Sony GDM-20SHT Service Manual page 3

GDM-20SHT
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-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
certain that you have replaced all the insulators.
4. Look for unauthorized replacement parts, particularly tran-
sistors, 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 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.
O.1SIlF
To Exposed Metal
Parts on Set
1.5 kfl
AC
Voltmeter
(0.75 V)
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 rnA (500 microampers).
Leakage current can be measured by anyone 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
YOM 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
examples of a passive VOMs that are suitable. Nearly all
battery operated digital multimeters that have a 2 V AC
range are suitable. (See Fig. A)
WARNING!!
NEVER TURN ON THE POWER IN A CONDITION IN
WHICH THE DEGAUSS COIL HAS BEEN REMOVED.
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
PUBLISHED BY SONY. CIRCUIT ADJUSTMENTS THAT
ARE CRITICAL FOR SAFE OPERATION ARE IDENTIFIED
IN THIS MANUAL. FOLLOW THESE PROCEDURES
WHENEVER CRITICAL COMPONENTS ARE REPLACED
OR IMPROPER OPERATION IS SUSPECTED.
AVERTISSEMENT!!
NE JAMAIS METTRE SOUS TENSION QUAND LA
BOBINE DE DEMAGNETISATION EST ENLEVEE.
ATIENTION AUX COMPOSANTS RELATIFS
A
LA
SECURITE!!
-=-
Earth Ground
LES COMPOSANTS IDENTIFIES PAR UNE TRAME ET
PAR UNE MARQUE
.&
SUR LES SCHEMAS DE
Fig. A. Using an AC voltmeter to check AC leakage.
PRINCIPE, LES VUES EXPLOSEES ET LES LlSTES DE
PIECES SONT D'UNE IMPORTANCE CRITIQUE POUR LA
SECURITE DU FONCTIONNEMENT. NE LES REM-
PLACER QUE PAR DES COMPOSANTS SONY DONT LE
NUMERO DE PIECE EST INDlQUE DANS LE PRESENT
MANUEL OU DANS DES SUPPLEMENTS PUB LIES PAR
SONY. LES REGLAGES DE CIRCUIT DO NT L'IMPOR-
TANCE EST CRITIQUE POUR LA SECURITE DU
FONCTIONNEMENT SONT IDENTIFIES DANS LE
PRESENT MANUEL. SUIVRE CES PROCEDURES LORS .
.~
DE CHAQUE REMPLACEMENT DE COMPOSANTS
CRITIQUES, OU LORSQU'UN MAUVAIS FONCTIONNE-
MENT EST SUSPECTE.
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