Monday, August 20, 2018

LG CM4650 Mini Hi-Fi System SMPS and power amplifier schematic, repair procedure, hidden key modes and more


MODELS: LGCM4650, (LGCM4650, LGCMS4750F)
1) The pick-up incorporates a strong magnet, and so should never be brought close to magnetic materials.
2) The pick-up should always be handled correctly and carefully, taking care to avoid external pressure and impact. If it is subjected to strong pressure or impact, the result may be an operational malfunction and/or damage to the printed-circuit board.
3) Each and every pick-up is already individually adjusted to a high degree of precision, and for that reason the adjustment point and installation screws should absolutely never be touched.
4) Laser beams may damage the eyes.  Absolutely never permit laser beams to enter the eyes. NEVER switch ON the power to the laser output part (lens, etc.) of the pick-up if it is damaged.

If there is dust on the lens surface, the dust should be cleaned away by using an air bush (such as used for camera lens). The lens is held by a delicate spring. When cleaning the lens surface, therefore, a cotton swab should be used, taking care not to distort lens.
Never attempt to disassemble the pick-up.
Spring has excess pressure. If the lens is extremely dirty, apply isopropyl alcohol to the cotton swab.
(Do not use any other liquid cleaners, because they will damage the lens.) Take care not to use too much of this alcohol on the swab, and do not allow the alcohol to get inside the pick-up.  Before replacing a component part, first disconnect the power supply lead wire from the unit
2) All equipment, measuring instruments and tools must be grounded.
3) The workbench should be covered with a conductive sheet and grounded.
When removing the laser pick-up from its conductive bag, do not place the pick-up on the bag. (This is because there is the possibility of damage by static electricity.)
4) To prevent AC leakage, the metal part of the soldering iron should be grounded.
5) Workers should be grounded by an armband (1 M
W)
6) Care should be taken not to permit the laser pick-up to come in contact with clothing, in order to prevent static electricity changes in the clothing to escape from the armband.
7) The laser beam from the pick-up should NEVER be directly facing the eyes or bare skin.
Do not remove a replacement ESD device from its protective package until immediately before you are ready to install it. (Most replacement ESD devices are packaged with leads electrically shorted together by conductive foam, aluminum foil or comparable conductive materials).
7. Immediately before removing the protective material from the leads of a replacement ESD device, touch the protective material to the chassis or circuit assembly into which the device will by installed.
HIDDEN KEY MODE
Push both Front key and RCU key to activate it for 5 seconds.
1. Disc Lock On/Off (CD Function Only Active)
 Front Key : STOP
 RCU Key : STOP
2. Check Version and Option code
 Front Key : STOP
 RCU Key : PLAY/PAUSE
 You can change [Audio MCU Version <-> CD Controller Version <-> EEPROM Option] by SKIP+/-.
3. Clear EEPROM
 Front Key : STOP
 RCU Key : SKIP-
4. Edit EEPROM
 Front Key : STOP
RCU Key : SKIP+
 You can change the digit of option by SKIP+/-.
 You can edit 0~f by REPEAT or PLAY/PAUSE key.
5. Bluetooth DUT
 Front Key : STOP
 RCU Key : PROGRAM
 Bluetooth model only
6. Power Disc Lock On/Off (CD Function Only Active)
 Front Key : STOP
 RCU Key : EQ
7. Amp Clip On/Off
 Front Key : STOP
 RCU Key : Mute
Amp Clip Mode Change (Amp Clip On --> Amp Clip Off --> Level Down display)
SERVICE INFORMATION FOR EEPROM
POWER ON
FLD no disc status or AUX status
Remote control ‘Fwd skip’ + Front ‘STOP’ push same timing during 5 seconds
FLD ‘OP-0…
Move to appropriate position and make changes with remote control ‘skip, mode, play’ key
Press ENTER key
FLD ‘write ok
Remote control ‘Fwd skip’ + Front ‘STOP’ push same timing
FLD ‘E2P CLR
Completed.
Program download & update
MCS PROGRAM
Download program file name must be - HG520_FW_CM4750_DATE.bin
If security program (Water Wall) is activated on your PC, you must save the file to the USB storage device and disable the security software, then download the file to your set.
