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satellite receiver power supply board schematic explained
DVB-S receiver boot sequence step by step
A typical DVB-S/DVB-S2 satellite receiver consists of four major electronic sections:
Power supply board
LNB power and RF input section
Tuner/demodulator section
Main processor/SoC section
A simplified receiver architecture is:
Satellite Dish + LNB
|
| RF IF signal: 950–2150 MHz
| DC: 13/18 V
| 22 kHz tone / DiSEqC
v
+-------------------+
| F-connector input |
+---------+---------+
|
+--------------------+
| |
v v
RF coupling path LNB DC feed path
| |
v v
+----------------+ +---------------------+
| Tuner IC | | LNB power controller|
| RF downconverter| | 13/18 V + 22 kHz |
+--------+-------+ +----------+----------+
| ^
v |
+----------------+ |
| DVB-S/S2 |<----------------+
| demodulator | I2C control from SoC
+--------+-------+
|
| MPEG transport stream
v
+-----------------------------+
| Main SoC / CPU / AV decoder |
+-------------+---------------+
|
+--------+--------+-------------+
| | |
DDR RAM Flash HDMI/AVA DVB-S or DVB-S2 receiver does not receive the original Ku-band satellite carrier directly at the tuner IC. The satellite LNB mounted on the dish first converts the microwave satellite signal down to an intermediate frequency.
Typical Ku-band example:
Satellite RF: approximately 10.7–12.75 GHz
LNB local oscillator: usually 9.75 GHz or 10.6 GHz
Receiver input IF: approximately 950–2150 MHzThe receiver therefore processes the 950–2150 MHz L-band IF signal coming from the LNB.
A simplified RF/LNB input schematic looks like this:
To LNB through coax
|
F-CONN
|
+-------------------- RF path --------------------+
| |
| C_RF |
| 10 pF–100 pF|
| |
v v
Surge/ESD Tuner RF input
protection
|
|
GND
+-------------------- DC feed path ----------------+
|
L_RF choke
10 uH / RF choke
|
v
+----------------------+
| LNB power controller |
| 13/18 V, 22 kHz |
| DiSEqC capable |
+----------+-----------+
^
|
I2C/GPIO
|
Main SoCThis is the coaxial input from the satellite dish. It carries three things simultaneously:
| Signal | Purpose |
|---|---|
| 950–2150 MHz RF | Satellite IF signal from the LNB |
| 13 V or 18 V DC | Powers the LNB and selects polarization |
| 22 kHz tone | Selects low/high band and carries DiSEqC commands |
The tuner input must receive RF but must not receive the 13/18 V LNB voltage.
Therefore a small RF capacitor is placed in series with the RF path:
F-connector ---- C_RF ---- tuner inputThis capacitor passes high-frequency RF but blocks DC.
Typical values are in the range of:
10 pF to 100 pF, depending on tuner input designThe LNB supply voltage is injected onto the coaxial line through an RF choke:
LNB power IC ---- RF choke ---- F-connectorThe choke allows DC current to pass to the LNB but presents a high impedance to the 950–2150 MHz RF signal, preventing RF leakage into the power supply section.
Satellite coax cables can collect static charge and surge energy. Protection components are often placed near the F-connector:
F-connector ---- TVS diode / gas discharge tube / ESD diode ---- groundIn low-cost receivers, this protection may be minimal. In better designs, there may be:
The LNB power IC is one of the most important satellite-specific parts of the receiver. Example functions include:
Input: usually 12 V, 15 V, or 20 V
Output: 13 V or 18 V to coax
Control: I2C or GPIO from main processor
Protection: overcurrent, short-circuit, thermal shutdownTypical devices used in receivers include parts similar to:
| Output condition | Meaning |
|---|---|
| 13 V | Vertical polarization |
| 18 V | Horizontal polarization |
| 22 kHz off | Low band |
| 22 kHz on | High band |
| 22 kHz burst modulation | DiSEqC control |
For a universal Ku-band LNB:
Low band LO = 9.75 GHz
High band LO = 10.6 GHzThe receiver enables the 22 kHz tone when tuning high-band transponders.
A simplified tuner/demodulator chain is:
F-connector
|
RF protection and coupling
|
v
+----------------+
| RF tuner IC |
| LNA / mixer / |
| PLL / filters |
+-------+--------+
|
| I/Q baseband or low-IF
v
+----------------+
| DVB-S/S2 |
| demodulator |
| ADC + carrier |
| recovery + FEC |
+-------+--------+
|
| MPEG-TS
v
+----------------+
| Main SoC |
+----------------+The tuner selects a wanted carrier within the 950–2150 MHz input range. It usually contains:
The main SoC programs the tuner with:
The demodulator converts the selected modulated signal into a digital transport stream.
