Tracker-2800-2800S.pdf - 第82页
82 Pin 2 –Input Pin 3 +I nput Pin 6 Output Figure 5-10 . Signatures of a n Op Amp (741) at 10V, 50 , 60Hz with Common to Pin 4. Pin 2 -Input Pin 3 +Input Pin 6 Output Figure 5-11 . Signatures of a n Op Amp (741) at 20V…
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5-2. ANALOG CIRCUITS
Analog components and circuits represent another family of integrated circuit components and include
operational amplifiers (op amps), comparators, references, regulators, timers and many other
specialized functions. These components and circuits present more troubleshooting challenges that are
unique to this particular family of ICs.
OP Amps
Frequently, each pin of an op amp creates a different signature on the Tracker 2800. This signature is
the result of the internal design of the chip and both the internal and external circuit elements
connected to it. This type of analog component typically has many internal junctions connected to each
pin and each pin may also be connected to numerous external components.
The following example will demonstrate ASA with a commonly used 741 type op amp. In this case it
is configured as an inverting amplifier circuit as in the schematic below.
Figure 5-9. Op Amp Symbol and Schematic Diagram of an Inverter Circuit.
We will examine the signatures of this analog IC and present some troubleshooting concepts for this
type of component.
OP Amp Signatures
Do the following to display the analog signatures of an op amp:
1. Select the 1K, 15V, 60Hz.
2. Place or clip the black test lead from the Tracker 2800's Common jack to the IC's ground or a
power supply pin. For this example, the negative power supply pin of the 741 is pin 4 and the
positive power supply is pin 8.
3. Use the red test lead from the Tracker 2800's Signal jack and probe each pin of the IC.
4. Observe that the signatures of each of the op amp's pins are unique.
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Pin 2 –Input Pin 3 +Input Pin 6 Output
Figure 5-10. Signatures of an Op Amp (741) at 10V, 50, 60Hz with Common to Pin 4.
Pin 2 -Input Pin 3 +Input Pin 6 Output
Figure 5-11. Signatures of an Op Amp (741) at 20V, 10K, 60Hz with Common to Pin 4.
Troubleshooting OP Amp Circuits
Troubleshooting an op amp in-circuit may be very challenging. These circuits usually have numerous
connections that act as feedback or compensation loops. This results in almost an infinite number of
possible analog signatures. Use the comparison test method when troubleshooting op amps in-circuit.
In this case, components on a suspect board are compared to those on a known good board. The
Tracker 2800 can help locate the defective component quickly.
The op amp has three main terminals; + input, - input and output. An alternative way to perform ASA
on the op amp is to connect Tracker 2800's Common terminal to the op amp's output while making a
comparison with the red test probe to the “ + ” and then the “ - ” leg. This eliminates problems
encountered when probing op-amps that are isolated from power and common. When there is more
than one op amp in a package, compare one with the other. The dual op amp and quad op amps are
very common. This technique also works with comparators.
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Linear Voltage Regulators
Voltage regulators are commonly found in many electronic assemblies. Some of the most popular
integrated circuits of this type are three terminal devices like the 7805, a +5 volt DC regulator. The
next figure shows the schematic and pin layout of the 7805 regulator. Different manufacturers
implement their products with different topologies and manufacturing processes. So it's not unexpected
that the same functionally equivalent component from different manufacturers may have different
signatures.
Figure 5-12. Diagram and Symbol of a Linear Voltage Regulator, 7805 Type
Input pin Output pin
15V, 1K, 200Hz with Ground Pin to Common
Figure 5-13. Signatures of a 7805 SGS Thompson Voltage Regulator
Input Output pin
15V, 1K, 200Hz range, Ground Pin to Common
Figure 5-14. Signatures of a 7805 Motorola Voltage Regulator
Review
Integrated circuits are complex devices that are built using basic electronic components.