Caution: When downloading the file, you should neither unplug the USB device, change to the other function, nor power off the device. USB device must be unplugged when the downloading process is completed
On VFD display screen
EQ PROGRAM
Download program file name must be EQ_PRG_CM4750_***.BIN
If security program (Water Wall) is activated on your PC, you must save the file to the USB storage device and disable the security software, then download the file to your set.
Caution: When downloading the file, you should neither unplug the USB device, change to the other function, nor power off the device. USB device must be unplugged when the downloading process is completed
On VFD display screen
Repair help
NO POWER
If the unit doesn’t work by no power problem, repair the set according to the following guide.
FUSE & BRIDGE DIODE
check and replace F901, BD901, TH901 or TH903 on SMPS board.
How to troubleshoot (Countermeasure)
1) Check if the fuse F901 is open or short-circuit.
2) Check if the bridge diode BD901 is short-circuit by over current with a digital multi meter.
3) Check if the NTC thermistor TH901 or TH903 is normal or open.
If the unit doesn’t work by no power problem, repair the set according to the following guide.
D951
check and replace D951 on SMPS board.
How to troubleshoot (Countermeasure)
1) Check the anode-cathode voltage of D951 with a digital multi-meter, it is normally 0.2 ~ 0.3 V.   If it doesn’t have any voltage, it’s destroyed. Replace it with a new one.
NO BOOTING WHEN POWER ON THE SET
The set doesn’t work when press the power button on the front board or the remote control.
FLASH MEMORY
Check and replace IC503 on MAIN board.
How to troubleshoot (Countermeasure)
1) Check 5.6 V to CN501 in standby mode.   If there is no 5.6 V, check the SMPS.
2) Check 12 V, F+, F- and PVDD when power on the set.  - If the set doesn’t work regardless of what the KEY1 changes high to low while pressing the power button.
X500 and X501 work normally but, if you can not power on the set, replace IC501 with a new one on the MAIN board.
VFD is not displayed when power on the set
When power on the set, any icons or characters on VFD are not displayed.
check and replace DIG302 on FRONT board.
How to troubleshoot (Countermeasure)
1) Check if VKK, FL+ and FL- are output from SMPS to VFD via the MAIN board.
2) Check if IC501 outputs VFD_D0, VFD_CLK and VFD_STB to the FRONT board.
3) Check the GR signal (pulse signal) of IC408 on the FRONT board.
Check the SG signal (pulse signal) of IC408 on the FRONT board.
 If the GR and SG signal isn’t output, replace IC408 with a new one.  If the GR and SG signal is output, replace DIG302 with a new one.
NO OPERATION OF MD
When no sound output in the CD function, you can not listen to music reading data from a CD disc if the servo motors in MD don’t work. This step is for checking the SPINDLE MOTOR among them.
check and replace IC407, IC408 on MAIN board.
 How to troubleshoot (Countermeasure)
1) Check the SPDO signal from pin24 of IC407.  If no signal, check 3.3 V(RF) and X400.
2) Check the SPIN- & SPIN+ from IC408 to CN405 for driving SPINDLE motor. It is about 3.6 Vp-p. If no signal, check +1.8 V and +5 V for IC408.
3) Check if the FFC cable is solidly connected between CN405 and MD.
4) Check the MD. If the spindle motor is sort-circuit or has any trouble, it can not rotate CD discs.
check the function after changing another MD.
NO OPERATION OF MD
When no sound output in the CD function, you can not listen to music reading data from a CD disc if the servo motors in MD don’t work. This step is for checking the SLED MOTOR among them.
check and replace IC407, IC408 on MAIN board.
 How to troubleshoot (Countermeasure)
1) Check the SLDO signal from Pin23 of IC407.  If no signal, check 3.3 V(RF) and X400.
2) Check the SLED+ & SLED- from IC408 to CN405 for driving SPINDLE motor. It is about 2.9 Vp-p. If no signal, check +1.8 V and +5 V for IC408.
3) Check if the FFC cable is solidly connected between CN405 and MD.
