KR940003434Y1 - Head contamination detecting circuit - Google Patents

Abstract

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Description

Detecting whether there is any foreign matter in the video head by sound

1 is a conventional circuit diagram.

2 is a video head foreign matter contamination detection circuit according to the present invention.

* Explanation of symbols for main parts of the drawings

10: microcomputer 20: audio signal processing unit

30: envelope detection unit D ₁ ~ D ₆ : diode

Q ₁ to Q ₅ : Transistors R ₁ to R ₄ : Resistance

In the VTR, when the video signal is not reproduced on the monitor in the tape playback mode, the sound of the VTR can determine whether the video head is contaminated by foreign matter or the video signal processing itself is abnormal. The present invention relates to a circuit for detecting foreign matter contamination of the video head by the presence or absence of sound.

As is well known, in a VTR, a video signal input from a TV tuner and a video camera or other video is modulated into an FM waveform and recorded and reproduced in a video head.

In this case, the signal read from the video head is called an envelope signal, which is FM demodulated and then output through a monitor.

In the related art, as shown in FIG. 1, the microcomputer mute terminal 1 and the synchronization signal terminal 2 of the microcomputer (not shown) are connected to the audio signal processor 3 through the diodes D ₁ and D ₂ . It is connected to the audio mute terminal (3 '), so when operating in cue mode, review mode, still mode or slow mode, that is, in special playback mode, If the "high" level signal is output in 1) and the video is not played back on the monitor in the tape playback mode of the VTR, that is, if there is no video signal, the "high" level signal is output from the SYNC (L) terminal and the audio signal processor By applying to (3), the voice is forcibly muted.

In this way, if there is no video signal, the audio bar is automatically muted by the control of the microcomputer. Therefore, it is impossible to determine whether the video head is muted by a foreign material or whether the video head is muted due to an abnormality of the video signal processing circuit itself. You'll have a hard time confirming the odds.

The present invention has been made to solve the above problems. If the video head is contaminated by foreign matter in the tape playback mode, the audio is muted and the video signal is not played back due to an abnormality in the video circuit or other malfunction. The audio is not operated as a mute so that it can be judged by the presence or absence of audio sound.

This will be described in detail with reference to the accompanying drawings.

In the known one consisting of the microcomputer 10 and the audio signal processing unit 20, the anode of the resistor R ₁ and the diodes D ₃ and D ₄ are connected in parallel to the base of the emitter grounded transistor Q ₁ . The cathodes of diodes D ₃ and D _{4 are} connected to the EE (H) and sync (L) terminals of the microcomputer 10, respectively, and the collectors of transistor Q ₁ are connected to the resistors R ₂ and Q _2. ) diode (D ₅ and connected to the base, emitter, but connected to the anode of a collector and a diode (D _5, D ₆₎ of the base of the grounding transistor (Q _4), an emitter grounded transistor (Q ₃₎ in parallel with the , The cathode of D ₆ ) is connected to the sync (L) and EE (L) terminals, respectively, and the collector of transistor (Q ₄ ) is connected in parallel to the emitter of resistor (R ₃ ) and transistor (Q ₅ ). , connected to an envelope detector 30 to the emitter of the transistor (Q ₃₎ and transistors (Q _2, Q _3), the collector of the audio signal processor 20 of the O O is the hayeoseo connected to the mute terminal (A).

When explaining the effect of the present invention made as follows.

In the output terminal of the general microcomputer 10, in the EE mode and the record mode, the EE (H) is in the "high" level state, and the EE (L) is in the "low" level state. EE (H) enters the "low" level state and EE (L) operates in the "high" level state.

First, in the EE mode and the record mode, when there is a video signal, the SYNC (L) terminal of the microcomputer 10 is in the "low" level state, so that the transistors Q ₁ and Q ₄ are turned off. As a result, the transistors Q ₂ and Q ₅ are also “turned off” so that the power supply Vcc is not supplied to the audio mute terminal A of the audio signal processor 20, and thus, the audio mute is not operated.

However, when there is no video signal, the sync signal is also not due to SYNC (L) of the microcomputer terminal is the "High" level state EE (H) terminal is also because the "high" state, the transistor (Q ₁₎ is being "turned on" The Accordingly, the transistor Q ₂ is also "turned on" to supply a power supply Vcc to the audio mute terminal A of the audio signal processor 20 to operate as an audio mute.

On the other hand, in the playback mode, when the envelope signal is detected in the video head but there is no video signal due to an abnormality in the video circuit or other failure, the EE (L) terminal of the microcomputer is in the "high" level state and the video signal. Since the SYNC (L) terminal is also in a "high" level, the envelope signal detected by the video head "turns on" transistor Q ₃ , which causes transistors Q ₄ and Q ₅ to "turn off". Since the power supply Vcc is not provided to the audio mute terminal A of the audio signal processor 20, the audio mute terminal A does not operate as an audio mute.

However, if the audio head is contaminated by a foreign substance, the envelope signal is not detected and therefore the video signal is not output. In this case, the microcomputer's EE (L) terminal becomes high level and there is no video signal. The transistor Q ₃ is " turned off " because of the " level state " and there is no voltage output from the envelope detector 30, thereby the transistors Q ₄ and Q ₅ are " turned on " A power supply Vcc is provided to the audio mute terminal A to operate as an audio mute.

In other words, if there is no video signal in EE mode and record mode, the audio is muted. If there is video signal, audio muting is disabled. In playback mode, audio mute operation is not performed according to the envelope detection signal even if there is no video signal. It is distinguished.

In this way, the present invention is designed to prevent audio muting if the video head is contaminated by foreign matter in the tape play mode of the VTR, and to disable the audio mute when an abnormality or other malfunction occurs in the video circuit. It is provided to determine whether there is sound pollution or foreign matter contamination or abnormality of the image signal processing circuit.

Claims (1)

In the known one consisting of the microcomputer 10 and the audio signal processing unit 20, the anodes of the resistors R ₁ and the diodes D ₃ and D ₄ are connected in parallel to the base of the emitter grounded transistor Q ₁ . The cathodes of the diodes D ₃ and D _{4 are} connected to the EE (H) and SYNC (L) terminals of the microcomputer 10, respectively, and the collectors of the transistors Q ₁ are connected to the resistors R ₂ and Q _2. ) of and connected to the base, emitter, but open the anode collector and a diode (D _5, D ₆₎ of the base of the grounding transistor (Q _4), an emitter grounded transistor (Q _3), the diode (D _5, D connecting the cathode of ₆₎ to each SYNC (L) terminals and EE (L) terminals and the resistance (R ₃₎ mid transistor (Q ₃ between the emitter of the transistor (Q _4), the collector and the transistor (Q ₅₎ of a) And the collector of the transistors Q ₂ and Q ₅ to the audio mute terminal A of the audio signal processor 20. Video head foreign matter contamination detection circuit with and without sound.