| Copyright 2003, controlretrofit.com. Nuisance faults One of the most aggravating issues facing a machine owner, maintenance tech or operator is showing up to work and firing up a machine that displays a checksum error or a memory failure or any other faults that are not on the machine side, and are aggrevating and frustrating and show up as a control fault. We have received 100's of memory boards, CPU'S, Eproms, processors, and we rejected every one. We take the time to place them on the test bench, fire the IC's as required, and show they are operating properly. Being the honest people we are, we do not ship a new board to the client, we ask them to do a couple of diagnostics in the field over the phone. Because we are sort of friendly, we will work with you as the owner or your techs to resolve the problem. What is the problem? 99% of the time we trace it back to the power supply. So your techs are reading a 5.1 VDC signal at the power supply? The majority of the modern, say the last 20 years, manufacturers have test points on the board to find the voltage available to the components. You may find a 4.8 or so voltage on the test point. This is a result of resistance in connections between components. It is a result of oxidation and deteriation of contacts. Clean these contacts to increase voltages to the board As a trained electronic tech, you should ask this question. What about the amperage? Good one, you are on the way to being very sucessful and quite rich. This is the stumbling block that hangs many a good man with a good heart. Test the amp output of the power supply. How do you do that? Acquire the test equipment that will allow you to record the milliamp output of the power supply. Also remember Ohms Law. In a pinch, increasing the voltage will increase the amperage. This will fight the resistance that will build up over time. Be very careful. When the control was manufactured they have a little trick. They only put so much smoke in. If you let too much out, you will hit your limit. At that time expect total control failure. It has always been our belief that they should put just a tad more smoke into electronic components, it would make many a techs life so much more rewarding. Grounding The biggest issue with the digital controls seems to always revert to grounding. We spent 3 frustrating yet fruitfuldays on a new 5 axis machining center that the manufacturer had sent out on 3 different occasions a tech, a senior tech, and the original system engineer and the machine would run for an amount of time then would fault out on an axis overcurrent. The OEM abandoned the machine. After consulting with all involved, we were asked to debug the system. What we found was a grounding issure that may not by typical of all machines produced yet stumped the OEM. All manufacturers have optional equipment that they tag on to the machine in hopes that someone will buy it. This machine had the ability to cool the spindle gearbox for greater accuracy through thermal control. However the end user did not desire or need this option. Although the control manufacturer was informed of this decision, they placed this into the control and merely deleted the inputs which would have faulted should the gearbox overheated. While disabling the fault inputs, the outputs were ignored. So when the gearbox achieved a temperature fault, an output was generated that energized a coolant unit, powered by a 3 phase circulation motor, that was the option that was not utilized. By the OEM electrical routing print, the 3 phase motor wiring ran in close proximity to the encoder cables from the axis that would fault. Making a long story short. The original purchaser of the machine sued the manufacturer of the machine, and the dealer who sold the machine. And won. And retained possesion of the machine. The machine was sold at auction, was purchased by a machine tool dealer who offerred it out at a highly reduced rate. We saw the machine and encouraged a small shop to invest the money in the machine, we diagnosed the problem, repaired it and are more then proud to show you a many hundred thousand dollar large travel 5 axis machining center with a total investment of under $40,000 including rigging. If the OEM engineer would have used sheilded cable, routed the 3 phase through a different panduit then the encoder cables, and followed simple industry acceptable wiring practices, our client would not have a $300 an hour productive machine in his shop and the stress and frustration that allowed him to get this caliber of machine for the small investment would never have been possible. It has not only allowed him to produce his own product, it is such a fine machine he has booked over 2 weeks per month to other companies and is saving them money while enjoying a 67 day payback on his original investment. Set Ground Rods! To not set a ground rod next to any CNC machine is a mistake. I argue with engineers and the NEC quite often. The idea that a ground rod contributes to a ground loop is a failure of the NEC to control the engineers who fail in the original design of the digital control in relationship to primary voltage wiring. All ground rods to be effective have to be set correctly. Because the installation is defective on many occasions should not be set as a criteria to alter the purpose of the ground rod. In the analog age a 20 ohm resistance may have been acceptable. We now see 0.3 ohms as unacceptable. The reasoning is that in the micro circuits of todays modern controls, and with the use of the high frequency, 0 ohms is unacceptable yet perfection is hard to achieve. An 8' ground rod was your daddy's ground rod. 20+' ground rods may be needed to achieve a continuous ground throughout your facility. Never ground a shielded cable on both ends!!! Always ground to the control side as opposed to the machine side!!! When using high frequency controls, never derate a neutral or grounding conductor!!! Be careful!!! Harmonics when dispersed through a proper ground will never corrupt data!!!
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