JPS6017990Y2 - noise detection device - Google Patents

Description

[Detailed Description of the Invention] The present invention is designed to detect defects in the printed circuit board when the printed circuit board is defective during the inspection process of the printed circuit board that constitutes the required television receiver circuit.
The present invention relates to a noise detection device that can detect noise superimposed on a video signal of a constant brightness level for testing.

When inspecting a printed circuit board that constitutes the video circuit of a television receiver, a video signal of a constant brightness level obtained from the circuit of this printed circuit board is added to the noise detection device that constitutes the inspection device, and the printed circuit board is inspected. give vibration to,
If the printed circuit board is defective (soldering defect, etc.), it is twisted and superimposed on the video signal, and by detecting the presence or absence of this noise, it is possible to determine whether the printed circuit board is good or defective.

The present invention is intended to provide a noise detection device that can efficiently detect defects in circuit components in such inspection devices.

One embodiment will be described below with reference to the accompanying drawings.

In FIG. 1, reference numeral 1 denotes an input terminal of a buffer circuit 2, to which a test video signal of a constant brightness level called a flat field video signal is applied.

Here, if the printed circuit board constituting the video circuit is defective, either or both of high frequency noise X and low frequency noise Y will be superimposed on the video signal and output as shown in FIG. Added to terminal 1.

This buffer circuit 2 has an amplification factor of 1 and operates as a high impedance manual buffer so that the input signal level is not affected.

4 is an analog switch, which is closed when the blanking signal (Fig. 2B) which is a mixture of the horizontal blanking signal and the vertical blanking signal applied to the input terminal 3 is at a high level, and is opened when it is at a low level. It is configured like this.

The output signal of the buffer circuit 2 is charged in the capacitor 5 when the analog switch 4 is in the closed state.

This capacitor 5 has a capacitance value that is sufficient as the output impedance of the buffer circuit 2 and the capacitance of the time constant circuit composed of the capacitor 5 so that it can sufficiently track the noise component superimposed on the video signal, and has a small leakage current. use.

During the period when the analog switch 4 is open, the voltage charged in the capacitor 5 is held and the synchronizing signal component of the video signal is removed.

The capacitor 5 and the analog switch 4 are connected to a high impedance buffer circuit 6 having a time constant so large that the amount by which the voltage charged in the capacitor 5 is discharged can be ignored.

For this reason, the initialization of the video signal is removed from the output of the buffer circuit 6, and a video component (FIG. 2C) containing a DC component appears.

A capacitor 7 connected to the output terminal of the buffer circuit 6
and a resistor 8, the DC component of the output of the buffer circuit 6 is removed, and only the AC component is applied to the positive terminal of the positive level comparator 9 and the negative terminal of the negative level comparator 10.

A variable resistor 13 to which a +■ voltage is applied is connected to the negative terminal of the positive level comparator 9, and when a voltage equal to or higher than the voltage +Vs set by the variable resistor 13 arrives, a pulse signal ( It appears as Figure 2D).

Also, the positive terminal of the negative side level comparator 10 has one
A variable resistor 14 to which a voltage is applied is connected, and when a voltage lower than the voltage -Vs set by the variable resistor 14 arrives, it appears at the output terminal 12 as a pulse signal (FIG. 2E).

In this way, the synchronization signal component can be removed and the noise components can be detected separately into positive and negative components.

Therefore, for example, if a video signal of a constant brightness level obtained from a circuit of a printed circuit board that constitutes the video circuit of a television receiver is applied to terminal 1, and vibration is applied to this printed circuit board, the pudding! - If there is a soldering defect on the board or a contact part of the lead, it becomes noise and is superimposed on the above video signal.

This noise is detected at terminals 11.12, and both terminals 11.1
If an output is output from at least one of the two, it can be determined that the printed circuit board is defective, and inspection efficiency is greatly improved.

As described above, according to the present invention, it is possible to efficiently detect a defect in a circuit component formed on a printed circuit board by removing the synchronizing signal component from a television signal and detecting only noise.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a noise detection device according to an embodiment of the present invention, and FIGS. 2A, B, C, D, and E are operational waveform diagrams of the same device. 1.3...Input terminal, 2,6...Buffer circuit, 5...Capacitor, 7...
Capacitor, 8... Resistor, 9... Positive side level comparator, 10... Negative side level comparator, 11.12... Output terminal, 13, 1
4...Variable resistor.

Claims (1)

[Scope of utility model registration request] For an input video signal with a constant brightness level including a synchronization signal,
means for removing the blanking period to keep the DC level of the video signal constant; means for extracting only the AC component, which is noise, from the video signal and converting it into a pulse component; and a comparison means for representing an output.