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Play previously recorded TV programs, image and sound are good; After the re-recorded videotape television programs, the playback picture is normal, the sound muffled, turbid. The sound and the band sounds like a very slow speed when the tape recorder playing.mE2service manual download site
Generally, when the audio head is dirty, the playback sound of the impact is small, and has a great influence on the recording. From the failure phenomenon, the possibility of a larger audio head dirty, but after careful cleaning of the head, the fault remains.mE2service manual download site
mE2service manual download site
In the recording process, the VCR's audio and video output jack to the TV's were audio and video input jack connected to the TV picture, sound normal. Visible, VCR antenna receives RF signals by after-conversion tuner, demodulator output via the TV audio and video signals. According to the symptoms, recorded VCR audio circuits, put common part is working properly, the fault may occur in the recording amplifier, equalizer amplifier, audio signal control circuit, overlooking the magnetic oscillation circuit and other audio circuits.mE2service manual download site
To facilitate fault analysis, the following brief overview of the working principle of the VCR audio circuit.mE2service manual download site
NV-SD50MC audio recording circuit as shown.mE2service manual download site
Audio recording circuit mainly by the IC4001 (XRA7766AS) components. Audio signal is recorded directly into the line input jack JK3902 from the input and output circuit board via C3913 coupled to IC3902 (BA7604N) of ¢â feet, tuning into the input audio signal output circuit board through PS3902 ¢á foot strip through C3914 coupled to IC3902 The ¢à feet. The two-channel audio signals into IC3902, after input selection from ¢Þ output. Selection control signal output by the IC6710 16 through PP3005 ¢Þ-PS3901 ¢Þ-IC3902 ¢ß, the audio signal output line is high, the output tuning of the audio signal at the low level. Been recorded audio signal via C3915 coupling → PS3902 ¢à from the input and output circuit board output → PP3004 ¢à, into the main circuit board → IC4001 11 Enlarge → 14 output → C4033, C4001 coupling → two routes, all the way through PP4001 ¢à, go to karaoke oK circuit for EE signal output; another way through 20 magnify returns IC4001 → 24 → Output → C4008 plus bias magnetic coupling oscillation signal → P1501 ¢Ü send audio head record. In recording, the system control microprocessor IC6001 67 outputs a high level delay the audio recording via QR4001 inverted complementary low, then by IC4001 25 controls the switch 32 is turned off, the switch ¢Ü on the ground, constituting the recording magnetic head pathway. Bias magnetic oscillator mainly by Q4001, T4001 and feedback capacitor C4016 transformers and other components, which are controlled by IC4001 25 feet. When the VCR is recording, IC4001 25 goes low, the internal control signal IC4001 two transistors T1, T2 saturation: IC4001 28 and 27-pin connectivity, 27 feet to get 12V voltage, which is biased by L4002 magnetic oscillator operating voltage, bias magnetic oscillating electrical work. Bias magnetic bias magnetic signal generated by the oscillator output from the T4001 ¢Ü by VR. 4002 to adjust the audio signal superimposed with evacuations audio head record. Meanwhile, the bias magnetic oscillator also swung from T4001 ¢Ý pin output signal to sound erase head through P4001 ¢Ù, eliminate erase the original audio track.
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