LG TH900 User manual

3-2
ONE POINT REPAIR GUIDE
1. NO POWER
If the unit doesn’t work by no power problem, repair the set according to the following guide.
1-1. FUSE/ THERMISTOR/ BRIDGE DIODE
1-1-1. Solution
Please check and replace F901, TH901 or TH903, BD901 on SMPS board.
1-1-2. How to troubleshoot (Countermeasure)
1) Check if the fuse F901 is open or short-circuit.
2) Check if the NTC thermistor TH900 or TH903 is normal or open.
3) Check if the bridge diode BD901 is short-circuit by over current with a digital multi-meter.
1-1-3. Service hint (Any picture/ Remark)
< F901 >
If F901 is not short-circuit,
replace it with a same
specifications one.
< BD901 >
If BD901 is short-circuit,
replace it with a new one.
<TH901 or TH903 >
If TH901 or TH903 is open,
replace it with a new one.
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3-3
ONE POINT REPAIR GUIDE
NO POWER
If the unit doesn’t work by no PVDD problem, repair the set according to the following guide.
1-2. FUSE/ FET
1-2-1. Solution
Please check and replace F901, Q901 on SMPS board.
1-2-2. How to troubleshoot (Countermeasure)
1) Check if the fuse F901 is open or short-circuit.
2) Check the anode-cathod 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.
1-2-3. Service hint (Any picture/ Remark)
< SMPS circuit >
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3-4
ONE POINT REPAIR GUIDE
2. NO BOOTING WHEN POWER ON THE SET
The set doesn’t work when press the power button on the top board or the remote control.
2-1. IC501
2-1-1. Solution
Replace IC501 on MAIN board.
2-1-2. How to troubleshoot (Countermeasure)
1) Check the +12 VA (CN202) and 3.3VA (IC503) in standby mode.
 If there is no 12 VA, check the SMPS and if doesn’t appear 3.3 VA, check IC503.
2) Check +12 VA, +5.1 VA, 3.3 VA, DVCC_5V and DVCC_3.3V 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 the IC501 with a new one
on the main board.
2-1-3. Service hint (Any picture/ Remark)
< MAIN board top view >
< MAIN board bottom view >
X500
X500
(24 MHz)
(24 MHz)
X501
X501
(32.768 kHz)
(32.768 kHz)
KEY1
KEY1
(R518)
(R518)
PWR_CTRL
PWR_CTRL
R559
R559
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3-5
ONE POINT REPAIR GUIDE
3. VFD IS NOT DISPLAYED WHEN POWER ON THE SET
When power on the set, any icons or characters on VFD are not displayed.
3-1. VFD (VFD301)
3-1-1. Solution
Please check and replace VFD301 on TOP FRONT board.
3-1-2. How to troubleshoot (Countermeasure)
1) Check if VFD_12V, DVCC_3.3V and VCC_5V are output from SMPS to VFD via the main board.
2) Check if the IC501 outputs VFD_CLK, VFD_STB, and VFD_DAT to the top board.
3) Check if the VFD grid current amplifier circuit on the top board.
Check the drive signal to the transistor’s(Q801,2) base.
 If the control signals from VFD (DGND, VDD) isn’t output, replace VFD with a new one.
3-1-3. Service hint (Any picture/ Remark)
R812(TP 841)
Q801 Emitter
about
30 Vp-p
< TOP FRONT circuit >
< Waveform of the grid current driver>
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3-6
ONE POINT REPAIR GUIDE
4. NO BOOTING (IN CD/USB FUNCTION)
After you turn on power key and displayed message in the following order (HELLO VOL XX 
CD or USB) on VFD, it will not display other message on VFD, and it will not boot-up normally.
4-1. NO DVCC_3.3V, 1.2 VA
4-1-1. Solution
Please check and replace IC202, IC205 on MAIN board.
4-1-2. How to troubleshoot (Countermeasure)
1) Check Voltage of IC202 pin3 on MAIN board.
 If IC202 pin3 (about 5.1 V) & pin1 Input 12 VA doesn’t come out, check +12 VA from SMPS board.
