ATT Block 1 Week 2

A basic full-wave triac phase shifter circuit can be used to reduce power from ____ __ __ of the input power.

100% to 0%

If the firing angle in an SCR power control circuit equals 38°, the conduction angle is ______ ________________.

142 degrees

firing angle and conduction angle always equals _____.

180°

When Multivibrator Troubleshooting check the following: 1. Output(s) 2. _______________________________ 3. _________________ 4. Transistors 5. ___________________

2. Input Trigger (if applicable) 3. Vcc 5. Circuit Resistances

To troubleshoot an SCR circuit: 1. Determine the type of circuit. 2. Determine if the input signals are correct. 3. Determine if the SCR is good. 4. __________________________________________

4. Isolate the problem component.

The tuner block selects one RF out of many and converts it to an IF of __________ ___.

455 kHz

A Full-Wave Triac Phase Shifter can reduce the supplied AC voltage to ___ of the initial power level.

85%

To determine correct operation of blocking oscillators or sawtooth generators: A. __________________ B. check the transistor. C. Then check circuit resistances with a multimeter, noting any parallel paths. D. _____________________

A. measure the output, D. After the fault is repaired, verify normal operation

Triacs can be used with __, ___, and ___.

AC, +DC, and -DC

The purpose of a UJT oscillator is to change __ power to __ power.

DC, AC

The average voltage applied to the load equals the RMS value of the input sine wave times the conduction angle divided by 360°.

Eavg = Erms x C*/360*

Field effect transistors have three elements ____, _____ and ______.

Gate, Drain, source

Push-pull amplifiers are power amplifiers that have: __________________, ____________________, _______________________, and ___________________.

High current gain, high efficiency, low output resistance, and low distortion

The common collector push-pull amplifier uses one ___ and one ___ transistor.

NPN, PNP

If Ig is applied to the gate and Ia drops below Ih The SCR turns __ and then ___.

ON, OFF

SCR trigger circuits are used as electronic ______ __________.

ON/OFF switches.

The tuner block has three circuits (__ _____________, _________ _____________________, and ___________) combined into one.

RF amplifier, local oscillator, and mixer

in UJT oscillators, Q1 remains OFF until the charge on C1 increases to Q1's __________________ _____________.

TURN-ON voltage

The IF amplifier block has one or more stages of ___________________. All stages are tuned to 455 kHz.

amplification

Once the gain (output) has been calculated, the next recommended op-amp troubleshooting step is to measure the output of the ___________.

amplifier.

An ________ ohmmeter is used to completely check out an SCR.

analog

FETs are tested with an ___________________ or the _______________________ of a digital multimeter.

analog ohmmeter, diode test function

SCRs can be checked with an ____________ ___________.

analog ohmmeter.

Schmitt triggers change input signals of _________ ____________ ________________ into square wave pulses of constant amplitude.

any shape amplitude

Free-running blocking oscillators produce an output when power is __________.

applied

The detector block recovers the intelligence audio and provides ___________ _____________ ___________ _____.

automatic volume control (AVC)

To troubleshoot a FET amplifier: a. Determine amplifier operation. b. __________________________________________ c. Determine if FET is good. d. _________________________________________

b. Determine if Vcc is present. d. Isolate problem to bias circuit.

The amount of current flow is determined by the PN junction ___________ _________.

barrier size

In a Schmitt Trigger, anytime the input is _____ ___ _________, the output is low.

below the threshold

Triacs can allow current to flow in ______ ____________.

both directions

Once the output has been measured, the next recommended op-amp troubleshooting step is to compare _______________ ___ _______________ ___________

calculated with measured values

The gate forms a __________ between the source and drain.

channel

In a Schmitt Trigger, if the transistors check good, measure _________ _______________ with a multimeter.

circuit resistances

A shorted SCR acts like a __________ ____________, ON all the time.

closed switch

The number of degrees after the SCR turns ON is the _______________ ___________.

conduction angle.

A Schmitt trigger is faulted when the output is a ________ _______ ___________ _________ and the input exceeds the threshold.

constant high or low

The purpose of AVC is to maintain a __________ ________.

constant volume

Increasing the reverse bias Vgs ______________ Id.

decreases

in UJT oscillators, When Q1 turns ON, C1 discharges until the voltage ____________ __ _______________ Q1's TURN-ON voltage. The cycle repeats, producing a sawtooth wave.

decreases to below

In power reduction circuits, both ______ and ______-________ ___________ provide circuit protection.

diacs, four-layer diodes

The output of a ________ ________ with a gain of one should be the (+) input minus the (-) input.

differential amp

Perform junction tests of the transistors with an analog ohmmeter or __________ ___________ _________ when testing Schmitt Triggers.

digital junction tester

The purpose of the heat sinks attached to Q2 and Q3 is to ______________________.

dissipate heat

The gate controls ________ ______.

electron flow

FETs are biased in many ways. Biasing does two things: Place a positive voltage on the drain to ______________ current flow and Reverse bias the source to gate PN junction to _____________ current flow.

establish, control

Schmitt triggers use ___________ to ensure short rise and fall times of the output signal.

feedback

The arrow on the gate indicates the type of ___.

fet

The number of degrees before the SCR turns ON is the ________ __________.

firing angle

In a FET, the resistance is low only when the PN junction is ____________________

forward biased

When measuring the resistance of an SCR, the resistance is low only when __________ _________ and after a gate signal has been applied.

forward biased

There are two basic types of blocking oscillators: _______________ and ____________________

free-running and triggered.

