LCD TV FAULT FINDING TIPS
|
Fault Finding and Repair Tips
|
Ambilight
Due to the degeneration process off the ambilights, it is recommended to change both ambilight units in case one unit needs to be repaired.
Audio Amplifier
It is recommended to replace all components at once 7D06, 7D09, 3D01, 3D25 when a defect FET 7D10 need to be fixed. For the left channel (defect FET 7D35) of the audio amplifier replace all components like 7D31, 7D34, 3D11, 3D28.
CSM
When you activate CSM and there is a USB stick connected to the TV, the software will dump the complete CSM content to the USB stick. The file (Csm.txt) will be saved in the root of your USB stick. If this mechanism works you can conclude that a large part of the operating system is already working (Mips, USB...) |
Introduction
|
# The best way to find a failure
in the DC-DC converters is to check their starting-up sequenceat power-on via
the mains cord, presuming that the stand-byμP is operational.
# If the input voltage of DC-DC converters is around 12.7V (measured on decoupling
capacitors 2U03/2U93/2U6S and 2U6R) and the enable signals are low (active)
then the output voltages should have their normal values.+12V and +5V-POD
supplies start-up first (enabled by POD-MODE signal from the stand-by
microprocessor). There is a supplementary condition for +12V to start-up: if
+5V-POD doesn’t start up due to a local defect then +12V will not be available,
as well.+5V-ONsupply is enabled by the ONMODE signal (coming also from the
stand-by microprocessor) and is coming up a little bit later (20ms) due to
the slower rise time needed to charge the USB decoupling capacitor 2N31. +1V2
supply starts-up when +12V appears, then at least 100ms later, +1V8, +2V5 and +3V3 will be
activated viaENABLE-3V3 signal from the stand-by microprocessor.If +12V value
is less than 10V then the last enumerated voltages will not show-up due to the
under-voltage detection circuit 6U10 + 7U10 and surrounding components. Furthermore,
if +12V is less than 8V then also +1V2 will notbe available. The third dc-dc convertor
that delivers +1V4out of +12V is started up when the ENABLE-1V2 becomes active
(low) and +12V is present. The +Vtun generator (present only for the analog version
of China platforms) will generate +33V for the analog tuner as soon as
the12V/3.3V DC-DC converter will start to operate.
# The consumption of controller IC 7U00 is around 19mA (that means almost 200mV drop voltage across resistor 3U01) and the consumption ofcontroller IC 7U64 is around 12mA. # The current capability of DC-DC converters is quite high (short-circuit current is 7 to10A), therefore if there is a linear integrated stabilizer that, for example delivers 1.8V from +3V3 with its output overloaded, the +3V3 stays usually at its normal value even though the consumption from +3V3 increases significantly. # The +1V8 and +2V5 supply voltages are obtained via linear stabilizer made with discrete components that can deliver a lot of current, therefore in case +1V8 or +2V5 are short circuited to GND then +3V3 will not have the normal value but much less. # The SUPPLY-FAULT signal (active low) is an internal protection (error 9) of the DC-DC convertor and will occur if the output voltage of any DC-DC convertor is out of limits (10% of the normal value). |
Fault
Finding
|
# Symptom: +1V2 not present
(even for a short while ~10ms)
1. Check 12V availability(resistor 3U01, MOS-FETs 7U03 and 7U08), value of +12 V, +12 V switch (7U14 + 7U16 and surrounding components) and +5V-POD. 2. Check the voltage on pin 9 (1.5V), 3. Check for +1V2 output voltage short-circuit to GND that can generate pulsed over-currents 7...10 A through coil 5U02. 4. Check the over-current detection circuit (2U20 or 3U40 interrupted). # Symptom: +1V4 not present (even for a short while ~10ms) while +12V is ok (also across input capacitors 2U6S and 2U6R). 1. Check resistor 3U7B and power MOS-FETs 7U61-1/2 2. Check the voltage on pin 4(4V) 3. Check enable signal ENABLE-1V2 (active low) 4. Check for +1V4 output voltage short-circuit to GND that can generate pulsed over-currents 7...10A through coil 5U65. Check the over-current detection reference (2U65 + 3U7C) and the boot components (2U66 + 6U60). # Symptom: +1V2 present for about 100ms, +1V8, +2V5 and +3V3 not rising 1. Check the ENABLE-3V3 signal (active LOW), 2. Check the voltage on pin 8 (1.5V), 3. Check the under-voltage detection circuit (the voltage on collector of transistor 7U10-1 should be less than 0.8V), 4. Check for output voltages short-circuits to GND (+3V3, +2V5 and +1V8) that can generate pulsed over currents 7...10A through coil 5U01, 5. Check the over-current detection circuit (2U18 or 3U31 interrupted). # Symptom: +1V2 OK, +2V5 and +3V3 present for about 100ms.
Possible cause: SUPPLY-FAULT line stays low even though the +3V3 and
+1V2 is available - the stand-by μP is detecting that and switching off all
supply voltages.
1. Check the drop voltage across resistor 3U01 or 3U7B (they could be too high, meaning a defective controller IC or MOS-FETs), 2. Check if the boost voltage on pin 4 of controller IC 7U00 is less than 14V (should be 19V), 3. Check if +1V2 or +3V3 are higher than their normal values - that can be due to defective DC feedback of the respective dc-dc convertor (ex.3U47, 3U77, 3U7L, 3U7J or 3U70). # Symptom: +1V2, +1V4, +1V8, +2V5 or +3V3 shows a high level of ripple voltage (audible noise can come from the filtering coils 5U01, 5U02 or 5U60).
Possible cause: instability of the
frequency and/or duty cycle of a dc-dc converter or stabilizer.
1. Check the resistor 3U32 and 3U7D, capacitors 2U17 and 2U19, input and output decoupling capacitors. 2. Check a.c. feedback circuits (2U23+2U24+3U55+3U63 for +1V2, 2U6D+2U6E+2U6G+3U6A+3U7E for +1V4 and 2U07+2U08+3U17+3U24 for +3V3), compensation capacitors 2U25, 2U34, 2U36, 2U37, 2U40, 2U43, 2U68 and 2U6B. # Symptom: +1V2, +1V4, +2V5 and +3V3 ok, no +Vtun (analog sets only).
Possible cause: the “+VTUN GENERATOR”
circuit (7U24+7U26+surroundings components) is defective: check transistor
7U24 (it has to have gate voltage pulses of about 10V amplitude and drain voltage
pulses of about 35V amplitude) and surroundings components. A high
consumption (more than 6mA) from
+Vtun voltage can cause also +Vtun voltage to be too low or zero. Note: when a pair of power MOSFETs(7U01+7U06, 7U03+7U08 or 7U61-1/2) becomes defective the controller IC 7U00 or 7U64 should be replaced as well. |
Display Option code
|
Attention: In case you have
replaced the SSB, always check the display option code in SAM, even if you
have picture. With a wrong display option code it is possible that you will
have picture, but in certain conditions you can have unwanted side effects.
|
Exit “Factory Mode”
|
When an “F” is displayed in the
screen's right corner, this means that the set is in “Factory” mode, and it
normally happens after a new SSB has been mounted. To exit this mode, push the
“VOLUME minus” button on the TV’s keyboard control for 5 seconds and restart
the set.
|