It performs:
Typical transport stream interface:
Parallel TS: D0–D7 + CLK + VALID + SYNC
or
Serial TS: DATA + CLK + VALID + SYNCIn newer receivers, tuner and demodulator may be integrated into one frontend IC or even partly integrated into the main SoC.
The main SoC is the central controller. It normally includes:
| Block | Function |
|---|---|
| CPU core | Runs bootloader, Linux/RTOS, application |
| DDR controller | External RAM interface |
| Flash interface | SPI NOR, NAND, or eMMC boot storage |
| DVB transport demux | Extracts audio/video/data PIDs |
| Video decoder | MPEG-2, H.264, H.265/HEVC depending on model |
| Audio decoder | MPEG audio, AAC, AC3 depending on license/model |
| HDMI transmitter | Digital audio/video output |
| CVBS DAC | Analog video output in older units |
| USB/Ethernet | Updates, media playback, networking |
| I2C/SPI/GPIO | Control of tuner, demodulator, LNB IC, display, IR |
A simplified SoC section:
+-------------------+
SPI NOR/NAND --->| |<---> DDR3/DDR4 RAM
| Main SoC |
Tuner/Demod ---->| |----> HDMI
Transport stream | |----> CVBS/Audio
| |<---- IR receiver
I2C/GPIO --------| |----> Front panel LEDs/display
+-------------------+Most set-top satellite receivers use a low-cost isolated flyback SMPS.
A typical schematic-level block diagram is:
AC mains
90–265 VAC
|
v
+--------+
| Fuse |
+--------+
|
v
+----------------+
| MOV / NTC / EMI|
| filter |
+----------------+
|
v
+----------------+
| Bridge rectifier|
+----------------+
|
v
+---------------------+
| Bulk capacitor |
| 400 V / 450 V |
+---------------------+
|
| high-voltage DC bus
v
+--------------------------+
| Flyback transformer |
| primary winding |
+------------+-------------+
|
v
+--------------------------+
| PWM controller + MOSFET |
| or integrated switcher |
+------------+-------------+
|
GND primary
Isolated secondary side
-----------------------
+------------------+ +------------------+
| 12 V rectifier |---->| tuner / LNB stage|
+------------------+ +------------------+
+------------------+ +------------------+
| 5 V rectifier |---->| USB / AV / logic |
+------------------+ +------------------+
+------------------+ +------------------+
| 3.3 V rectifier |---->| SoC / flash / IO |
+------------------+ +------------------+
Feedback:
3.3 V or 5 V rail ---> TL431 ---> optocoupler ---> PWM IC feedback pinThe primary side of this circuit is connected directly to the AC mains. The bulk capacitor can hold approximately:
160 VDC on 120 VAC mains
325 VDC on 230 VAC mainsand can remain charged after unplugging. Troubleshooting this section requires isolation, proper probes, discharge procedures, and experience with mains-powered equipment.
The fuse protects against catastrophic faults such as:
A blown fuse should never simply be replaced without identifying the fault.
The MOV clamps high-voltage mains transients.
Line ---- MOV ---- NeutralIf the unit was exposed to surge or lightning, the MOV may fail short and blow the fuse.
The NTC limits inrush current into the empty high-voltage bulk capacitor at power-on.
At turn-on:
NTC resistance = highAfter warming up:
NTC resistance = lowThe EMI filter prevents switching noise from returning to the mains.
It usually includes:
The bridge rectifier converts AC to high-voltage DC.
Approximate voltage:
\[ V{DC} \approx \sqrt{2} \times V{AC,RMS} \]
Examples:
\[ 120\,V{AC} \times 1.414 \approx 170\,V{DC} \]
\[ 230\,V{AC} \times 1.414 \approx 325\,V{DC} \]
The bulk capacitor smooths the rectified waveform and supplies the flyback converter.
The flyback converter stores energy in the transformer during the MOSFET on-time and transfers it to the secondary side during the MOSFET off-time.
Simplified switching operation:
MOSFET ON:
- Current ramps up in primary winding.
- Energy is stored in transformer magnetizing inductance.
- Secondary diodes are reverse-biased.
MOSFET OFF:
- Magnetic field collapses.
- Secondary diodes conduct.
- Energy charges output capacitors.Low-cost receivers often use ICs similar to:
The controller handles:
At first power-up, the PWM IC needs a small current to start. This is often supplied through a high-value resistor from the high-voltage bus:
HV DC bus ---- startup resistor ---- VCC pin of PWM ICOnce switching begins, an auxiliary transformer winding supplies VCC more efficiently:
Aux winding ---- diode ---- capacitor ---- PWM IC VCCCommon fault:
Receiver clicks or pulses but does not startPossible cause:
The primary winding leakage inductance produces a high-voltage spike when the MOSFET turns off. A snubber protects the MOSFET.