2) If IC202 pin3 (about 5.1 V) is normal, check voltage of IC205 pin3 (about 1.2 VA), pin6 (about 3.3 VA).
If IC205 pin3 (about 1.2 VA), pin6 (about 3.3 VA) doesn’t come out, check R253, R254, R256 and R260, R261, R262.
If there’s no defective component then replace IC205.
3) PWR_CTRL is high, check R512 and if there’s no defective component then replace IC505.
PWR_CTRL (IC505 pin3) is high (about 3.2 V)
 If PWR_CTRL isn’t high, check pin D11 of IC501 & R512, R513
4) If PWR_CTRL is high, check R559 and if there’s no defective component then replace IC505.
4-1-3. Service hint (Any picture/ Remark)
< MAIN board top view >
< MAIN board bottom view >
IC505
IC505
IC202
IC202
IC205
IC205
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3-7
ONE POINT REPAIR GUIDE
NO BOOTING (IN CD/USB FUNCTION)
After you turn on power key and displayed message in the following order (HELLO VOL XX 
CD or USB) on VFD, it will not display other message on VFD, and it will not boot-up normally.
4-2. CRYSTAL (X500)
4-2-1. Solution
Replace X500 on MAIN board.
4-2-2. How to troubleshoot (Countermeasure)
1) If 3.3 VA & 1.2 VA is normal, check reset ‘High’ of IC501 pin T12 on MAIN board.
 If MAIN_RESET isn’t high, check MICOM (IC101) pin40.
2) If MAIN_RESET is high, check the soldering status of 24 MHz crystal (X500).
3) If the crystal (X500) doesn’t oscillate, check R508, C502, C503 around crystal (X500).
 If there’s no defective component, then replace X500.
4-2-3. Service hint (Any picture/ Remark)
X
XI
XO
X500
< Signal waveform >
< MAIN board top view >
IC501
IC501
X500
X500
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3-8
ONE POINT REPAIR GUIDE
NO BOOTING (IN CD/USB FUNCTION)
After you turn on power key and displayed message in the following order (HELLO VOL XX 
CD or USB) on VFD, it will not display other message on VFD, and it will not boot-up normally.
4-3. SERIAL FLASH (IC503)
4-3-1. Solution
Please check and replace IC503 on MAIN board.
4-3-2. How to troubleshoot (Countermeasure)
1) If the crystal (X500) does oscillate, check serial flash (IC503) on MAIN board.
 Check pin8 (VCC), pin6 (CLK), pin1 (CS), pin2 (DO), pin5 (DI) of below waveform.
2) If pin1, 2, 5, 6 doesn’t come out, check registers (R563, R564, R534, R535, R536, R5E4) of IC503.
 If registers of IC503 is OK, then replace IC503. (it need to download program.)
3) After change IC503, if It is still not below waveform, check IC501 (DSP IC).
4-3-3. Service hint (Any picture/ Remark)
VCC
CLK
DO
CS#
< Signal waveform >
< MAIN board bottom view >
IC503
IC503
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3-9
ONE POINT REPAIR GUIDE
5. 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.
5-1. SPINDLE MOTOR
5-1-1. Solution
Replace IC400 on MAIN board.
5-1-2. How to troubleshoot (Countermeasure)
1) Check the SPDO signal from pin16 of IC401.
 If no signal, check DVCC_3.3V and DV 3.3V (RF) and X400.
2) Check the SPIN+ & SPIN- from IC400 to CN401 for driving SPINDLE motor. It is about 3.6 Vp-p.
 If no signal, check M_5 V for IC400.
3) Check if the FFC cable is solidly connected between CN401 and MD.
4) Check the MD.
 If the spindle motor is sort-circuit or has any trouble, it can not rotate CD discs.
Please check the function after changing another MD.
5-1-3. Service hint (Any picture/ Remark)
< Waveform of SP- & SP+
for driving SPINDLE motor >
< MAIN board top view >
SP+: pin18
SP+: pin18
SP-: pin19
SP-: pin19
IC400
IC400
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3-10
ONE POINT REPAIR GUIDE
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.
5-2. SLED MOTOR
5-2-1. Solution
Replace IC400 on MAIN board.
