When looking for information about optical comparator machines, you want to make sure that you fully understand how the machine works before you attempt any types of repairs. Never try to fix a machine like this if you don’t know what you are doing. The risk of electrical shock is present if you start trying to repair things that you have no experience fixing.
Don’t think that profile projectors are easy to fix when you have no idea how they work. The key to getting to know how a machine can be repaired is to have a good understanding how what makes it work.
Once you have learned all you can about projectors, you can try to find out what is wrong with any broken ones. Think about what it is doing that is wrong, then you may be able to use troubleshooting techniques to narrow down the possible solutions.