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Extracted text from sony mds jb 940 service manual (Ocr-read)
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After correcting the original service problem, perform the
following safety checks before releasing the set to the customer:
Check the antenna terminals, metal trim, metallized knobs, screws,
and all other exposed metal parts for AC leakage. Check leakage as
described below.
LEAKAGE
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 analog meters must have an accurate low-voltage
scale. The Simpson 250 and Sanwa SH-63Trd are examples of
a passive VOM that is suitable. Nearly all battery operated
digital multimeters that have a 2V AC range are suitable. (See
Fig. A)
SAFETY CHECK-OUT
To Exposed Metal
Parts on Set
0.15 µF
1.5 k-„¦AC
Voltmeter
(0.75 V)
Earth Ground
Fig. A. Using an AC voltmeter to check AC leakage.
TABLE OF CONTENTS
MODEL IDENTIFICATION
- BACK PANEL -
Model
AEP, UK models
Canadian model
US model
Part No.
4-228-507-0s
4-228-507-1s
4-228-507-2s
Par t No.
SELF-DIAGNOSIS FUNCTION ········································4
1. SERVICE NOTE ·······························································6
2. GENERAL ········································································11
3. DISASSEMBLY ······························································14
4. TEST MODE ···································································17
5. ELECTRICAL ADJUSTMENTS ······························22
6. DIAGRAMS
6-1. Block Diagram MAIN Section································31
6-2. Block Diagram DISPLAY/POWER Section···········32
6-3. Note for Printed Wiring Boards and
Schematic Diagrams····················································33
6-4. Circuit Board Location················································33
6-5. Waveforms···································································34
6-6. Printed Wiring Board BD Board·····························35
6-7. Schematic Diagram BD Board (1/2)·······················36
6-8. Schematic Diagram BD Board (2/2)·······················37
6-9. Printed Wiring Board HP Board/KEY Board··········38
6-10. Schematic Diagram HP Board/KEY Board············38
6-11. Schematic Diagram MAIN Board (1/3)··················39
6-12. Schematic Diagram MAIN Board (2/3)··················40
6-13. Schematic Diagram MAIN Board (3/3)··················41
6-14. Printed Wiring Board MAIN Board (Side A)··········42
6-15. Printed Wiring Board MAIN Board (Side B)··········43
6-16. Printed Wiring Board PANEL Section····················44
6-17. Schematic Diagram PANEL Section·······················45
6-18. Schematic Diagram AC Board································46
6-19. Printed Wiring Board AC Board······························47
6-20. IC Block Diagrams······················································48
6-21. IC Pin Function Description········································53
7. EXPLODED VIEWS ······················································60
8. ELECTRICAL PARTS LIST ·······································64
