KE-MR50M2 (CH) 3
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-sol-
dered 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 cer-
tain that you have replaced all the insulators.
4. Look for unauthorized replacement parts, particularly transis-
tors, 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 recom-
mend 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 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” indica-
tion is 0.75 V, so analog meters must have an accurate low-
voltage scale. The Simpson 250 and Sanwa SH-63Trd are ex-
amples of a passive VOMs that are suitable. Nearly all battery
operated digital multimeters that have a 2 V AC range are suit-
able. (See Fig. A)
Fig. A. Using an AC voltmeter to check AC leakage.
1.5 k
Ω
0.15
µ
F
AC
Voltmeter
(0.75 V)
To Exposed Metal
Parts on Set
Earth Ground
WARNING!!
SAFETY-RELATED COMPONENT WARNING!!
COMPONENTS IDENTIFIED BY SHADING AND MARK
!
ON THE SCHEMATIC DIAGRAMS, EXPLODED VIEWS
AND IN THE PARTS LIST ARE CRITICAL FOR SAFE
OPERATION. REPLACE THESE COMPONENTS WITH
SONY PARTS WHOSE PART NUMBERS APPEAR AS
SHOWN IN THIS MANUAL OR IN SUPPLEMENTS PUB-
LISHED BY SONY. CIRCUIT ADJUSTMENTS THAT ARE
CRITICAL FOR SAFE OPERATION ARE IDENTIFIED IN
THIS MANUAL. FOLLOW THESE PROCEDURES WHEN-
EVER CRITICAL COMPONENTS ARE REPLACED OR
IMPROPER OPERATION IS SUSPECTED.
AVERTISSEMENT!!
ATTENTION AUX COMPOSANTS RELATIFS À LA
SÉCURITÉ!!
LES COMPOSANTS IDENTIFIÉS PAR UNE TRAME ET
UNE MARQUE ! SONT CRITIQUES POUR LA
SÉCURITÉ. NE LES REMPLACER QUE PAR UNE
PIÈCE PORTANT LE NUMÉRO SPECIFIÉ. LES
RÉGLAGES DE CIRCUIT DONT L’IMPORTANCE EST
CRITIQUE POUR LA SÉCURITÉ DU
FONCTIONNEMENT SONT IDENTIFIÉS DANS LE
PRÉSENT MANUEL. SUIVRE CES PROCÉDURES
LORS DE CHAQUE REMPLACEMENT DE
COMPOSANTS CRITIQUES, OU LORSQU’UN MAUVAIS
FONCTIONNEMENT EST SUSPECTÉ.
