TDA8873 SYSCON-CHROMA IC – CIRCUIT TROUBLESHOOTING
Some
Faults that can occur due to defects to this IC are:
Power
does not switch ON.
TV/AV
selection is not possible.
Picture
lacks black level.
Tuner
does not work.
No
EHT.
Horizontal
Output Transistor fails frequently.
Audio
problems.
Out
of synchronized picture.
Displaced
picture [horizontally]
Before
proceed to troubleshoot, make sure that the SMPS section circuit is woking
properly and all the secondary voltages generated are present. Check the +5VDC & +8VDC. These two voltages are the supply voltages to
TDA8873. If all these voltages are
present, and still the IC do not work, we can assume that the IC is defective. Check the main supply voltage; 8VDC at
pin-17. The 8VDC is supplied to this pin
only. No other pins receives this
voltage. Check this voltage first.
If
it is OK, proceed.
If
not, check V507-2SC8080 transistor and associated components at the SMPS
section circuit.
Assuming
that this voltage is OK;
Check
the voltages at these pins; 3,9,36 & 55.
At all these pins, the voltage should be 5VDC. If absent, check the 5V voltage regulator IC
used at SMPS section, IC607-78L05 & transistor V505-C8050 and related
components.
Here
one point to note is, with the SMPS circuit used here with this circuit; if
there is no 8VDC; the 5VDC too will be absent.
Assuming
that all the voltages stated above are Ok; but the IC do not function:
If
so; the first check should be concentrated toward the soldering terminals of
the IC. There are 64 pins. If any of these pins have loose solder,
erratic symptoms will be the result. So;
first make sure that these solder terminals are OK; and have no dry solder
points. Normally it will be too
difficult to detect a dry solder terminal, as it will be too microscopic for
normal vision. So it will be the best
practice to re-solder all these 64 pins; by applying a little more fresh solder
to each terminals, without making any solder-bridge short in between adjacent
terminals. Be sure not to apply too much
heat for long time, at these termilas, as it might damage the IC. The soldering should be done as fast as
possible; and should be clean.
Now
check all the other pin voltages.
Measure
the voltages at SCL & SDA [Serial Clock & Serial Data] pins; 58 &
57 respectively. Both of this should be
around 2.8VDC. if any of these voltages
are either too low or high; the IC is defective.
No
repair. Replacement is the only remedy.
Next
check the Power-ON signal voltage present at pin 64. When you press the Power On button on the
remote control, this voltage should be vary to High/Low [4.8VDC.0.5VDc.]
If
not; the IC is defective. The system control section inside it does not work
properly.
Check
the voltage at pin-5. This is the Reset
voltage to IC and should come around 3.2VDC.
if absent; check Q203-A1015 and Zener diode VD201, connected to its base
terminal.
Assuming
that all the above voltages are normal:
Measure
the voltage at pin-13 [horizontal out signal].
It should be about 0.4 to 0.7VDC.
will have an oscillating frequency of ~ 15.625KHz. if your meter is capable of measuring
frequency; you can measure this frequency directly from this point. If this
frequency and the voltage at these terminals is abnormal, the IC is defective.
In
most cases; measuring the voltages said above will reveal the condition of this
IC; whether defective or good.
Click on the schematic to zoom in