Increasing Vcc causes an increase in _______________ on the output of a blocking oscillator.

frequency

in UJT oscillators, R1 and C1 determine the _____________ of the oscillator.

frequency

When a multimeter is used to check out an SCR, the ______ ____________ is supplied by a jumper from the anode to the gate.

gate current

Triacs are also used in different switch applications, such as _____ ___________ _____________.

high current switching

Most faults in multivibrator circuits cause one output to always remain ____ and the other to remain ___.

high, low.

Decreasing the reverse bias Vgs ____________ Id.

increases

In a faulted monostable or bistable multivibrator, you should ensure that the ___________ ___________ is correct.

input trigger

Transconductance is the measure of how much control the ______________ _____________ has on the ______________ ____________ and is measured in mhos.

input voltage, output current

A four-layer diode is made up of one SCR with its gate connected ______________.

internally

When triacs instead of simple resistive devices are used in power reduction circuits, the benefit is _________ ______.

less heat

Schmitt triggers are also called ___________ ___________.

level detectors

in UJT oscillators, Checking for normal operation requires comparing _________ ___ ___________ frequencies.

measured and calculated

Holding current in a SCR is defined as the ___________ Ia required to sustain current flow.

minimum

push-pull amplifier are used in the final stage of __________________ to drive low resistive loads.

multistage amplifier

To reverse bias an SCR with a multimeter, the test lead connected to the meter's __________ ____________ is placed on the anode.

negative potential

The output of a summing amp with a gain of one should be the ____________ ______ of the inputs.

negative sum

in UJT oscillators, R2 and R3 are used to develop the _____________ and _________________ going pulses.

negative, positive

After a triac has latched, removing the trigger voltage will have __ ___________, allowing the triac to continue current flow.

no effect,

When a triac does not allow current flow through it, it resembles an _____ _________.

open switch

The most common fault in a FET amplifier circuit is a failed FET, either _______ or ________.

open, short

If you suspect a faulted op-amp, check both ________ _____________ with an oscilloscope to ensure smooth DC.

operating voltages

When troubleshooting op-amps, first determine the _____________ ________________ of the op-amp.

operational configuration

If a fault is suspected in a Schmitt trigger, check the input to ensure it _____________ exceeds the threshold.

periodically

The voltage applied to the gate turns ON the SCR for a _____________ of the forward bias alternation of the input waveform.

portion

N channel FETs operate by placing a ___________ ____________ on the drain and ______________ _________ the gate to source PN junction.

positive voltage, reverse biasing

The amount of time that the SCR is ON determines the amount of voltage, and consequently the amount of _______, to the load.

power

Triacs, along with SCRs, can be used for ____________ ___________ and high current switching.

power reduction

Diacs and four-layer diodes are used as triggering and __________ _____________.

protection devices

The purpose of an SCR power control circuit is to ________ and __________ the amount of power applied to the load.

rectify, control

With the SCR forward biased, the SCR turns ON. If Ia is larger than Ih, the SCR _________ __.

remains ON

If you determine that the op-amp is faulted, _________ the op-amp and verify correct operation.

replace

A triac consists of two SCRs connected together in _________ with their gates connected together.

reverse

During the __________ ______ ___________________, the SCR is turned OFF.

reverse biased alternation

The reset circuit turns the SCR OFF. When S1 is closed, C1 _________ ____________ SCR 1, interrupting anode current flow.

reverse biases

UJT oscillators produce a __________________ wave and two pulse outputs.

sawtooth

The purpose of blocking oscillators is to produce _______, _____________ timing pulses.

sharp, narrow

The most common fault in SCR circuits is a ________ __ __________ SCR.

short or open

Electrons enter the FET from the ______ and leave from the ______.

source , drain

The audio amp amplifies the audio to a level that can drive a ___________.

speaker

In a Schmitt trigger, if the input is correct, check Vcc to ensure proper ___________ ______________.

supply voltage

AM receivers have four functional blocks, ___ _____, __ _________, ____________, and _____ _____________.

the tuner, if amplifier, detector, and audio amplifier.

The common emitter push-pull amplifier uses ___________________.

transformers

The diac is used with the _____, and the four-layer diode is used with an ___.

triac, SCR

Triggered blocking oscillators require a ___________ __________ to produce an output pulse.

trigger pulse

The input is applied to the gate. Ig is developed, which will allow the SCR to ____ __.

turn ON

Ia current flow is applied to the load when the SCR ________ _____.

turns ON.

In a Schmitt Trigger the input must reach an _________ _____________ ___________ for the output to go high.

upper threshold level

Power to a load is controlled in an SCR power controlled circuit by the amount of time that __________ is applied to the load.

voltage

In an Op-amp, a problem exists if the measured gain or output is off by more than ____ of your calculated values.

±10%