Sony KDL-50W7 C Series Service Manual Download

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3) Measuring the voltage drop across a resistor by means of a VOM or battery
operated AC voltmeter. The 'limit' indication is 0.75V so analog meters must
have an accurate low voltage scale. The SIMPSON'S 250 and SANWA SH-
63TRD are examples of passive VOMs that are suitable. Nearly all  battery
operated digital multimeter that have a 2 VAC range are suitable.
(see Figure 2.)

1-4. Safety Check-Out

After correcting the original service problem, perform the following

safety checks before releasing the set to the customer:-

1) Check the area of your repair for unsoldered or poorly soldered

connections. Check the entire board surface for solder splashes and bridges.

2) Check the inter board wiring to ensure that no wires are pinched or

contact  high-wattage resistors.
3)Check  all  control  knobs,  shields,  covers,  ground  straps  and  mounting
hardware  have  been  replaced.  Be  absolutely  certain  you  have  replaced  all
the insulators.
4) Look for unauthorized replacement parts, particularly transistors that
were  installed  during  a  previous  repair.  Point  them  out  to  the  customer  and
recommend their replacement.
5)  Look  for  parts  which,  though  functioning  show  obvious  signs  of
deterioration.  Point  them  out  to  the  customer  and  recommend  their
replacement.
6)  Check  the  line  cords  for  cracks  and  abrasion.  Recommend  the
replacement  of any such line cord to the customer.
7) Check the antenna terminals, metal trim, metalized knobs, screws and all
other exposed metal parts for AC leakage. Check leakage test as described
next.
8.  For  safety  reasons,  repairing  the  Power  board  and/or  Inverter  board  is
prohibited.

Figure 2. AC voltmeter to check AC leakage

Safety Notes

1-3. Caution About the Lithium Battery

1) Danger of explosion if battery is incorrectly replaced. Replace only with
the same or equivalent type.
2) Outer case broken battery should not contact to water.

1-5.Leakage Test

The AC leakage from any exposed metal part to earth ground and from all
exposed metal parts to any exposed metal part having a return to chassis must
not exceed 0.5mA (500 microamperes).
Leakage current can be measured by any one of the three methods:-
1) A commercial leakage tester such as the SIMPSON 229 or RCA WT540A.
Follow the manufacturers instructions to use those instructions.
2) A battery-operated AC milliampmeter The DATA PRECISION 245 digital
multimeter is suitable for this job.

1-6. How to Find a Good Earth Ground

1) A cold-water pipe is a guaranteed earth ground; the cover-plate retaining
screw on most AC outlet boxes is also at earth ground.
2) If the retaining screw is to be used as your earth ground, verify that it is at
ground by measuring the resistance between it and a cold-water pipe with an
ohmmeter. The reading should be zero ohms.
3) If a cold-water pipe is not accessible, connect a 60- to 100-watt trouble-
light (not a neon lamp) between the hot side of the receptacle and the
retaining screw. Try both slots, if necessary, to locate the hot side on the line;
the lamp should light at normal brilliance if the screw is at ground potential
(see Figure 3).