NSZ-GS7/NSZ-GX70 iv
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 interboard wiring to ensure that no wires are “pinched” or
touching high-wattage resistors.
3. Check that all Commander 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 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, “metallized” knobs,
screws, and all other exposed metal parts for AC leakage. Check
leakage as described in “Leakage Test”.
8. For safety reasons, repairing the Power Supply Board and is
prohibited.
9.
Check the B+ voltage to see it is at the values specified.
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 0.5 mA (500 microamperes). Leakage current can be
measured by any one of three methods.
1. A commercial leakage tester.
Follow the manufacturers’ instructions provided with the tester.
2. A battery-operated AC milliammeter.
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. Nearly all
battery-operated digital multimeters that have a 2 VAC range are
suitable. (see Figure A)
To Exposed Metal
Parts on Set
0.15 µF
Earth Ground
AC
Voltmeter
(0.75V)
Figure A. Use an AC voltmeter to check AC leakage.
HOW TO FIND A GOOD EARTH GROUND
The cover-plate retaining screw on most AC outlet boxes is at earth ground.
Verify the AC outlet box retaining screw ground by connecting a 60W to
100W incandescent (not a neon or fluorescent 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)
Figure B. Checking for earth ground.
Trouble Light
AC Outlet Box
