times problems with touching other metals such as brass and bronze in otherwise causing corrosion problems. Zinc plated steel once in a lamp base will corrode very easily - avoid its use. On a lamp base, a brass/bronze and perhaps only as one of the two in nickel plating will suffice. Are the crimp terminals showing heat problems such as corroding? Replace in that case with high temperature terminals and insulate them as needed with high temp. tape and tubing. Nothing other than the ring should be esposed. If Fresnel or Medium Pre-focus (P-28s) base, there should be an insulator between lamp base and its mount. Is it in good condition or all brittle and burned up? Have the conductors failed in getting too hot? Exposed corroded conductors coming off the lamp base? This can be because of loose screws or other arching sources, or just heat in general. Cut and replace as needed. Use spaghetti tubing and a small amount of tape as necessary.
13) Look at the lamp base mounts. Are they tight? As above in using lock washers and if needed high temperature Thread Locker will also help. Most important is the metal type. Again brass and bronze in taking heat well, otherwise stainless steel in also taking heat well if not better - just not conducting as well. Even on a PAR can lamp base, how about that screw holding the plates together in its being tight? Should your wire feed into a hole in the base mounting plate, what kind of condition is it in and is that hole a sharp edge? Tape, a silicone panel washer or something to make it work better? On other lamp bases such as mogul screw or medium pre-focus internally, be it rivet or screw are they tight? Some are designed to have a bit of movement, study the type of lamp base for what's best but don't accept loose where not appropriate.
14) Remove the lamp and inspect its contacts. Are they factory or arched and corroded? Are they nickel plated as per new or for the most part clean but blue/black? What the lamp when it's taken out as need be with a pry bar says about itself, it also says about the lamp base in contact with it. Gold plating is great, but also melts down. Otherwise nickel plating is normal. Examine any center point contact plates also. While a screw base to a A-lamp/household lamp might be nice and neat, often that center contact - that should be the hot will get really funky. Is it a smooth surface without bumps and divots from welding? Especially bad will be RSC (R-7s) lamp base types that have a sort of cone contact on each end of the lamp. They just don't conduct well in tension and surface area to conduct with. Surface area - clean surface area is the key to conduction. Blackened and arched lamps in base will have less path of least resistance to conduct with meaning lots of heat and extra heat at those points that conduct better. You can clean lamp base contacts but that's a separate discussion.
Re-install if in good shape the lamp. On a PAR, can you physically lift the lamp by its base, or does it just fall out? Other lamps and bases will have similar relationships from bi-pin to RSC. If that lamp easily gets removed, one bounce while installing or transporting it will also allow the lamp to become disengaged from the base. Such loose contact will also be a source for extra heat as the current tries to flow but has less than optimum tension. Take the lamp back out.
15) look at the lamp in general. Some types will have porcelain around the pinch area. Some will even have a layer of silica sand between pinch and porcelain. That silica sand with a crack allowing it to run right out of the lamp base than is a bad thing. In other lamps, perhaps if the two part porcelain is loose such as in a 5Kw DPY or larger lamp, perhaps more support such as a stainless steel hose clamp will be necessary to keep the two piece lamp base together.
Look at the lamp itself. See any white finger prints or buldges? Much less look at the lamp filament and its supports. Lamps are another discussion as to what you in inspection can live with or need to note in replacing. Clean the lamp with de-natured alcohol and a lint free cloth after looking at it. Such alcohol will also let you examine the filament of a outside frost lamp such as in the case of a FCM cyc light double ended RSC lamp. As long as you are able to look thru the frosting to the glass, you might as well look at the filament.
16) While the pins of the lamp, and the lamp in the base tension is important to note, during a real inspection you need to pull out the flashlight and inspection mirror. You are examining the fixture, so why stop when it's something you can't easily see? Granted a G-4 up thru G-9.5 base such as a FLK/FEL will use will be hard to see the sockets, but give it a shot. Some types of base are servicable (again as a separate discussion) others once they show wear such as blackening. Lack of tension and pitting need replacement. Also throw out the lamp unless it can be saved with work. Some older versions of Fresnel lamp bases allowed the center contact to un-screw some. Should it not provide correct tension, you could screw out a little more to some extent in making it a tighter fit within the socket. Most modern bases won't do this. A edison lamp base on the other hand has a center contact that if not providing sufficient contact can be bent outbound to provide more spring to the contact point. Have a look for arching or discoloring at a specific place on the lamp base - this will tell you where the lamp to base either makes its only contact or no contact. Where possible to service you lamp bases it can be done, otherwise at very least a cleaning with perhaps a thinned out cue tip and some carburetor cleaner will work wonders in removing carbon build up and oxidation. Important to note is that once you have a buffed and serviced surface, or at least one that's chemically clean, you need to coat the now bare metal or it will oxidize worse than if you had not touched it. There is various de-oxidants and coatings on the market discussed elsewhere also.
