SONY KV EF29M - CRT TV TROUBLESHOOTING

Fault:  Dead set.

     Check ON/OFF switch, for contact break if any.  If it is OK, check fuse (F1690).  The fuse can be located at [H7] board, just near to the ON/OFF switch.  If found open, never put an other fuse in place, till the reason for the blowing of fuse is detected.

 

     Desolder out the degaussing thermistor (THP 2600).  If this posistor has short inside, fuse will blow up. Check the bridge rectifier and associated components, disc ceramic capacitors [D2600, C2607, C2606] for any short.  Check them with an analogue multimeter set to Kohms range.  If any  reverse leak found, replace that component.  If bridge rectifiers have shorted diodes inside, may cause fuse to blow. Even a single diode inside it has the short, it will cause a blown up fuse, as soon as you switch ON the set.

     If bridge rectifier, and all other related components are found OK, measure the resistance across (C2617 – 560MFD__450VDC).  Set an analogue multimeter to Ohms range and check.  Under no conditions, the meter should read below 500Oms.  If it reads below this range, make sure that the power regulator control IC (IC601_STR S6709N) is faulty.  Resolder this IC out from circuit.  Now check the resistance across C2617.  If found high, STR_S6709 is defective.

 

Before replacing this regulator IC, the other components connected with this IC should be checked. Check these components one by one.  [ R618_0.1Ohms, D603, C603, R604, D601_8.2V ZENER DIODE, and Q600 [2SD1640Q].  It is advised to replace these components, before replacing a shorted STR. Replace the capacitor [C605_100Pf-3KV].  Replace the optocoupler, [IC603_ON3171R] as a precautionary measure.

 

After replacing all these components, disconnect [R886_1.2Ohms 2W], current limiting resistor to LOT, connect a 100W filament bulb in series with the V+ve supply line, and switch ON the set, keep it at this condition for about 10 minutes or so, make sure that the B+ve voltage is steady all the time.

Connect reconnect R886 back, and check the set.

If STR regulator has found defective, never replace it without checking other connected components to it.  Especially, the Zener Diode [D601].  It will get damaged along with the STR, when it gets shorted.  Even though, it may measure good, it is best to replace it along with STR. Any fault to this diode will cause an other STR failure.
All component numbers showed here can be seen printed on either side of the printed circuit board.