Safety Check-Out; Leakage Test; How To Find A Good Earth Ground - Sony TRINITRON KV-27S22 Service Manual

KV-27S22/27S26/27S36/29SD2/29PS2/29RS22/29RS22C/29RS26/29RS26C
SAFETY CHECK-OUT
(US Model only)
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 contact 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 functiomng, 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 B+ and HV to see if they are specified
values Make sure your instruments are accurate,
be suspicious of your HV meter if sets always have
low HV
8 Check the antenna terminals, metal trim, "metallized"
knobs, screws, and all other exposed metal parts for
AC Leakage Check leakage as described below
To Exposed Metal
Parts on Set
AC
Voltmeter
Le
—= Earth Ground
Fig A Using an AC voltmeter to check AC leakage
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 05 mA (500 microampere)
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 milliammeter 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 1s 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
2V AC range are suitable (See Fig A)
HOW TO FIND A GOOD EARTH GROUND
A cold-water pipe 1s guaranteed earth ground, the cover-plate
retaining screw on most AC outlet boxes 1s also at earth ground
If the retainung screw 1s to be used as your earth-ground, verify
that itis at ground by measuring the resistance between it and a
cold-water pipe with an ohmmeter The reading should be zero
ohms Ifa cold-water pipe 1s not accessible, connect a 60-100 watts
trouble hight (not a neon lamp) between the hot side of the re-
ceptacle and the retaimmng screw Try both slots, 1f necessary, to
locate the hot side of the line, the lamp should light at normal
brilliance 1f the screw 1s at ground potential (See Fig B)
Trouble Light
Ohmmeter
@ AC Outlet Box
Coid-water Pipe
Fig B. Checking for earth ground