RB2G
CHASSIS
W580B/W585B/W590B/W600B/W605B/W607B/W608B/WM15B
6
3) Measuring the voltage drop across a resistor by means of a VOM or battery
operated AC voltmeter. The 'limit' indication is 0.75V 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 multimeter that have a 2 VAC range are suitable.
(see Figure 2.)
1-4. 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 inter board wiring to ensure that no wires are pinched or
contact high-wattage resistors.
3)Check all control knobs, shields, covers, ground straps and mounting
hardware have been replaced. Be absolutely certain 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, metalized knobs, screws and all
other exposed metal parts for AC leakage. Check leakage test as described
next.
8. For safety reasons, repairing the Power board and/or Inverter board is
prohibited.
Figure 2. AC voltmeter to check AC leakage
Safety Notes
1-3. Caution About the Lithium Battery
1) Danger of explosion if battery is incorrectly replaced. Replace only with
the same or equivalent type.
2) Outer case broken battery should not contact to water.
1-5.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 0.5mA (500 microamperes).
Leakage current can be measured by any one of the three methods:-
1) A commercial leakage tester such as the SIMPSON 229 or RCA WT540A.
Follow the manufacturers instructions to use those instructions.
2) A battery-operated AC milliampmeter The DATA PRECISION 245 digital
multimeter is suitable for this job.
1-6. How to Find a Good Earth Ground
1) A cold-water pipe is a guaranteed earth ground; the cover-plate retaining
screw on most AC outlet boxes is also at earth ground.
2) 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.
3) 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 3).
Figure 3. Checking for earth
ground.
