The document discusses troubleshooting a Miller welding machine that was not powering on. The procedures taken included checking the control switch, circuit breaker, control panel, circuit boards, contactor, and internal components. It was observed that two integrated circuits on the control board were burnt and the internal system was very dusty. An expert was called in to fix the identified problems and check for other potential issues.

1. Page 1 of 5
EXP. NUMBER: 01
DATE: 19/12/2013
TITLE: TROUBLESHOOTING MILLER WELDING MACHINE
AIM:
1. To identify the various components of a Miller welding machine
(internal/external).
2. To be able to ascertain the reason for the breakdown of the
machine.
3. To ascertain the possible actions/steps to restoring the Miller
welding machine.
THEORY:
The Miller welding Machine is a manual metal arc welding machine use for
welding metals of various thicknesses. Its working principle is basically
based on electricity and completion of the electrical circuit but it has a
rectifier which switches between polarities (AC/DC) depending on the
work to be done. It also has a Relay which prevents the flow of damaging
current from reaching the integrated parts of the welding machine, in the
welding machine is a transformer which steps down the voltage for use by
the machine, a cooling fan is located behind the welding machine which
helps in cooling the machine by sucking out hot air which is being replaced
by air coming in from the air vent at the front of the welding machine;
cools the transformer and the entire system to prevent over-heating, a
Control Panel/board and Card which carries all the points for the control

2. switches is also located in front of the Miller welding machine. The others
include contactor, Power/Source Cable, Work and Electrode Cable. The
power cable is connected to the circuit which supplies high voltage to the
machine; the transformer steps down the voltage to the right amount for
welding operations.
In some situations, the machine may fail to come up out rightly: The
reason for this can only be ascertained by observing and checking the
different components of the Miller welding machine. One can only check
on the components that he is authorised to as stated in his job
description except otherwise.
Page 2 of 5
APPARATUS:
1. Screw driver
2. Pliers
3. Wrench/spanner
4. AVO-meter
5. Tester
6. Miller welding machine (Serial Number: EN 60974-1)

3. Page 3 of 5
PROCEDURE:
 the control/power switch of the miller welding machine was checked
to know if it was switched on/off
 the circuit breaker (CB) was opened to checked if was on/off, also
the tester was used to check if current is supplied to it.
 The bottom area of the front of the miller welding machine was
unscrewed using the screw driver and opened to reveal the circuit
boards (the control panel and the card).
 The components (circuit boards) were dusted properly.
 The control board was checked for burnt integrated circuits (IC’s)
and bad diodes.
 The card was also checked for burnt integrated circuits (IC’s) and
bad diodes.
 The contactor was checked for burnt fuse, also for continuity using
the AVO-meter.
 The casing of the machine was then opened by losing the bolts using
the proper spanner gauge(s) in order to reveal the internal
components of the Miller welding machine.
 The internal components/system was dusted properly.
 The relay was checked to ascertain its operational status.
 An expert/technician was thereafter called upon to fix the
problems identified and to check for other possible corrections to
be made.

4. Page 4 of 5
OBSERVATION
1. It was observed that the Miller welding machine could not be
powered.
2. It was observed that two (2) integrated circuits (IC’s) on the
control board were burnt.
3. It was observed that the internal system of the Miller welding
machine was very dusty.
PRECAUTIONS
The following precautionary measures were put in place in other to have
safe practical exercise;
1. It was ensured that the Miller welding machine was switched off
and disconnected from the circuit breaker (CB) before it was
opened.
2. It was ensured that the appropriate personal protecting equipment
(PPE) were worn before starting the troubleshooting exercise;
especially gloves were worn to prevent body contact with the
machine to avoid electrocution.
3. It was ensured the limit in the troubleshooting exercise was
specified in order not to attempt the work of an expert/technician.
4. It was also ensured that the workshop was properly illuminated for
the purpose of proper visibility.
5. It was ensured that the AVO-meter was set to continuity before
testing for the continuity of the contactor.

5. 6. It was ensured that the appropriate equipment were used for the
Page 5 of 5
different troubleshooting operations.
CONCLUSION
After the troubleshooting exercise on the Miller welding machine, some
components of the Miller welding machine were identified, the reason for
the breakdown of the machine was determined and the necessary
actions/steps to be taken in order to restore the machine was
ascertained.
TASKS:
Functions of the following in the Miller welding machine:
1. RELAY: THE Relay serves the function of controlling the voltage
entering the welding machine. When there is high voltage, relay
opens the circuit thereby preventing the voltage from destroying
the machine.
2. TRANSFORMER: The transformer in the Miller welding machine
steps down the supplied voltage from 240V to about 80 to 100V
which is suitable for welding operations.