17) Electrically now your fixture should be in safe condition. There are potential other notes I forget in general or that the manufacturer might state. Specific fixtures also have certain details about them. Mark your fixture in some way with the date and your name. Perhaps grease pencil or marker inside the lamp cap or something. That's a good tracking and quality control type of thing.
18) Fixture itself. Follow the manufacturers instructions for how to clean the lens and reflector much less bench focus it. There will be differences in style dependant upon the brand and type. Such things also have already been discussed.
19) Blow air into and all around your fixture with the lamp removed before you clean reflector/lens. Clean the fixture with Windex or other non-residue chemicals. Otherwise give it a second alcohol cleaning to remove the residue. Note that fresh rags are a good thing. Look for rust. Replacement of bolts, tapping and oiling with a oil rated for the temperature if not tightening them and using thread locker will be needed now. Paint as needed the fixture now that it's disassembled for the most part. Be careful with some of the screws that are stuck. For many of them they will break or strip before coming loose. In cases like that, you have to replace them to the best extent possible. From gel frame clip that comes loose or un-welded to lamp base knob that does not screw in easily, now is the time to check each part and fix them.
20) Have a look at other pivot and working parts such as the yoke mount. Are its screws/rivets tight or loose? Is the locking dog or clutch in good shape and not broken or loose? Replace especially the yoke mounts now as opposed to later. Most will use 5/16" grade 2 screws. These often rust with heat and moisture. Better ones are availiable. The area of the yoke is often what needs replacement. Your fixture should not slip out of its focus even when locked into position without dogging down. If it slips, there is a cause. Can be as simple as turning the carriage bolt on the clutch mechanism 90 degrees or it could be something stripped, broken or loose. Have a look at the non-clutch side of the fixture. Is it stripped? If all such as on a par can that side is attached to is a aluminum plate, it's easy to strip this out. Perhaps a longer screw with side lock nut to prevent it from coming loose - but not so tight it gets in the way might be of value. Such a nut might also be of use on the knob side of the yoke. Remember the falling follow spot issue. If you can't remove the screw, it won't fall. Often on a PAR can, the screw will come with a nut on the inside of the can. Often given this a nylon locking nylock nut. Great idea in preventing the screw from coming loose, bad idea on the nut type, much less given you can't see the nylon not failing how do you know it's still there? On a PAR can, what if you were to feed the screw from the inside of the fixture and put the nut - even if nylock now that it's less in the path of the light, on the outside of the fixture? At that point a missing nut hopefully is noted.
21) Have a look at the lens train or focus operation. Does its rails or slot need teflon oil, white lithium grease or spray on graphite after removing any rust? How does the lens train move about? Is it easy and smooth, or do you have to kick it to get moving? First sand the lens train with say 100 up to 600 grit paper, than as needed add the spray on graphite coating and wipe off the extra. You will be surprised as to how well it works than.
22) Check to ensure your lenses are clean and not chipped in any way that will effect the output. Are they green or blue? Are they the same type of lens as the other fixtures, much less in the correct mounting holes? Clean the lenses say in a dish washer amongst other debated solutions. Also make sure that the proper lenses are both in the proper order in the lens train as there can be more than one size in one lens train. Much less at times lenses while for the same fixture can have been upgraded to a wider but thinner lens. Make sure that if you are buying new lenses that you state how old your equipment is.
23) You have drawings, look for the missing parts from a cone washer replaced by a lock washer to a fiber washer not used at all. Check the condition of the parts on the fixture. Look also hard for loose and missing fasteners if not cracks in the frame. A crack in the gel frame casting can be a bad thing. A crack elsewhere might be acceptable.