4) Check the MD. If the sled motor is sort-circuit or has any trouble, it can not move the pickup module.
check the function after changing another MD
NO OPERATION OF MD
When no sound output in the CD function, you can not listen to music reading data from a CD disc if the servo motors in MD don’t work. This step is for checking the TRAY OPEN / CLOSE MOTOR among them.
 TRAY OPEN / CLOSE MOTOR
check and replace IC407, IC408 on MAIN board.
How to troubleshoot (Countermeasure)
1) Check MOT_OPEN & MOT_CLOSE signals from Pin K4, L4 of IC501 to IC408.  If no signal, check +1.8 V & + 5 V to IC408.
2) Check LOAD± from IC408 to CN405 for driving the tray open / close motor. It is about 3.85 Vp-p. If no signal, check +5 V to IC408. If it has any trouble, replace it with a new one.
3) Check if the FFC cable is solidly connected between CN405 and MD.
4) Check the MD.  If the tray motor is sort-circuit or has any trouble, it can not open or close the tray.
check the function after changing another MD.
NO OPERATION OF MD
When no sound output in the CD function, you can not listen to music reading data from a CD disc if the pickup module in MD doesn’t work. This step is for checking the LASER TRACKING ACTUATOR.
check and replace IC407, IC408 on MAIN board.
How to troubleshoot (Countermeasure)
The tracking actuator makes the laser beam be positioned in the center of a track on CD disc.
1) Check the TRD signal from Pin22 of IC407.  If no signal, check 3.3 V(RF) and X400.
2) Check TR- & TR+ from IC408 to CN408 for driving the tracking actuator.  If no signal, check +1.8 V and +5 V for IC408.
3) Check if the FFC cable is solidly connected between CN405 and MD.
4) Check the MD. If the pickup module has any trouble, it can not move the laser beam on the left or right side.
check the function after changing another MD.
NO OPERATION OF MD
When no sound output in the CD function, you can not listen to music reading data from a CD disc if the pickup module in MD doesn’t work. This step is for checking the LASER FOCUSING ACTUATOR.
check and replace IC407, IC408 on MAIN board.
How to troubleshoot (Countermeasure)
The focusing actuator makes the laser beam keep a regular interval with the surface of a CD disc.
1) Check the FOD signal from Pin21 of IC407.  If no signal, check 3.3 V(RF) and X400.
2) Check F- & F+ from IC408 to CN405 for driving the focusing actuator.  If no signal, check +1.8 V and +5 V for IC408.
3) Check if the FFC cable is solidly connected between CN405 and MD.
4) Check the MD. If the pickup module has any trouble, it can not move the laser beam on the top or bottom side.
check the function after changing another MD.
NO SOUND
There is no sound output in the CD FUNCTION, repair the set according to the following guide.
IN THE CD FUNCTION
check and replace IC501, IC601 on MAIN board.
How to troubleshoot (Countermeasure)
1) Check CD_BCLK, CD_LRCK, & CD_DOUTA signals from IC407 to IC501.  If no signal, check if the RF & servo signals from MD is entered to IC407.
Refer to the “No operation of MD” guide on Item 4.
2) Check the following I2S signal flow. < I2S audio signal Interface >
- DAC_BCK : IC501_Pin E1 --> IC601_Pin23
- DAC_LRCK : IC501_Pin D1 --> IC601_Pin22 (44.1 kHz)
- DAC_DATA : IC501_Pin E2 --> IC601_Pin24
- DAC_MCLK : IC501_Pin D2 --> IC401_Pin44
 If there is any trouble, check the power for each IC. The power is normal but, if the signal waveform to the IC is distorted or no signal, replace it with a new one.
3) check if “Digital audio AMP block” on Item 5-2 is normal.
NO SOUND
There is no sound output by DIGITAL AUDIO AMP DAMAGE, repair the set according to the following
BY DIGITAL AUDIO AMP DAMAGE (IN ALL FUNCTIONS)
check and replace IC701, IC702 on MAIN board.
How to troubleshoot (Countermeasure)
1) Check PWM_FL±, PWM_FR± & PWM_SW± signals from IC601 to IC701 & 702 each input function.  If no signal, check if I2S audio signals are entered to IC601.
Refer to “I2S audio signal interface” on Item 5-1.
2) Check PVDD. If PVDD is abnormal, check the SMPS.