5-2-2. How to troubleshoot (Countermeasure)
1) Check the SLDO signal from pin15 of IC401.
 If no signal, check DVCC_3.3V and DV 3.3V(RF) and X400.
2) Check the SPED+ & SLED- from IC400 to CN401 for driving SPINDLE motor. It is about 2.9 Vp-p.
 If no signal, check M_5 V for IC400.
3) Check if the FFC cable is solidly connected between CN401 and MD.
4) Check the MD.
 If the spindle motor is sort-circuit or has any trouble, it can not rotate CD discs.
Please check the function after changing another MD.
5-2-3. Service hint (Any picture/ Remark)
< Waveform of SLED- & SLED+
for driving SLED motor >
SP-
SP+
< MAIN board top view >
SLED+: pin11
SLED+: pin11
SLED-: pin12
SLED-: pin12
IC400
IC400
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3-11
< Waveform
for driving tray open/ close motor >
MOT_ CL OS E
MOT_ OP EN
LO+(RED)
LO-
ONE POINT REPAIR GUIDE
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.
5-3. TRAY OPEN/ CLOSE MOTOR
5-3-1. Solution
Replace IC400 on MAIN board.
5-3-2. How to troubleshoot (Countermeasure)
1) Check MOT_OPEN & MOT_CLOSE signals from pin P5, L4 of IC501 to IC400.
 If no signal, check M_5V to IC400.
2) Check LOAD± from IC400 to CN401 for driving the tray open / close motor. It is about 3.85 Vp-p.
 If no signal, check M_5V to IC400. If it has any trouble, replace it with a new one.
3) Check if the FFC cable is solidly connected between CN401 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.
Please check the function after changing another MD.
5-3-3. Service hint (Any picture/ Remark)
< MAIN board top view >
MOT_CLOSE: pin6
MOT_CLOSE: pin6
MOT_OPEN: pin7
MOT_OPEN: pin7
LOAD+: pin9
LOAD+: pin9
LOAD-: pin10
LOAD-: pin10
IC400
IC400
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3-12
ONE POINT REPAIR GUIDE
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.
5-4. LASER TRACKING ACTUATOR
5-4-1. Solution
Replace IC400 on MAIN board.
5-4-2. 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 pin14 of IC401.
 If no signal, check DVCC_3.3V & DV_3.3V (RF) and X400.
2) Check TR- & TR+ from IC400 to CN400 for driving the tracking actuator.
 If no signal, check M_5V for IC400.
3) Check if the FFC cable is solidly connected between CN400 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.
Please check the function after changing another MD.
5-4-3. Service hint (Any picture/ Remark)
< Waveform of TR±
for driving tracking actuator >
< MAIN board top view >
TR+: pin16
TR+: pin16
TR-: pin15
TR-: pin15
IC400
IC400
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3-13
ONE POINT REPAIR GUIDE
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.
5-5. LASER FOCUSING ACTUATOR
5-5-1. Solution
Replace IC400 on MAIN board.
5-5-2. 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 FDO signal from pin13 of IC401.
 If no signal, check DVCC_3.3 & DV_3.3V(RF) and X400.
2) Check F- & F+ from IC400 to CN400 for driving the focusing actuator.
 If no signal, check M_5V for IC400.
3) Check if the FFC cable is solidly connected between CN400 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.
Please check the function after changing another MD.
5-5-3. Service hint (Any picture/ Remark)
< Waveform of F±
for driving focusing actuator >
< MAIN board top view >
F+: pin14
F+: pin14
F-: pin13
F-: pin13
IC400
IC400
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3-14
ONE POINT REPAIR GUIDE
6. NO SOUND
There is no sound output by DIGITAL AUDIO AMP DAMAGE, repair the set according to the
following guide.
6-1. DIGITAL AUDIO AMP DAMAGE
6-1-1. Solution
Replace IC701, IC702 on MAIN board.
6-1-2. 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.
2) Check PVDD.
 If PVDD is abnormal, check the SMPS.
3) Check AMP_12V for driving the gate of AMP IC.
a. All the powers are normal, but if AMP_12V 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 AMP_12V 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.