24) Should this fixture have an iris, what kind of shape is it in? Perhaps crocus cloth and graphite will help it, or do some of its leafs need replacement? There are only a few different types of iris leafs and they are interchangeable for the most part other than if one of the three. A Lycian M2 follow spot leaf is the same leaf as used on a Altman 3.5Q5 fixture. Ok, such a iris base fixture does not exist but I own one. So if you have a bunch of burning up iris units, perhaps you can buy one and change out what leafs are needed, than clean the rest. A iris burning up in one area more than another means a badly centered lamp but it's too late now.
25) Same with the shutters, as long as they are not bending inward, you can to some extent sand with very fine sand paper, if not even grind a new smooth edge on them that's just slightly shorter in re-using them as long as they are flat and smooth. This is a very specific technique I will infrequently use but for the most part replacement shutters are not that expensive. As with the iris, what is most important is a smooth flat edge to the surface. If it has even a ding in that edge, that's where heat will concentrate in making that shutter fail. Should be a given that if you have to have a shutter in more than say 40% from one side, that perhaps you should re-focus the instrument, but what ever the case, look for heat damage because not everyone thinks. Some you can save and graphite, others you need to replace. Each brand has a different means of getting at the gate/shutter assembly. Much less for instance on the Altman 360q series, it's one of three types of round washer like handle and a specific rivet. Use the wrong rivet and you might wreck that washer.
26) Check the reflector, gate and other parts of the reflector assembly for rust in mounting or plate or rust on screws. Should the fixture get wet, that rust will seep onto surfaces and destroy them further. These after the lamp base and wire will be next to get hottest. If you blow out your fixture and get a shower of micron sized silver confetti, you know that you have a dichroic coating on the reflector that's peeled up. As said, follow directions in cleaning reflector and lenses. Use the wrong cleaning method even on a Alzak aluminum reflector and you can destroy it. On a 5 or 10 degree Leko's plastic lens, that glass cleaner might just scratch it worse than just using alcohol on it to wipe off the dust. On the other hand for say the inside of a scoop, perhaps a fresh coat of high-heat reflective or white paint will do it wonders when not so nice in finish.
27) Fixture for the most part is done in a thorough inspection. You don't have to field strip the fixture, but checking as much as possible even with one's fingers to verify tension is of use. Observe everything, than re-assemble, turn it on and bench focus. Remember that hot patching is a bad thing. Install a in-line switch instead when protected by a GFCI outlet. Different methods for the bench focus and another debate.
28) Check the safety cable. There should be no rust, much less that snap hook needs to snap shut. If it does not perhaps a bit of oil will make it do so, but don't spend too much time in making it snap. Cut up and replace safety cables that don't snap closed. Replace snap hooks also that don't close properly or that have broken teeth to them. There is a debate further in if it's permissible to bend a safety cable's loop to fit thru a ½" hole in the fixture. Such a bend than becomes a weak point in the wire rope, but given the distance of fall, it's probably not un-safe enough. Judge for yourself and look for broken strands or seriously damaged bends or wire rope in general.
29) The clamp is often neglected. Why do factory send a ½-13 grade 2 screw that's only 3/4" long with the fixture? Hmm, loose 1/8" worth of lock washer, and another 1/8" worth of yoke and that's only ½" worth of thread within the C-Clamp. Not enough nor a strong enough screw in my opinion. Even if 7/8" or 1", it's still not long enough. Most C-Clamps will accept up to a 2" long screw, use it. Where possible, replace all C-Clamp bolts with at least a 1-1/2" long screw of Grade 5. No the grade 2 won't break, but as you move up in grade you also move up in rust resistance.
Oil your screws and clamp. Oil without mechanical locking help might make something come loose easier but in this case you are using a lock washer so it's not coming loose. While it is acceptable to use both lock washer and washer on a clamp, the lock washer is what is most important in preventing the bolt from coming loose.
Than again, you need a certain amount of movement without it coming loose. Add a fiber or nylon washer between yoke and the standoff T-nut part of the clamp. Such a free bearing surface will allow you to tighten the clamp, yet also allow the clamp to pivot some without anything coming loose. As with most screws, 1/4 turn past finger tight is proper tension with a 6" C-wrench. You don't need a 10" or larger wrench to tighten a screw. If it comes loose with use re-tighten it or look at the user if more than just a little loose.
