AZ3TK
AZ3TK 6
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 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 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”.
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
