Transcript A powerpoint for testing and fault finding a 555

Unit 5
Learning Objective(s)
L5.1a To understand the need for safe working practices when carrying out
practical electronics
L5.1b To understand relevant electrical and electronic principles
L5.2 To be able to recognise and select components used in electrical and electronic
circuits
L5.3 To be able to construct an electronic circuit and understand its basic operating
principles
L5.4 To be able to test and find faults on electronic circuits
FAULT FINDING
What To Look For
Types Of Equipment
Lesson Objectives
• Learning Task 4: Checking and Testing – P22+
• Learning Outcome 5.4
• To be able to test and find faults in electronic
circuits
FAULT FINDING – VISUAL CHECKS
SOLDERING
POLARISATION
+ve & –ve legs
DAMAGE
If the component is not connected to the
PCB then it will not function.
Also check for solder crossing onto
another component (a SHORT) as this
will affect the circuit.
Ensure that each component has
been put in correctly according to
its connection, i.e. positive and
negative legs.
Take care when putting in components so
that you do not damage them.
EQUIPMENT - MULTIMETER
Select a range with a maximum greater than you expect the
reading to be.
Connect the meter, making sure the leads are the correct way
round.
If the reading goes off the scale: immediately disconnect and
select a higher range.
IMPORTANT
ALWAYS disconnect the multimeter before adjusting the range switch.
ALWAYS check the setting of the range switch before you connect to a circuit.
NEVER leave a multimeter set to a current range (except when actually taking a reading).
MULTIMETER
VOLTAGE
V
We can start by measuring a 9V alkaline battery.
1
If the range is set to les than 9V the reading will
only show as “1”.
Fix the range so that it's 20V, and try again.
SET AT 2V
9.60
For this new battery we get a reading of 9.6V.
Remember that the battery voltage "9V" is just
an average voltage.
SET AT 20V
MULTIMETER
VOLTAGE
Connected in PARALLEL between two points
Connect the BLACK (-ve) lead to 0V
(Normally the negative terminal of the battery or power supply.)
Connect the RED (+ve) lead to the point you need to measure the voltage.
V
MULTIMETER
CURRENT
A
Connected in SERIES
Therefore the Circuit needs to be broken
All the current following through the circuit must pass\through the multimeter.
MULTIMETER
RESISTANCE
You can only test resistance when the device you're testing is not powered.
You can only test a resistor before it has been soldered into a circuit.
Resistance is non-directional
You can switch probes and the reading will be the same.
Ω
CONTINUITY
Ω
IF THE TWO POINTS ARE CONNECTED THERE IS
A READING
Test 1 shows that the two points are not
connected.
Test 2 shows that these two points are
connected
OSCILLOSCOPE
An Oscilloscope is a type of electronic test equipment that allows signal to be viewed,
usually as a two-dimensional graph. Normally these are very small signal values
Voltage
An Oscilloscope displays a Vt graph of
voltage against time.
Time
The Oscilloscope has three main areas, the screen,
vertical section and horizontal section. You do not
need to worry about the trigger, we set this to AUTO!
OSCILLOSCOPE – SWITCHING ON
Plug the oscilloscope into the main and switch on using the
Green POWER Button
The red LED will light up
Alter the INTENSITY and FOCUS accordingly using the small
screwdriver
OSCILLOSCOPE - SCREEN
The screen displays the signal to us as voltage against time. The screen is shown as a grid,
which relates to the settings we choose later.
When switched on you can see the
dot/line on the screen
When working it has a resemblance
to an electrocardiograph (ECG)
OSCILLOSCOPE – VERTICAL SECTION
The vertical section allows us to change the Voltage setting which the oscilloscope uses.
The VERT VAR dial allows us to alter
the magnitude of the setting. This
must start out fully Anticlockwise
The POSITION dial allows us to alter
the level of the output line
The VOLTS/DIV dial allows us to
change the increments of the grid
Here the setting is 0.5V on the
VOLTS/DIV dial
OSCILLOSCOPE – HORIZONTAL SECTION
The horizontal section allows us to change the Time (time base) setting setting which the
oscilloscope uses.
The SWP VAR dial allows us to alter
the magnitude of the output. This
must start out fully Anticlockwise
The POSITION dial allows us to alter
the level of the output line
The TIME/DIV dial allows us to change
the increments of the grid
Here the setting is 0.1ms on the
TIME/DIV dial
LOGIC PROBE
• If you get a steady light you have
found your + or – voltage.
• If blinking you have found a pulsed
or switched signal.
A logic probe is a hand-held pen-like probe used for analyzing and troubleshooting
the logical states (Boolean 0 or 1) of a digital circuit.
There are usually three different coloured LEDs on the probe's chassis;
• A RED and GREEN LED indicate high and low states respectively
• An AMBER LED indicates a pulse