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Details power sources, consumption, and adapter compatibility.
Lists supported radio bands and antenna types.
Explains the operation and components of the built-in timer.
Procedures for tuning FM section IF and tracking.
Fine-tuning FM bands for accurate reception.
Procedures for tuning AM section IF and tracking.
Fine-tuning AM bands for accurate reception.
Setting and calibrating the timer function for operation.
Detailed steps for verifying timer calibration accuracy.
Details power sources, consumption, and adapter compatibility.
Lists supported radio bands and antenna types.
Explains the operation and components of the built-in timer.
Procedures for tuning FM section IF and tracking.
Fine-tuning FM bands for accurate reception.
Procedures for tuning AM section IF and tracking.
Fine-tuning AM bands for accurate reception.
Setting and calibrating the timer function for operation.
Detailed steps for verifying timer calibration accuracy.
The Sony ICF-7800 is a versatile FM/AM 3-band receiver designed for a wide range of listening experiences, offering both portability and robust functionality. Its primary function is to receive radio broadcasts across the FM, SW (Shortwave), and MW (Medium Wave) bands, providing users with access to local and international programming.
The ICF-7800 operates as a superheterodyne receiver, a common and effective architecture for radio reception. This design involves converting incoming radio frequencies to a fixed intermediate frequency (IF) for amplification and processing, which helps in achieving good selectivity and sensitivity.
For FM reception, the device utilizes an FM RF amplifier (Q1) and an FM converter (IC1) to process signals from the telescopic antenna. The FM IF amplifier (IC2, IC3, IC4) further amplifies these signals before they are demodulated by the FM detector (D6, D7). An Automatic Frequency Control (AFC) circuit (S4-1) can be engaged to stabilize FM tuning, reducing drift and improving reception quality, especially in areas with weak signals.
For AM (MW and SW) reception, the device employs an AM RF amplifier (Q2) and an AM converter (IC5). MW signals are picked up by a built-in ferrite-rod antenna, while SW signals, like FM, use the telescopic antenna. The AM IF amplifier (IC4) processes these signals, which are then demodulated by the AM detector (D5). An Automatic Gain Control (AGC) circuit is integrated to maintain a consistent output volume despite variations in signal strength. This AGC system operates in two stages: a reverse AGC in IC4 and a shunt AGC for Q2, ensuring stable audio output.
The audio output from both FM and AM sections is fed into a preamplifier (IC7) and then to a tone control amplifier, which allows users to adjust the sound characteristics. The tone control is of an NF (Negative Feedback) type, where the volume setting influences the emphasis of bass and treble. At lower volume settings, bass and treble emphasis are more pronounced, creating a "loudness" effect. The VR1 (BASS) control adjusts low frequencies, while VR2 (TREBLE) controls high frequencies. The VR3 (VOLUME) control not only adjusts the overall output level but also influences the effect of the tone controls. Finally, the amplified audio is delivered to the speaker (SP) via a power amplifier (IC6). The power amplifier utilizes a BTL (Balanced Transformer-less) circuit, which is capable of producing a large output from a small-sized amplifier, enhancing the listening experience.
A unique feature of the ICF-7800 is its electronic timer, which is integrated into a single IC (IC8). This timer includes a blocking oscillator, a counter, a digital-analog (DA) converter, a comparator, a switching circuit, a remaining-duration-time detector, a voltage regulator, and a current detector. The timer allows the user to preset the radio to automatically switch ON or OFF at a specified time. The timer selector (S2-1) can be set for either 96 minutes or 8 hours, changing the oscillation frequency of the internal oscillator. The remaining duration time can be indicated on the meter (ME).
The ICF-7800 is designed for flexible power options, making it suitable for both portable and home use. It can be powered by four AA-sized batteries for on-the-go listening. For stationary use, it supports AC power through optional AC adaptors and chargers, with different models available for UK, AEP, and E regions, accommodating various voltage and frequency standards (110V, 220V, 240V AC at 50/60 Hz). An optional 12V car battery cord (DCC-127H) further extends its portability to vehicles.
The device features multiple output jacks: an earphone minijack for private listening, a recording minijack for connecting to an external recording device, and an MPX OUT minijack, likely for connecting to an external stereo decoder or other audio equipment.
The front panel includes intuitive controls for tuning, volume, and tone (bass and treble). A band select switch (S1) allows easy switching between FM, SW, and MW bands. The AFC switch (S4-1) provides an option to stabilize FM reception. The timer select switch (S2) allows users to set the timer for different durations or turn it off, while the power switch (S3) controls the main power. A meter select switch (S5) allows the meter to display tuning information.
The service manual provides detailed instructions for disassembly and reassembly, facilitating maintenance and repair. Key components like the rear case, chassis (dial and speaker sections), timer board, switch board, and main board can be systematically removed and replaced.
For optimal performance, the manual outlines specific adjustment procedures for the FM, AM, and timer sections. These adjustments are crucial after replacing components or if the receiver's performance degrades.
The manual also includes a comprehensive electrical parts list and hardware nomenclature, aiding technicians in identifying and sourcing replacement components. This level of detail ensures that the ICF-7800 can be effectively serviced and maintained, extending its lifespan and ensuring continued high-quality performance.
General| Tuning System | Analog |
|---|---|
| FM Frequency Range | 87.5 - 108 MHz |
| Battery Type | 4 x AA |
| Headphone Jack | Yes |
| Bands | FM, SW |
| SW Frequency Range | 3.9 MHz |
| Power Source | AC and Battery |
| Speaker | Built-in |
| Antenna | Telescopic |
