CPD-E240
SAFETY CHECK-OUT
After correcting the original service problem, perform the following Leakage Test
safety checks before releasing the set to the customer: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,
1. Check the area of your repair for unsoldered or poorly soldered must not exceed 0.5 mA (500 microamperes). Leakage current can be
connections. Check the entire board surface for solder splashes and measured by any one of three methods.
bridges.
1. A commercial leakage tester, such as the Simpson 229 or RCA
WT-540A. Follow the manufacturers? instructions to use these
2. Check the interboard wiring to ensure that no wires are ?pinched? or
instructions.
touching high-wattage resistors.
2. A battery-operated AC milliammeter. The Data Precision 245 digital
3. Check that all control knobs, shields, covers, ground straps, and
mounting hardware have been replaced. Be absolutely certain that multimeter is suitable for this job.
you have replaced all the insulators.
3. Measuring the voltage drop across a resistor by means of a VOM
4. Look for unauthorized replacement parts, particularly transistors, or battery-operated AC voltmeter. The ?limit? indication is 0.75
V, so analog meters must have an accurate low voltage scale.
that were installed during a previous repair. Point them out to the
customer and recommend their replacement.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).
5. Look for parts which, though functioning, show obvious signs of
deterioration. Point them out to the customer and recommend their
replacement.
How to Find a Good Earth Ground
A cold-water pipe is a guaranteed earth ground; the cover-plate retaining
6. Check the line cords for cracks and abrasion. Recommend the screw on most AC outlet boxes is also at earth ground. If the retaining
replacement of any such line cord to the customer.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.
7. Check the B+ and HV to see if they are speciŢ ed values. Make sure
your instruments are accurate; be suspicious of your HV meter if
sets always have low HV.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
8. Check the antenna terminals, metal trim, ?metallized? knobs,
line; the lamp should light at normal brilliance if the screw is at ground
screws, and all other exposed metal parts for AC leakage. Check potential (see Figure B).
leakage as described below.
To Exposed Metal
Parts on Set
Trouble Light
Ohmmeter
AC Outlet Box
0.15 ?F1.5 K &AC
Voltmeter
(0.75 V)
Cold Water Pipe
Earth Ground
Figure A. Using an AC voltmeter to check AC leakage.Figure B. Checking for earth ground.
? 6 ? |
ACEC
SONY