6-1-3. Service hint (Any picture/ Remark)
< MAIN board top view >
IC701
IC701
L703
L703
L702
L702
L701
L701
L704
L704
IC702
IC702
IC601
IC601
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3-15
ONE POINT REPAIR GUIDE
NO SOUND
There is no sound output in the CD FUNCTION, repair the set according to the following guide.
6-2. CD FUNCTION
6-2-1. Solution
Replace IC501 on MAIN board.
6-2-2. How to troubleshoot (Countermeasure)
1) Check CD_BCK, CD_LRCK, & CD_DATA signals from IC501 to IC401.
 If no signal, check if the RF & servo signals from MD is entered to IC401.
Refer to the “No operation of MD” guide on Item 5.
2) Check the following I2S signal flow. < I2S audio signal Interface >
- MCS_BCK : IC501_pin E1 --> IC601_pin23
- MCS_LRCK : IC501_pin D1 --> IC601_pin22 (44.1 kHz)
- MIX_DATA0_OUT : IC501_pin E2 --> IC601_pin24
- MCS_MCLK : IC501_pin D2 --> IC201_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.
6-2-3. Service hint (Any picture/ Remark)
< Waveform of I2S audio interface signals >
< MAIN - CD DSP circuit >
< MAIN board top view >
IC501
IC501
R503
R503
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3-16
ONE POINT REPAIR GUIDE
NO SOUND
There is no sound output in the USB Function, repair the set according to the following guide.
6-3. USB FUNCTION
6-3-1. Solution
Replace IC204 on MAIN board.
6-3-2. 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 USB_5V to pin5, 6 of CN803.
2) Check USB D1± or USB D2± from MAIN board to TOP 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 CN502(pin1, 2, 8, 9).
 If there is any trouble, check the power for IC204.
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 6-1 is normal.
6-3-3. Service hint (Any picture/ Remark)
USB D-/D+ (CN502 pin1, 2 & pin8, 9)
< Waveform of USB D± signal >
D
D+
D-
< MAIN board top view >
CN502
CN502
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3-17
ONE POINT REPAIR GUIDE
NO SOUND
There is no sound output in the AUX Function, repair the set according to the following guide.
6-4. AUX FUNCTION
6-4-1. Solution
Replace IC201 on MAIN board.
6-4-2. 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 DVCC_5V & DVCC_3.3V (ADC) for IC201. If is NG, replace it a new one.
4) Check the following I2S signal flow from IC501 to IC601. (Refer to Item 6-2.)
 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. Refer to “Digital Audio AMP” guide on Item 6-1.
 If AMP is damaged, replace it with a new one.
6-4-3. Service hint (Any picture/ Remark)
< AUX function signal flow > < MAIN board bottom view >
MCS_BCK: pin42
MCS_BCK: pin42
MCS_LRCK: pin43
MCS_LRCK: pin43
MCS_MLCK: pin44
MCS_MLCK: pin44
IC201
IC201
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3-18
ONE POINT REPAIR GUIDE
NO SOUND
There is no sound output in the TUNER function, repair the set according to the following guide.
6-5. TUNER FUNCTION
6-5-1. Solution
Replace IC201 on MAIN board.
6-5-2. How to troubleshoot (Countermeasure)
1) Check if TUNER_LR is entered from pin1, 3 of TU500 to IC201 (pin26, 27).
 If no signals, check DVCC_3.3V 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 DVCC_5V & DVCC_3.3V (ADC) for IC201. If is NG, replace it with a new one.
4) Check the following I2S audio signal flow from IC501 to IC601. (Refer to Item 6-2.)
 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. Refer to “Digital Audio AMP” guide on Item 6-1.
 If AMP is damaged, replace it with a new one.
6-5-3. Service hint (Any picture/ Remark)
< TUNER function signal flow > < MAIN board bottom view >
TUNER_L: pin26
TUNER_L: pin26
TUNER_R: pin27
TUNER_R: pin27
IC201
IC201
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3-19
NO SOUND
There is no sound output in the PORTABLE Function, repair the set according to the following guide.
6-6. PORTABLE FUNCTION,
6-6-1. Solution
Replace IC201 on MAIN board.