Common snubber:
RCD clamp = resistor + capacitor + fast diodeFaults in this section can destroy the MOSFET or integrated switcher.
Typical satellite receiver rails:
| Rail | Common use |
|---|---|
| 12 V | Tuner, LNB supply input, AV circuits |
| 5 V | USB, HDMI, front panel, regulators |
| 3.3 V | Flash, logic, tuner/demod I/O |
| 1.8 V | DDR, tuner/demod core, SoC I/O |
| 1.5 V / 1.35 V | DDR3/DDR3L memory |
| 1.0–1.2 V | SoC core voltage |
The main SMPS may only provide 12 V, 5 V, and 3.3 V. Smaller buck regulators or LDOs on the mainboard then generate:
1.2 V core
1.5 V DDR
1.8 V logicThe output voltage is regulated through an isolated feedback loop.
Simplified feedback schematic:
Secondary side Primary side
+5 V or +3.3 V
|
R1
|
+---- TL431 REF
|
R2
|
GND
TL431 cathode ---- optocoupler LED ---- resistor ---- output rail
Optocoupler transistor ---- PWM feedback pinIf the output voltage rises:
TL431 conducts more current
Optocoupler LED becomes brighter
Primary feedback signal increases
PWM duty cycle decreases
Output voltage fallsIf the output voltage falls:
TL431 conducts less current
Optocoupler LED becomes dimmer
PWM duty cycle increases
Output voltage risesThe regulated rail is usually the 5 V or 3.3 V rail. Other rails are cross-regulated by transformer winding ratios and load conditions.
A typical DVB-S receiver boot sequence is as follows.
The SMPS starts and generates standby or main rails.
AC input → SMPS → 5 V standby / 3.3 V / 12 VSome receivers have a standby microcontroller or front-panel controller powered first. Others power the full SoC immediately.
On the mainboard, DC-DC converters generate low-voltage rails:
12 V → LNB controller / tuner supply
5 V → USB / HDMI / regulators
3.3 V → flash / logic / I/O
1.8 V → tuner/demod / DDR I/O
1.5 V → DDR3
1.1 V → SoC coreThe reset supervisor holds the SoC in reset until voltages are valid.
When rails are stable:
RESET_N goes high
SoC begins executionThe CPU starts from an internal boot ROM address.
The SoC’s mask ROM performs basic initialization:
The first-stage bootloader, sometimes called SPL, initializes hardware that the internal ROM cannot fully configure.
It usually performs:
DDR initialization is a critical point. If the unit hangs here, possible causes include:
The second-stage bootloader may be U-Boot, CFE, or a proprietary bootloader.
It performs:
Common boot messages may include:
U-Boot
DRAM: 256 MiB
NAND: ...
SPI Flash: ...
Loading kernel...
Starting kernel...If the receiver is stuck on “BOOT”, the failure may occur at this stage or during early kernel startup.
For Linux-based receivers, the kernel then:
For RTOS-based receivers, a monolithic firmware image may initialize drivers directly without a full Linux-style boot process.
The first user-space process starts:
/sbin/init
systemd
busybox init
proprietary init systemThen the receiver application or middleware starts.
Examples of application-level tasks:
When the receiver tunes a channel, software calculates the required LNB and tuner settings.
Example:
Wanted satellite transponder: 11.836 GHz horizontal high band
LNB high-band LO: 10.6 GHz
Receiver IF = 11.836 GHz - 10.6 GHz = 1.236 GHzThe receiver then sets:
LNB voltage = 18 V for horizontal
22 kHz tone = ON for high band
Tuner frequency = 1236 MHz
Symbol rate = transponder symbol rate
Demodulation = DVB-S or DVB-S2
FEC = auto or specifiedThe demodulator searches for and locks to the carrier.
It reports status bits such as:
Signal present
Carrier lock
Viterbi/LDPC lock
Sync lock
Transport stream validIf lock is successful, an MPEG transport stream flows into the SoC.
The SoC demultiplexer extracts selected PIDs:
Video PID
Audio PID
PCR PID
Subtitle PID
ECM/EMM PIDs for encrypted servicesThen:
Likely section:
Primary SMPS or standby supplyCheck:
Expected measurements:
| Test point | Approximate value |
|---|---|
| Bulk capacitor on 120 VAC mains | 150–170 VDC |
| Bulk capacitor on 230 VAC mains | 300–330 VDC |
| 5 V rail | 5.0 V |
| 3.3 V rail | 3.3 V |
| 12 V rail | 11.5–12.5 V |
Use proper isolation and safety procedures.
Likely causes:
Best diagnostic method:
Connect USB-to-TTL UART adapter to the receiver mainboard service header.Typical UART levels are 3.3 V TTL, not RS-232 voltage levels.
