PHILIPS VARADAAN [ZAPPA]_ SMD UOC 14 / 20 & 21PT2216_Troubleshooting
Troubleshooting
SMPS Philips Varadaan (Zappa)
SMPS
control IC used: TEA1507p: 8pin DIL [Dual In Line]
IC
pin function & voltages.
1. Vcc
> 13.8V
2. Ground
3. Control
Input > 1.3V
4. Start-up
current source > 0V
5. Current
Sense > 0V
6. Output
to FET Gate > 2V
7. Not conntected
8. Input voltage from mains for start0up > 15VDC to 18VDC.
The
most common fault that I’ve came across to this circuit was the failure of the
SMPS switching control IC [TEA1507P].
To
detect whether this IC is faulty is so easy.
Check
the voltage at pin-8. If the IC is
working; about 15.3VDC will be present at this pin. If not; this voltage will go up tp 200VDC.
If
you found this voltage to be abnormal (much higher than 16VDC or so); the IC
should be suspected.
Before
confirm it, check all the other pin voltages as stated above.
If
there is 15V at pin 8, and still the IC does not oscillates; check the voltage
at pin 1. Should measure about
13VDC. If it is absent, the IC is
faulty; even though the voltage at pin 8 is OK.
These
two voltage checks are more than enough to confirm the working condition of
this IC.
Another
fault that can occur is the absence of voltage at pin-8. If so, check R3527 (2.2Kohms) resistor for
open or loose soldering. The main
working voltage comes to IC from main rectified voltage is through this
resistor. But this fault is very rare.
If
you measure the voltage at pin8-8 of the IC is OK, but there is no voltage at
pin-1; check the zener diode connected to ground from this pin for short.
Failure
to the FET [STP5NC50FP] is rare, but can happen due to lightning or other high
voltage spikes. To make sure about it,
check the resistor connected to ground [R3526 – 0.15Ohms]; from the ‘source’
terminal of this FET. If it is found
opened, be sure that the Source to Drain junction inside the FET is shorted..in
this case, it must be replaced before switch ON the set. Otherwise the TEA1507P will get damaged.
Just
see the track of FET. If R3526 is
opened; and the Source to Drain junction is shorted, the voltage at the Drain
terminal will pass in to the IC through R3524 & R3525. This voltage will be high, approximately
equal to the rectified main DC voltage and will damage the IC.
When
you check this circuit, do all the checks as stated above, before switch ON the
set.
If
lightning stroke is suspected, check all the rectifier diodes D6500, D6501,
D6502 & D6503. Even though they
measure good, will be best to replace all of these diodes, as they might poise
problem with time. If any one of these
diodes get shorted, the AC protection fuse will blow up. So, if you see a blown up fuse with this set,
of any other model SMPS circuit; check
all these four diodes and 2 ceramic capacitors (connected in parallel to two of
these diodes); C2501 & C2502, for leak.
Failure
to SMPS transformer is very rare case. I
haven’t seen it so far with these model sets.
Another
component to check is the opto-coupler TCET1103(G). I’ll replace this component for each service
to SMPS; whatever its condition may be; either measure good or not.
If
FET is found shorted, check and replace C2523 (1.5Kpf). if this capacitor is open or has loose solder
terminals the FET will get shorted at the moment you switch ON the set. You’ll get no time for any check. So, take a special care to this capacitor.
If
set show any start-up problem; check and replace the transistor 7522
(BC847B). check all the associated
component to this transistor for any damage.
Most
of the components with this set are SMDs [Surface Mount Devices]. This will make service rather difficult; but
can do it ease, if you’ve proper tools to work with SMDs.
Before
switch ON the set, desolder out L5561, connected to main SMPS power voltage
output to LOT and related components. To
this set, short circuit protection is very sensitive, and so if there is any
short circuit at the main board; the set won’t witch ON, even though the SMPS
voltages are OK. After unsolder the
above coil from circuit; connect a filament type bulb [Do Not use CFL or any
other types]; across the tow terminals of C2561 (47MFD); and switch the set
ON. Measure the voltage across the two
terminals of C2561. It should be around
95VDC. A slight variation is tolerated. The bulb will glow dim. Keep this load for at least 15 minutes and
check the voltage. This voltage should
be steady. This is the SMPS voltage
check. Mke sure that there is no
variation to this voltage with time.
If
all are found OK, disconnect the set from AC mains; re-connect the coil 5561;
disconnect the bulb; and switch ON the set.
If
there is no more problems to main board components, the set should switch on,
and the raster should appear.
If
standby LED blinks and the set do not start up, check and replace damaged
component/s at its horizontal output stage.
Check Horizontal Output Transistor, LOT, deflection yoke and so.
The
blinks are fault codes as you know. From
the number of blinks, you can get an idea about the faulty stage. For more details about the blinking codes to
Philips TVs, refer by this site.
Blinking codes to Philips TVs are given.
Counting the number of blinks to Philips TVs is entirely different to that of other TVs. It is not a direct count procedure. This site itself has details about how to count the number of LED blinks [Fault Codes] to Philips brand TVs. Surf this site with patience. Pull up older posts here.
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