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EN 28
5.
Q522.3E LA
5.8
Fault Finding and Repair Tips
Read also paragraph "Error Codes" -> "Error Buffer" -> "Extra
Info".
5.8.1
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...)
5.8.2
DC/DC Converter
Introduction
•
The best way to find a failure in the DC-DC converters is to
check their starting-up sequence at "power-on via the
mains cord", presuming that the stand-by microprocessor
is operational.
•
If the input voltage of DC-DC converters is around 12.7 V
(measured on decoupling capacitors 2U0W and 2U0Y) and
the enable signals are "low" (active), then the output
voltages should have their normal values. The +1.2 V
supply starts-up when +12 V appears, then at least 100 ms
later, the +3.3 V will be activated via the ENABLE-3V3
signal from the stand-by microprocessor. If +12 V value is
less than 10 V then the last enumerated voltages will not
show-up due to the under-voltage detection circuit 7U01-1
+ 6U04 and surrounding components. Furthermore, if
+12 V is less than 8 V then also +1.2 V will not be available.
•
The consumption of controller IC 7U0A is around 19 mA
(that means almost 200 mV drop voltage across resistor
3U70).
•
The current capability of DC-DC converters is quite high
(short-circuit current is 7 to 10 A), therefore if there is a
linear integrated stabiliser that, for example, delivers 1.8 V
from +3.3 V with its output overloaded, the +3.3 V stays
usually at its normal value even though the consumption
from +3.3 V increases significantly.
•
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: +1.2 V not present (only for a short while
~10 ms)
1. Check 12 V availability (resistor 3U70, MOS-FETs
7U05 and 7U06), value of +12 V, and surrounding
components).
2. Check the voltage on pin 9 (1.5 V).
3. Check for +1.2 V output voltage short-circuit to GND
that can generate pulsed over-currents 7 to 10 A
through coil 5U00.
4. Check the over-current detection circuit (2U00 or 3U17
interrupted).
•
Symptom: +1.2 V present for about 100 ms, +3.3 V not
rising.
1. Check the ENABLE-3V3 signal (active "low").
2. Check the voltage on pin 8 (1.5 V).
3. Check the under-voltage detection circuit (the voltage
on collector of transistor 7U01-1 should be less than
0.8 V).
4. Check for output voltages short-circuits to GND
(+3.3 V) that can generate pulsed overcurrents
7 to 10 A through coil 5U01.
5. Check the over-current detection circuit (2U04 or 3U14
interrupted).
•
Symptom: +1.2 V OK, +2.5 V and +3.3 V present for
about 100 ms. Possible cause: SUPPLY-FAULT line
stays "low" even though the +3.3 V and +1.2 V is available
Service Modes, Error Codes, and Fault Finding
5.8.3
- the stand-by microprocessor is detecting that and
switching "off" all supply voltages.
1. Check the drop voltage across resistor 3U70 or 3U3T
(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
7U0A is less than 14 V (should be 19 V).
3. Check if +1.2 V or +3.3 V are higher than their normal
values. That can be due to defective DC feedback of
the respective DC-DC convertor (ex. 3U1J, 3U75)
•
Symptom: +1.2 V or +3.3 V show a high level of ripple
voltage (audible noise can come from the filtering coils
5U00 or 5U01). Possible cause: instability of the
frequency and/or duty cycle of a DC-DC converter or
stabiliser.
1. Check the resistor 3U0H and 3U2E, capacitors 2U0C
and 2U0A, input and output decoupling capacitors.
2. Check a.c. feedback circuits
(2U08+2U09+3U07+3U08 for +1.2 V and
2U03+2U05+3U04 for +3.3 V)
Note: when a pair of power MOSFETs (7U08-1/2 or 7U05-1/
22) becomes defective, the controller IC 7U0A must be
replaced as well.
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.
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