Tracker-2800-2800S.pdf - 第81页

81 5-2. ANALOG CIRCU ITS Analog components and circuits represe nt another famil y of integrated circuit component s and include operational amplifiers (op amps), c omparators, references, regulators, ti mers and man y o…

REVIEW

 Integrated circuits are complex devices that are built using basic electronic components.

 The IC signatures resemble zener diodes.

 There are many causes for IC failures and the Tracker 2800 can display its "health" as resistive

leakage, an open or a short.

 Functionally identical pins on a single IC out-of-circuit will display the same signature.

 The most common point for reference is ground, but V

or another point might give a more

informative signature.

Different logic families exhibit different characteristic signatures.

Applications

Testing for faulty IC’s is one of the more common uses for the Tracker. A technician can compare IC’s

in or out of circuit.

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.

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.