SDM-S51R - Sony Monitor Service Manual (repair manual). Page 2

SDM-S51R(E)

2

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 con-

nections. 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 mount-

ing hardware have been replaced. Be absolutely certain that youhave
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 dete-

rioration. Point them out to the customer and recommend their replace-
ment.

6. Check the line cords for cracks and abrasion. Recommend the replace-

ment 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 right.

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, such as the Simpson 229 or RCA WT-

540A. Follow the manufacturers’ instructions to use these instruments.

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 is 0.75 V, so ana-
log meters must have an accurate low-voltage scale. The Simpson 250
and Sanwa SH-63Trd are examples of a passive VOMs that are suit-
able. Nearly all battery operated digital multimeters that have a 2 V AC
range are suitable.  (See Fig. A)

Fig. A. Using an AC voltmeter to check AC leakage.

1.5 k Ω

0.15 µF

AC
Voltmeter
(0.75 V)

To Exposed Metal
Parts on Set

Earth Ground