KDL-40Z4500, KDL-46Z4500, KDL-52Z4500 (serv.man2) - Sony TV Service Manual (repair manual). Page 7

– 6 –

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 interboard wiring to ensure that no wires are

“pinched” or touching high-wattage resistors.

3. Check that all control knobs, shields, covers, ground straps,

and mounting hardware have been replaced. Be absolutely
certain that 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

 

recom-

mend 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, “metallized”

 

knobs,

screws, and all other exposed metal parts for AC

 

leakage.

Check leakage as described below.

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 0.5 mA (500
microamperes).
Leakage current can be measured by any one of three methods.

1. A commercial leakage tester, such as the Simpson 229 or

 

RCA

WT-540A. Follow the manufacturers’ instructions to

 

use these

instructions.

2. A battery-operated AC milliampmeter. The Data Precision

 

245

digital multimeter is suitable for this job.

3. Measuring the voltage drop across a resistor by means of a

VOM or battery-operated AC voltmeter. The “limit”

 

indication

is 0.75 V, 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 multimeters that have a 2 VAC range are suitable (see
Figure A).

A cold-water pipe is a guaranteed earth ground; the cover-plate
retaining screw on most AC outlet boxes is also at earth ground.
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.

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 B).

To Exposed Meta l
Parts on  Set

0.15 

∝

F

Earth Ground

AC
Voltmeter

o

o

(0.75V)

Trouble Light

AC Outlet Box

Ohmmeter

Cold-water Pipe

FigureA. Using an AC voltmeter to check AC leakage.

Figure B. Checking for earth ground.