Service Technicians are exceptionally skillful and often seem to work miracles, but despite this, they are only human...any help you can provide will help them get your system up and running. Here are a few ways you can help.
Keep a log
Put everything in writing. It helps to have a certain pad of paper for this purpose, which all users of the equipment know about. Keep it by the console, dimmer racks or some other convenient place. If you start keeping a log after the problem has been happening for a while, try to fill in as much about the previous occurrences as you remember.
Be specific. Note down which circuits, pieces of equipment, or parts of your show are affected. Describe the symptoms specifically so someone who hasn't seen them will recognize them. Does it happen exactly the same way every time? Can you reproduce them? One of the most valuable services an end user can provide is to figure out how to reproduce the symptoms they are seeing. If you can make the equipment fail while the electrician is on site (or tell them how to reproduce it back at the shop) the troubleshooting process is greatly speeded.
Do the symptoms only occur when you reach the same point in a certain show, or use a particular sequence of key presses or lighting events? Does it happen every time?
Which lighting system equipment is on? Which is off? Did anything get turned on or off at the exact moment the problem occurred? What about equipment not related to the lighting system? Are you getting any error messages or lights on any equipment? Which equipment and under what circumstances?
Have there been any electrical storms or lightning strikes? Have any computers or other equipment in your building been affected by such events recently? How about static electricity? Do you get static shocks from equipment in the area? Or, is the air abnormally humid for some reason?
If you know the equipment has had problems in the past, or has recently undergone a repair or upgrade which might have affected it, make sure your technician knows of these events. It may shed some light on the equipment's current behavior. Also, has the equipment been sent out on the road a lot? Has it been dropped? Have any liquids poured in, even years ago? It's also important to note down whether the equipment has been subjected to harsh working conditions: high heat, sub freezing temperatures, inadequate air flow, high levels of dust or sand, and so forth.
What else is going on in the building, or on the same block, at the time the symptoms occurred? Examples are construction work, welding, electrical work, etc. Sometimes large electrical disturbances can affect your system if you are sharing electrical supply with other people in the building, or other buildings on the block. Is this during a peak electrical usage period, such as in the summer when everybody is using air conditioning? Less voltage supplied by the electrical company can result in lights not appearing to be at full. Loss of one phase of your three phase power will result in a partial loss of lighting.
Try to figure out if any reoccurring symptoms are related to certain times of the day. Do they only happen at night? Around the middle of the day? On certain days of the week? When the air conditioning cuts in? Also, was there some obvious point at which the problems started occurring, or did it start happening so gradually it took a long time for anyone to notice? Are the symptoms continuous? If intermittent, about how often does it happen? Ten times an hour? Ten times a week? Only once or twice ever? Did the system ever work correctly, or has this problem been occurring ever since day one?
When you are trying to get an accurate picture of what is happening in a system, valuable information can often be gained from other people. Have the equipment's other users noticed the symptoms? Perhaps they have additional information. Bystanders may also have noticed some of the symptoms. You might be able to ask others for help in nailing down your symptoms. For example, if you are keeping an eye out for a flickering light problem, you could ask actors rehearsing on stage to point to the light if they see it happening.
Try to provide some estimate of how sure of each piece of information you are. If you saw the problem happen with your own eyes, you are probably very sure. If some things were seen only by someone not very technical, the technician will still want to know about it, but you should qualify by mentioning you're not really sure of the data. A technician is used to juggling concrete facts with maybes and coming up with a solution that fits all the information.
Eliminate the middleman
Does the problem happen to everyone? Only one person? Arrange for the technician to talk to them directly. If nobody who has experienced the problem first hand is available during regular business hours, explain this to the technician and ask to set up a time after hours when they can get together. Getting the first hand information is valuable enough to be worth going to the trouble.