Got some trouble that needs shooting? Machinery Troubleshooting that is...
Updated: Feb 24
One of my guiding principals in life is that if someone else can do something, then I should be able to figure out how to do it too if I train for it and work hard enough at it. A person with grit and determination can outperform a more intelligent person with less drive every time. This definitely applies to troubleshooting machinery. Below is a picture of an antique machine lathe. This type of lathe is still in use in most machine shops even if they have modern CNC milling machines as well. (CNC is an acronym for computer numeric controls, I will get into that technology in another post.)
In order to excel at repairing machines of any type, you must understand their purpose and how they are supposed to operate. Many machines such as the one above have oil for coolant and lubrication that is sprayed on the parts being worked. This oil gets into electrical parts like limit switches for end of travel or protective guards. Oil can be enough of a conductor to short out or make a connection on a switch. There are also small metal clad cables that can get pinched or crimped. The motor starter and transformer may be original to the machine and as such are subject to failure due to age. Whether it is a lathe or a mill or an extruder or any of the hundreds of other machines you may encounter, the basic rules you can use to repair them remain the same. Over the last four decades, I have developed my own set of troubleshooting rules that I found helpful. I had them written on paper for many years, but a few years ago I finally wrote them out in electronic format to share.
Philip Jones © 2017
Technical troubleshooting Tips:
TALK TO THE OPERATOR (Person who usually uses the equipment). While they may
have an idea what is causing the problem, take any ideas they have with a grain of salt
so they don’t steer you in the wrong direction. Get the history of any other problems
they have had or that other technicians may have worked on recently. The operator has
many details of how the machine is supposed to operate, symptoms that showed up
before it quit working, and the history of the machine. It is your job to interview that
person to sort through the clues to get to the ones that may tell you exactly what the
cause of the problem is. Ask them what it was doing when it stopped working. Make
sure you understand all of the controls and what they do when the equipment is working
GET THE INFO. Find and photograph the nameplate(s), Ladder diagrams and
schematics Study them to understand the equipment. If unable to find all the info, use
the internet to search the model number and brand for a pdf file with of wiring diagrams. If no luck, call the manufacturer to get a copy of the drawing and to ask technical questions. If a machine or system is confusing to you, many times the manufacturer has free technical
assistance over the phone or internet. Do not be afraid to utilize these resources.
MAKE NO ASSUMPTIONS. 99% of the time, the problem that seems impossible to fix
is due to faulty assumptions on the part of the technician. We assume that the cause
can't be certain things, but we never prove these assumptions. Devise a list of possible
assumptions. Some ideas are: Check incoming voltage, loose wires, fuses, reset buttons,
terminations, hot spots, visual check for burned places, smell check for burnt smell.
Example of an assumption: The thermostat must be good because it is reading
temperature. (It may have a bad relay on its control board.)
DEVISE TESTS TO ELIMINATE YOUR ASSUMPTIONS. The best way to solve a
complex control problem is to prove all the things that are not the cause and remove
them from consideration. This process of elimination will narrow down the options until
the cause is identified. WRITE DOWN EACH TEST AND RESULT.
NEVER USE A FUSE AS A TESTER. If you keep blowing fuses when troubleshooting, you are doing it wrong. You will run out of fuses before you find the short circuit and it is an expensive and amateurish way to troubleshoot. Ohm’s law will tell you if your control fuse is going to blow when you energize the circuit. (BTW: OHM'S LAW, LEARN IT, KNOW IT, LIVE IT) Your ohm meter is the best way to trace a short. With your circuit de-energized, mark and remove all the load wires from the fuse which was blown. Test each one to ground (if the control circuit is grounded) and neutral and pick the one with the lowest resistance to ground. Since electrons will follow the path of least resistance, this is the direction the short circuit traveled. Continue to follow this wire till you come to another termination
and repeat the process of mark, remove, and test to ground and neutral. Eventually you
will reach the point of the short circuit.
TAKE A BREAK. If you have been working on the same problem for more than two hours, you are probably bogged down. Take a break for at least 10-15 minutes or a
lunch, get some fresh air. Your mind works best when not under pressure. An
overnight sleep can also work wonders for your logical thinking ability.
DON’T OVER STRESS. Customers always want quick results and can sometimes
hover over you and distract you from thinking clearly. Find a way to tactfully let them
1. You will will find the problem and you will not stop until you do.
2. You will maintain communication with them to make sure the cost is manageable.
VERBALIZE THE PROBLEM. Often you can solve complex problems simply by
describing them to other technicians. This other technician may be even less
experienced, but the act verbalizing helps to sort out the possible causes of problems.
A SMART PHONE is a great tool, but it can often become a crutch that keeps you from
thinking critically and methodically to solve the problem. Don’t call for or search online
for help until you have done the steps above. Youtube videos can be great to show
how to make a repair once you have identified the issue, but they rarely help with
KNOW A GUY. When it comes to any problem or project, it is great to have a list of
experts that you can turn to for help. Develop a contact list of smart technical people
that you can call on for knowledge base. As a last resort , call one of these folks only
after you have followed all of the above steps.
WEB RESOURCES: Sites like hvac-talk.com and mikeholt.com have many threads
that can help to pinpoint issues, but the problem is that they also have many false leads
and downright bad information. In order to use these types of resources successfully,
you will have to learn to filter through the chatter and ignorance of some postings.
1. OVERHEATED TERMINATIONS AND/OR WIRING. Make sure the breaker or
fuses, overloads and wire are sized correctly and all terminals tight.
2. VOLTAGE. If your motor is overheating and or making a louder noise than
usual, it may be getting improper Voltage. Always check Voltage from line to
line, and then from line to Ground. On three phase, A-B, A-C, and B-C should
all read very near the same.
3. AMPERAGE. If a 3 phase motor is running, check the Amperage on all three
leads; They should read within 10% of each other as a rule of thumb.
4. RESISTANCE. Check the load side of the starter with your Ohm meter from
line to line all three ways. This is the easiest way to test the windings of the
motor. They should read very near the same. NOTE: Your meter should be
set on the lowest scale. Test all the leads to ground; you should get infinity or
OL (open lead). If you have a Meg-Ohm meter, check from the leads to
ground and verify the insulation is good.
5. MECHANICAL. Another possibility most people overlook is bearings and the
load itself. Many times the load has increased due to bad bearings either on
the motor or on the load it is moving. Sometimes, the motor is being pushed to
do more than it is rated for and causes it to overload.
Notes: Don't Be afraid of learning new things. Most technical devices are not as complicated
as they first seem. Take it step by step as you learn new things. Read documentation, look up
part numbers to find out how each component is supposed to work. Nowadays the internet has
more information than you need to understand just about anything...and a whole lot of useless
information to send you in the wrong direction. Just jump in and get busy - with your brain :)
Philip Jones © 2017
Access Service Team, Electrical & Mechanical Services
TEML 18183 TECL:18282 TACLA:76916C
Don't Give Up! If you never stop trying, you can't fail.