3) Check +12 V for driving the gate of AMP IC.
a. All the powers are normal, but if +12 V is low, there is possible for AMP IC to be damaged.
b. Remove L701, L702, L703 and L704 one by one.
When removed a inductance, if +12 V is recovered, the IC connected to it was damaged.  c. Replace the IC with a new one.
4) Check the impedance between IC701/IC702_OUT_A/OUT_B & GND.
a. If the impedance is 0 Ω, the IC must be damaged.
b. After removing the heat sink, replace it with a new one.
NO SOUND
There is no sound output in the USB FUNCTION, repair the set according to the following
IN THE USB FUNCTION

Check and replace IC501 on MAIN board & IC302 on USB board.
How to troubleshoot (Countermeasure)
1) Check +5V_USB to USB board.  If the USB LED are turned on, the voltage is okay, if so not, check +5.6 V to pin6 of CN302.
2) Check USB D1± or USB D2± from MAIN board to USB board.
a. Check 2.0_D1±signals (pin U7, U8 ) or 1.1_D1± signals(pin A7, A8 ) to IC501.
b. Check USB± signals to CN302 (pin1, 2, 4, 5).  If there is any trouble, check the power for each IC. The power is normal but , if the signal waveform to
the IC is distorted or no signal, replace it with a new one.
3) check if “Digital audio AMP block” on item 5-2 is normal.
NO SOUND
There is no sound output in the AUX FUNCTION, repair the set according to the following
Check and replace IC201 on MAIN board.
How to troubleshoot (Countermeasure)
1) Check AUX_L/R signals to IC201 (Pin23, 24).
2) Check if MCS_BCK, MCS_LRCK & MCS_MCLK are entered from IC501 to IC201.
3) Check if ADC_DATA is entered from IC201 to IC501.  If no signal, check +5 V & +3.3 V(ADC) for IC201. If is NG, replace it a new one.
4) Check the following I2S signal flow from IC801 to IC602. If there is any trouble, check the power for each IC. The power is normal but, if the signal waveform to the IC is distorted or no signal, replace it with a new one.
5) Check if the digital audio AMP block is okay. If AMP is damaged, replace it with a new one.
There is no sound output in the TUNER FUNCTION, repair the set according to the following guide.
IN THE TUNER FUNCTION
check and replace IC201, TU500 on MAIN board.
How to troubleshoot (Countermeasure)
1) Check if TUNER_LR is entered from Pin1, 3 of TU500 to IC201(Pin26, 27).  If no signals, check +3.3 V for tuner power.
 Check if the tuner control signals (CLK, DAT, CE, RST, SLT) are entered from IC501 to TU500.
If it doesn’t work, replace TUNER with a new one.
2) Check if MCS_BCK, MCS_LRCK, & MCS_MCLK are entered from IC501 to IC201.
3) Check if ADC_DATA is entered from IC201 to IC501. If no signal, check +5 V & +3.3 V(ADC) for IC201. If is NG, replace it with a new one.
4) Check the following I2S audio signal flow from IC501 to IC601. If there is any trouble, check the power for each IC. The power is normal but, if the signal waveform to the IC is distorted or no signal, replace it with a new one.
5) Check if the digital audio AMP block is okay. If AMP is damaged, replace it with a new one.
NO SOUND
There is no sound output in the PORTABLE FUNCTION, repair the set according to the following guide.
IN THE PORTABLE FUNCTION
check and replace IC201 on MAIN board.
How to troubleshoot (Countermeasure)
1) Check PT_L/R signals to IC201 (Pin9, 10).
2) Check if MCS_BCK, MCS_LRCK, & MCS_MCLK are entered from IC501 to IC201.
3) Check if ADC_DATA is entered from IC201 to IC501. If no signal, check +5 V & +3.3 V(ADC) for IC201. If NG, replace it a new one.
4) Check the following I2S signal flow from IC501 to IC601. If there is any trouble, check the power for each IC. The power is normal but, if the signal waveform to the IC is distorted or no signal, replace it with a new one.
5) Check if the digital audio AMP block is okay. If AMP is damaged, replace it with a new one.
WAVEFORMS OF MAJOR CHECK POINTs
SMPS and Power amplifier schematic