6-6-2. How to troubleshoot (Countermeasure)
1) Check if PT_LR 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 DVCC_5V & DVCC_3.3V (ADC) for IC201. If is NG, replace it with a new one.
4) Check the following I2S audio signal flow from IC501 to IC601. (Refer to Item 6-2.)
 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. Refer to “Digital Audio AMP” guide on Item 6-1.
 If AMP is damaged, replace it with a new one.
6-6-3. Service hint (Any picture/ Remark)
< PORT. IN function signal flow >
ONE POINT REPAIR GUIDE
< MAIN board bottom view >
PT_L: pin9
PT_L: pin9
PT_R: pin10
PT_R: pin10
IC201
IC201
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3-20
ONE POINT REPAIR GUIDE
NO SOUND
There is no sound output in the MIC IN function, repair the set according to the following guide.
6-7. MIC IN function
6-7-1. Solution
Replace IC206 on MAIN board, ICA301 on TOP FRONT board.
6-7-2. How to troubleshoot (Countermeasure)
1) Check MIC_SI & MIC_S2 signal to pin5 & 6 of CN201.
 If no signal, Check the signals to pin6 & 8 of CNA301 on the FRONT board.
Check if the signal is entered from pin 6 & 8 of CNA301 to pin 5 & 6 of CN201.
2) Check if MIC_SIG is entered from pin 6 of JK302 & JKA303 to pin2, 13 to ICA301 (PRE AMP).
3) Check if the amplified signal comes out from pin3 &12 of ICA301.
 If no signal output, check DVCC_3.3V for ICA301, replace ICA301 with a new one if it has a problem.
4) Check if MCS_BCK, MCS_MLCK & MCS_LRCK is entered from IC501 to IC206.
Check if MIC_DATA_IN is entered from pin9 of IC206 to pin T1of IC501.
 If no signal, check DVCC_5V & DVCC_3.3V for IC206.
If it is abnormal, change replace it a new one.
5) Check the following I2S signal flow from IC206 to IC501.
 If there is any trouble, check the power for each IC.
If the signals are abnormal, replace it a new one.
6) Check if the digital audio AMP block is okay. Refer to “Digital Audio AMP” guide on item 6-1.
 If AMP is damaged, replace it with a new one.
6-7-3. Service hint (Any picture/ Remark)
IC206
IC206
ADC/ MIC_DATA: pin9
ADC/ MIC_DATA: pin9
MCS_BCK: pin8
MCS_BCK: pin8
MCS_LRCK: pin7
MCS_LRCK: pin7
MCS_MCLK: pin6
MCS_MCLK: pin6
< MAIN board bottom view >
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3-21
ONE POINT REPAIR GUIDE
NO SOUND
There is no sound output in the Bluetooth function, repair the set according to the following guide.
6-8. BLUETOOTH FUNCTION
6-8-1. Solution
Replace IC501 on the MAIN board or bluetooth module on the FRONT Panel.
6-8-2. How to troubleshoot (Countermeasure)
1) Check BT_RX, BT_TX signal to pin6, 4 of CN504.
 If no signal, check the signal to pin4, 6 and pin10 (BT_3.3V) of on the Bluetooth module
and cable connection state.
 If there are no signal out from module, replace new module.
2) Check if BT_RX/TX is entered from pin6, 4 of CN504 to pin L1,K1 to IC501 (DSP).
3) Check if MCS_BCK, MCS_LRCK & MIX_DATA IN is entered from IC501 to IC601.
 If no signal, check +3.3 VA & +1.2 VA for IC501.
If it is abnormal, change 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.
If the signals are abnormal, replace it a new one.
5) Check if the digital audio AMP block is okay. Refer to “Digital Audio AMP” guide on item 6-1.
 If AMP is damaged, replace it with a new one.
6-8-3. Service hint (Any picture/ Remark)
IC501
MLC3730 IC601
TPS5548DGG
PWM
MCS_BCK
MCS_LRCK
MIX_DATA0_OUT
TPS5631B
AMP
B/T Module
BT_RX,
BT_TX
< Bluetooth function signal flow > < MAIN board bottom view >
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