Look for logs such as:
DDR init failed
Bad CRC
Bad magic number
Kernel panic
Unable to mount root fs
NAND read errorLikely causes:
Check at the F-connector:
| Condition | Expected voltage |
|---|---|
| Vertical channel | approximately 13 V |
| Horizontal channel | approximately 18 V |
| Receiver standby | often 0 V, depending on model |
| High-band channel | 22 kHz tone present |
Use a multimeter for DC voltage and an oscilloscope or satellite meter for the 22 kHz tone.
Most likely:
22 kHz tone missingPossible causes:
Most likely:
18 V LNB supply problemPossible causes:
Likely causes:
Check with oscilloscope:
12 V rail ripple
5 V rail ripple
3.3 V rail ripple
SoC core rail stabilityHigh ESR capacitors are a very common failure in older receivers.
This is not a manufacturer-specific schematic, but it represents the common topology used in many receivers:
AC INPUT
L o----FUSE----NTC----+----+------------------+
| | |
MOV EMI BRIDGE
| FILTER RECTIFIER
N o-------------------+----+------------------+
|
+---- +HV DC
|
C_BULK
22–68 uF
400/450 V
|
GND_PRI
+HV DC
|
|
Primary winding
|
+------ Drain
+----------------+
| PWM/MOSFET IC |
+----------------+
|
Source
|
GND_PRI
Aux winding ---- diode ---- C_VCC ---- VCC of PWM IC
Secondary winding 1 ---- Schottky ---- LC filter ---- +12 V
Secondary winding 2 ---- Schottky ---- LC filter ---- +5 V
Secondary winding 3 ---- Schottky ---- LC filter ---- +3.3 V
+5 V or +3.3 V ---- resistor divider ---- TL431
|
v
Optocoupler LED
|
Optocoupler transistor
|
PWM feedback pin Coax to dish/LNB
|
F-CONN
|
+-------------+-------------+
| |
| |
C_RF L_CHOKE
DC block RF choke
| |
v v
Tuner RF input LNB output pin
of LNB power IC
|
+----------+----------+
| LNB controller IC |
| 13/18 V generator |
| 22 kHz tone |
| DiSEqC |
| current protection |
+----------+----------+
|
12 V / 15 V input
|
control via I2C/GPIO
|
SoCUseful board test points include:
| Test point | What to expect |
|---|---|
| Bulk capacitor | 150–170 VDC on 120 VAC, 300–330 VDC on 230 VAC |
| PWM IC VCC | Often 10–18 V depending on IC |
| 12 V rail | Stable 11.5–12.5 V |
| 5 V rail | Stable 4.85–5.15 V |
| 3.3 V rail | Stable 3.2–3.4 V |
| SoC core rail | Often 0.9–1.2 V |
| DDR rail | 1.35 V, 1.5 V, or 1.8 V depending on RAM |
| F-connector vertical | Around 13 V |
| F-connector horizontal | Around 18 V |
| 22 kHz tone | Present for high band or DiSEqC commands |
| UART TX pin | Boot log at 3.3 V TTL level |
Modern DVB-S2/S2X receivers are increasingly integrated compared with older DVB-S units.
Important trends include:
For repair work, the trend toward BGA SoCs, integrated tuner modules, and secure firmware makes component-level repair harder than on older discrete designs.
When analyzing a receiver board, separate it into these functional areas:
1. AC input and SMPS primary
2. SMPS secondary outputs
3. Mainboard regulators
4. SoC, DDR, flash
5. RF tuner/demodulator
6. LNB power circuit
7. HDMI/AV/front panel/IR/USBDo not try to understand the whole board at once. Follow the power first, then the control buses, then the signal path.
Recommended sequence:
Use UART first. It gives the most information with the least board disturbance.
Typical UART settings:
Voltage: 3.3 V TTL
Baud rate: often 115200 bps
Data: 8 bits
Parity: none
Stop bits: 1Do not connect an old ±12 V RS-232 serial port directly to the board. Use a USB-to-TTL adapter.
At the F-connector:
Vertical transponder → approximately 13 V
Horizontal transponder → approximately 18 V
High band → 22 kHz tone present
Low band → 22 kHz tone absentIf the voltage collapses when the coax is connected, suspect:
A satellite receiver takes a 950–2150 MHz IF signal from the LNB, powers and controls that LNB using 13/18 V plus a 22 kHz tone, tunes and demodulates the DVB-S/S2 signal, then decodes the transport stream using the main SoC. The power supply is usually an isolated flyback SMPS producing 12 V, 5 V, and 3.3 V rails, with local regulators generating lower SoC and DDR voltages. During boot, the receiver progresses through power stabilization, reset release, ROM bootloader, secondary bootloader, kernel or RTOS startup, driver initialization, application loading, LNB/tuner setup, demodulator lock, and finally audio/video playback.