SONY WEGA SERIES TVs – KV-HA21M50 - KV-HA21M80 - KV-HA21M80/H - KV-HA21M81 - KV-HA21P52 - KV-HA14M80 & KV-HW21M83 : POWER SUPPLY FAULTS

 

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

SONY WEGA SERIES TVs – POWER SUPPLY FAULTS

KV-HA21M50_KV-HA21M80_KV-HA21M80/H_KV-HA21M81_KV-HA21P52_KV-HA14M80 & KV-HW21M83 : POWER SUPPLY FAULTS

       We have already reached half the way by troubleshooting power supply section.  We have found that here is no fault with mains ON/OFF switch, Rectifier Bridge, switching regulator IC, posistor.  The main component to check further is (R610 – 33Kohms 3W) resistor, which supplies voltage to the internal circuits of the switching IC.  This is one among the important test point.  Check the voltage at (Pin-4) of regulator IC.  If there is no voltage, check this resistor for open.  If it is found OK, check the zener diode (D603) for short.  Replace it, it is best.  If switching regulator IC found shorted, you have to check all the components on the primary side of the SMPS power supply.  Even a small ceramic capacitor can cause severe trouble to switching power section.

      It is recommended to use a 100W filament type bulb at the secondary [135] VDC line, after disconnecting (R502), the serial resistor connected to LOT power supply.  You can reconnect this after finishing the power supply work. When a set comes to you for repair, with dead power regulator section, with shorted switching IC [STR F6707A], be very careful, and check all other components, for any short, open or any other trouble.  Replace these components, even if they are found good. [C610, D605, R608, R605, D603&C606]. If power regulation is found poor, check and replace (IC602 – SE135N) and optocoupler (PH600).  If STR are is found shorted, you have to replace all the above mentioned components, otherwise the newly replaced STR may get fail, as soon as you switch ON the set. 

Check all the solder terminals of SMPS transformer, and other components for loose soldering.  This is the main fault for most of the Sony set.  Resolder all the suspected solder points by applying a little more solder, without making any solder bridge short in between adjacent solder points.

 

C 623 & C 602 are very important capacitors, even though they are very small.  Replace both of them with same value.