The pan-lock set screw on the other hand is of a different material. It needs oil or it's going to rust. Use or or it will rust in place. Gorillas will over tighten and deform the standoff or even break it. Make them extract this screw - it will be a learning experience in something that often cannot be removed. Can be but not always. If you oil and use this screw, it will be by far easier to extract than something that is not used much and rusts into place. Should your standoff get divots in it that allow the fixture to slip some, grind away what you can so it's flat again and where possible spin the standoff away from that area. Otherwise you might be able to get replacement parts. Much less if you have built some side arms, you will have extra parts.
The pipe clamping square head set screw needs to function properly. It often will get dings, need to be removed for the 4" version to be installed so it will clamp to smaller pipes or walls or other wee bit of problems. Never remove this screw without examining the screw. Might be bent and not working properly but look at the tip of the bolt first. When that gorilla with the 10" wrench dogs down the clamp to the pipe, they will deform the tip of the bolt. When you try to remove it from the clamp, the bolt often is harder than the cast iron of the clamp and its removal will destroy the threads of the clamp. That's unsafe. Should you have a damaged tip, re-tap, or cut its tip off than re-tap. Then extract it. Should it be a bent bolt, cut it off at the bend and remove what you can near where it exits the clamp. Attempting to remove a bent screw from the clamp otherwise will also strip out the clamp. Replace with the same brand of set screw.
In assuming a C-Clamp, the technology of the casting has improved much over past years. They still are not perfect. If your clamp no matter if bent steel, cast iron or stamped or cast aluminum shows any sign of bending, replace the clamp. Do not allow in service a bent clamp. While more frequent that it will bend instead of break, you still don't want to continue using it or it potentially will break.
Be watchful of stock looking cast C-Clamps that have a sort of pint/varnish coating on them. They do not come from any manufacturer and instead from china. Such clamps that have this seeming varnish coating are using much cheaper metal in the casting and need that extra coating to prevent the rust. Such clamps with the cheaper metal will break and strip 10x faster than anything a name brand even 40 years ago was making. It's also something that should it get hit might fail instantly at any point. Have a look at the clamp for hair line cracks, but with these cheap C-clamps you might never see the hair line clamp. Do not use some off shore other than name brand clamp. No name on the clamp, varnish like coating to it, toss it in the trash.
Such clamps came on the market say 10 or 15 years ago and only lasted a few years by way of the theater supply market looking for a cheap alternative. I doubt they are still available, but thousands have been sold over the years. Be watchful of such things.
30) CE verses UL fixtures. Be mindful of the world economy. At one point we had a delivery of a hundred or more S-4 PAR fixtures come in on a rush order. They were all metric we found out later. Over 1,400 S-4 PAR fixtures in stock, and other than some sold off and replaced over the years, the metric S-4 PAR still shows up in the inventory at a constant basis. Substitute a M -4 for a 10-32 screw and you have serious problems. Take the clamp off and try to install it on another fixture and you now have a standard ½" screw fitting into a metric clamp. Rock and roll aluminum PAR cans and their clamps are phenomenal in having any number of three - yes three types of hardware in them. Metric, Standard and old English Standard. Think back to the history of China and the orient. If industry was set up during the turn of the century, they in being backwards but catching up might still be using some say antiquated ½" but 12 instead of 13 threads per inch screws. Think about the possibilities of such hardware getting into your own inventory. While you can for the most part if you know your fasteners tell the difference often between a metric and standard piece of hardware - for instance the black oxide type fasteners when metric will have a sort of gloss coating to them, once you get something that is imperial but the wrong thread in being very close into your system you are screwed. Or for us the shop manager that made the choice to not instantly toss out all that hardware screwed us. A bolt might be a bolt in saving money, but once it's mixed in with other bolts you are screwed. Many metric fasteners will be very close in threading to that of a standard thread. Just a wee bit loose or tighter than normal. Be very careful these days and get your theater to purchase screw thread plates to test them with.
Beyond this, should you get a fixture that is metric, take a engraving tool and write metric across its body so those looking to “fix” it don't make it worse. Be very careful about the hardware that is on the clamp or fixture. Very easy to screw up and ruin your world.
A simple, thirty step process anyone can do in his/her own theatre.