[fredhh47]

People often ask for help with CNCs that are mis-positioning. Sometimes the answer is in the software, such as a corrupted file, or a bad program, but many times there is another, very simple solution. Once in a while, it takes a good whack upside the head to remind me to do something I should be doing on a regular basis, cleaning my machines' circuit boards. I run several older (1980's) Bridgeport CNCs and they all share a common trait. Bridgeport draws in ambient air and uses fans to force it across the surfaces of the controller circuit boards to cool them. In a perfectly clean world that would be fine, but in my shop, there's always a certain amount of dust, metal fines and oil in the air. The cooling air is drawn from the back side of the controller cabinet, which is not very far removed from the work table, and constantly bombarded with chips, mist spray, and other contaminants. The cooling air is not filtered in any way. This is akin to dumping your sewage in a river upstream and drawing your drinking water downstream. The result is that after some time, a conductive film of oil/dirt/metal fines forms on the boards, especially at the bottom edges and on lower IC chips. Conductive films are hazardous to the circuit boards - you might as well throw a handful of metal chips on them. It occurs to me that this can occur with any board in almost any controller or shop computer that is exposed to the general shop environment. Your computer or control circuitry could at this very moment be about to develop some strange problem, all due to the ugly buildup on one or more circuit boards. For instance, without warning this morning, in the middle of drilling a bunch of holes, my CNC took off for parts unknown and kept going until it hit a limit switch. Just prior to that, it had drilled several holes in wrong locations. I pulled out the controller boards and found the usual crust of gunk on the lower extremities of several of them. Some liquid soap, warm water and a toothbrush, applied carefully, removed the gunk, and then they were carefully dried with a gently application of air (NOT hot air) and re-installed. After a suitable warm-up period, the machine is now back in service, without having to call my favorite repair person to come in and charge me $300 to tell me to clean my boards.
My suggestion to anyone, with just about any machine with any sort of positioning problems, is CHECK YOUR BOARDS and clean them if they seem the least bit dirty. Doing this will save those nasty, expensive service calls that always seem to occur when you can least afford the time or the money. As a note of caution, I have to say, do not put wet boards back into any machine, and always be sure they are well rinsed, as soap residue is just as good as oil
at collecting dust and chips. Also, while cleaning, don't force water into switches and be careful not to bend the leads on discrete components like those pesky small disk capacitors on older boards. Be sure to clean the non-component side as well, as the gunk plays no favorites when it collects.
If you haven't seen the boards in your machine in a while, take a close look at them, before a problem occurs. It saves your temper and saves on scrap parts, too. One last thought: avoid "circuit board cleaner" spray. It won't do a very good job, and adds to global warming with some pretty nasty chemicals.

[Ryobiguy]

Can you spray a coat of varnish or lacquer to seal up the exposed conductive traces and leads?

I'm guessing it probably wouldn't work, otherwise, you probably would have heard of it by now.