CET Section III

When looking at waveforms in a switching power supply which of the following should not be done?

• look at waveforms in the primary circuit and the secondary circuit with one probe and with its ground lead connected to the respective ground
• look at the control signal of the switching device
• connect one probe ground lead to hot ground and the other to cold ground
• vary the input AC voltage

What Vcc should be observed in TTL circuits?

• 3 V to 15 V
• 5 V
• 12 V
• +/- 15 V

If a unit under test is dead what is the most logical area to check first?

• the power supply
• the output device
• divide the unit in half and begin in the middle
• begin at the input and trace to the output

To look at a high frequency, high magnitude waveform across a component(s), neither side of which is at chassis common, the oscilloscope would be used:

• in the AC coupling mode
• in the DC coupling mode
• in the invert/add mode
• by plugging the oscilloscope into an isolation transformer

If a defective Hall-effect sensor is suspected check:

• the continuity of the coil in the device
• that current is being supplied to the device
• that the window in the device is not dirty and light is being blocked
• that the internal magnetic bias in the sensor is strong enough

Refer to Figure 1. The output of this circuit will be:

• nearly the same pp signal as the input with the opposite phase
• nearly the same pp signal as the input with the same phase
• a larger pp signal than the input with the opposite phase
• a larger pp signal than the input with the same phase

On the schematic of the unit you are testing you note that the word reset on the microprocessor has an overbar. The condition on that pin, at power up would be expected to be:

• low and stay low
• high and stay high
• low and then go high
• high and then go low

What happens when a sine wave signal is input to a non-inverting op-amp circuit if the feedback resistor is open?

• no observable symptom
• reduced output
• output at only positive and negative saturation
• an overheated op-amp

If a diode in a bridge rectifier opens, the observable symptom is:

• no observable symptom
• increased ripple and decreased dc output under load
• the opposite diode in the bridge will fail
• the primary fuse will be blown

What might be used in a triac circuit to lessen the chance of turn on by a sharp increase in the off-state voltage.

• a snubber
• a varactor
• a metal oxide varistor
• a kick back diode