How to use an oscilloscope

The use of oscilloscopes in the process of home appliance maintenance is very common. Through an oscilloscope, you can visually observe the waveform of the circuit under test, including shape, amplitude, frequency (period), and phase. You can also compare two waveforms to quickly and accurately find the cause of the fault. Correctly and skillfully using an oscilloscope is a basic skill for novice maintenance personnel.
Although there are many brands, models, and varieties of oscilloscopes, their basic composition and functions are similar. This article introduces how to use a general oscilloscope.

1. Panel Introduction
1. Brightness and Focus Knob
The brightness adjustment knob is used to adjust the brightness of the light trace (some oscilloscopes call it "brightness"). The brightness should be appropriate when used. If it is too bright, it is easy to damage the oscilloscope tube. The focus adjustment knob is used to adjust the focus (coarseness) of the light trace. It is best to use it when the image is clear.
2. Signal Input Channel
Common oscilloscopes are mostly dual-trace oscilloscopes, with two input channels, namely channel 1 (CH1) and channel 2 (CH2). They can be connected to the oscilloscope probes respectively, and then the oscilloscope housing is grounded, and the probes are inserted into the part to be measured for measurement.
3. Channel selection key (vertical selection)
Common oscilloscopes have five channel selection keys:
(1) CH1: Channel 1 is displayed alone;
(2) CH2: Channel 2 is displayed alone;
(3) ALT: Two channels are displayed alternately;
(4) CHOP: Two channels are displayed intermittently, used for dual-trace display when the scanning speed is slow;
(5) ADD: Signal superposition of two channels. In maintenance, channel 1 or channel 2 is often selected.
4. Vertical sensitivity adjustment knob
To adjust the vertical deflection sensitivity, the knob position should be adjusted according to the amplitude of the input signal. The value indicated by the knob (such as 0.5V/div, indicating that the amplitude of each grid in the vertical direction is 0.5V) is multiplied by the number of grids occupied by the measured signal in the vertical direction of the screen to obtain the amplitude of the measured signal.
5. Vertical movement adjustment knob
Used to adjust the position of the measured signal light trace in the vertical direction of the screen.
6. Horizontal scan adjustment knob
To adjust the horizontal speed, the knob position should be adjusted according to the frequency of the input signal. The knob value (such as 0.5ms/div, indicating that the time per grid in the horizontal direction is 0.5ms) is multiplied by the number of grids occupied by the measured signal in one cycle to obtain the period of the signal, which can also be converted into frequency.
7. Horizontal position adjustment knob
Used to adjust the position of the measured signal light trace in the horizontal direction of the screen.
8. Trigger mode selection
Oscilloscopes usually have four trigger modes:
(1) Normal (NORM): When there is no signal, there is no display on the screen; when there is a signal, it cooperates with the level control to display a stable waveform;
(2) Automatic (AUTO): When there is no signal, a light trace is displayed on the screen; when there is a signal, it cooperates with the level control to display a stable waveform;
(3) TV field (TV): used to display TV field signals;
(4) Peak automatic (PP AUTO): When there is no signal, a light trace is displayed on the screen; when there is a signal, a stable waveform display can be obtained without adjusting the level. This mode is only used in some oscilloscopes (such as CALTEK CA8000 series oscilloscopes).
9. Trigger source selection
Oscilloscope trigger sources include internal trigger sources and external trigger sources. If an external trigger source is selected, the trigger signal should be input from the external trigger source input terminal. This method is rarely used in home appliance maintenance. If you select the internal trigger source, generally select channel 1 (CH1) or channel 2 (CH2). It should be selected according to the input signal channel. If the input signal channel is selected as channel 1, the internal trigger source should also select channel 1.

II. Measurement method
1. Amplitude and frequency measurement method (taking the calibration signal of the oscilloscope as an example)
(1) Insert the oscilloscope probe into the channel 1 jack and set the attenuation on the probe to "1";
(2) Set the channel selector to CH1 and the coupling mode to DC;
(3) Insert the probe tip into the small hole of the calibration signal source. At this time, a light trace appears on the oscilloscope screen;
(4) Adjust the vertical knob and horizontal knob to stabilize the waveform displayed on the screen, and set the vertical fine-tuning and horizontal fine-tuning to the calibration position;
(5) Read the number of grids occupied by the waveform in the vertical direction, multiply it by the indicated value of the vertical attenuation knob, and get the amplitude of the calibration signal;
(6) Read the number of grids occupied by each cycle of the waveform in the horizontal direction, multiply it by the indicated value of the horizontal scan knob, and get the period of the calibration signal (the inverse of the period is the frequency);
(7) The frequency of the general calibration signal is 1kHz and the amplitude is 0.5V, which is used to calibrate the internal scanning oscillator frequency of the oscilloscope. If it is abnormal, adjust the corresponding potentiometer of the oscilloscope (internal) until it matches.

2. Oscilloscope application example (taking the measurement of 13MHz clock pulse of 788 mobile phone as an example)
The normal 13MHz clock signal in the mobile phone is a necessary condition for turning on the phone, so it is necessary to frequently measure the presence of 13MHz clock signal during maintenance. The steps are as follows:
(1) Turn on the oscilloscope and adjust the brightness and focus knobs so that a horizontal bright line with moderate brightness and good focus is displayed on the screen;
(2) Calibrate the oscilloscope according to the above method, and then set the coupling mode to AC;
(3) Clamp the grounding clip of the oscilloscope probe to the grounding point of the mobile phone circuit board, and insert the probe into the 788 mobile phone CPU pin;
(4) Turn on the mobile phone power, press the power button, adjust the vertical scan level and the horizontal scan knob, and observe whether a stable waveform appears on the screen. If not, it generally means that there is no 13MHz signal.