Sony Wega

SONY WEGA SERIES TVs – KV-HA21M50_KV-HA21M80_KV-HA21M80/H_KV-HA21M81_KV-HA21P52_KV-HA14M80 & KV-HW21M83 : POWER SUPPLY FAULTS

The set will be dead, no standby light, no response to power.

Section - 1

The power supply section of the set is dead.

      We
have to begin with its ON/OFF switch first. Check the ON/OFF switch for
its pole continuity. On rare cases, any one pole of the power switch
will be defective.  The switch is a DPST [Double Pole Single Throw] type.  If
any one among these poles has an internal contact defect, no power will
get into the power regulator of the set and thus dead condition.

     If switch is found OK, come towards fuse [F600 – 3.15 Amps].  All
component numbers here se refer can be seen on its printed circuit
board, printed on both component and foil side. If fuse is found blown
up, take a pause.  Never put any more fuse, as there will be specific reason for this fuse to blow up.  We must find it out first.  If
we insert a fuse without rectifying the problem to which the present
fuse has been blown up, it may make more damage to components. Fuse is
used here as a protection device to any short-circuit that may occur to
internal circuits.  Just find the reason for its failure, is the first thing to do. Just follow the circuit.

     A special care should take before power up this chassis.  We must have to detach the degauss coil connection plug out to place the main board in service position.  Here the set uses one posistor [THP 600] with three terminals.  A resistor [470Ohms/3W] is connected with its terminal [1] to AC supply line.  Desolder this resistor out, or just lift up a little to get it disconnected from the circuit.  Otherwise,
a tremendous current will follow through this resistor without degauss
coil connected, when we switch ON the TV after fuse replacement. It is
best to desolder out the degaussing posistor out from it, till all the
other work has been done and resolder it after. Moreover, if this posistor has shorted internally, the fuse will blow out as soon as we switch ON the TV.  If
fuse does not blow out when this posistor has been removed from the
printed circuit board, we can make sure that the short inside this
posistor caused the fuse to blow out.  If this is the case, without this posistor, the set should work well.  Then we have to replace this posistor only. The work is over.

     The next
step is to check the mains bridge rectifier [D601] and mains filter
capacitor [C603]. But before checking these come towards the ‘switching
regulator’ IC [D600 – STR F6707A], a most susceptible component in power
supply section.  Locate its pins (1&2).  Check the resistance between these two terminals.  It should never show a short (less than 1k).  If
found very low resistance, desolder out this component from the circuit
board. No check the resistance across +ve and –ve terminals of the
mains filter capacitor.  It
should be high. Before touching these terminals with probes of
millimeter, properly discharge the capacitor; otherwise, multimeter will
get damaged. 

Continued on section-2