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  • Writer's picturePhilip Jones

Got some trouble that needs shooting? Machinery Troubleshooting that is...

Updated: Feb 24, 2020

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.)


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

know that:

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 and 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.



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.

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