Emerson MD1777, Service Manual

Page: 2 / 32

• Safety Check after Servicing
Examine the area surrounding the repaired location for damage or deterioration. Observe that screws, parts and wires
have been returned to original positions. Afterwards, perform the following tests and confirm the specified values in
order to verify compliance with safety standards.
1. Insulation resistance test
Confirm the specified insulation resistance or greater between power cord plug prongs and externally exposed parts
of the set (RF terminals, antenna terminals, video and audio input and output terminals, microphone jacks, earphone
jacks, etc.). See table below.
2. Dielectric strength test
Confirm specified dielectric strength or greater between power cord plug prongs and exposed accessible parts of the
set (RF terminals, antenna terminals, video and audio input and output terminals, microphone jacks, earphone jacks,
etc.) See table below.
3. Clearance distance
When replacing primary circuit components, confirm
specified clearance distance (d), (d') between soldered
terminals, and between terminals and surrounding
metalic parts. See table below.
Table 1: Rating for selected areas
* Class II model only.
Note: This table is unofficial and for reference only. Be sure to confirm the precise values for your particular country
and locality.
4. Leakage current test
Confirm specified or lower leakage current between B (earth ground, power cord plug prongs) and externally
exposed accessible parts (RF terminals, antenna terminals, video and audio input and output terminals, microphone
jacks, earphone jacks, etc.)
Measuring Method: (Power ON)
Insert load Z between B (earth ground, power cord plug
prongs) and exposed accessible parts. Use and AC
voltmeter to measure across both terminals of load Z.
See figure and following table.
Table 2: Leakage current ratings for selected areas
Note: This table unofficial and for reference only. Be sure to confirm the precise values for your particular country and
locality.
Z
Exposed
accessible
part
AC Voltmeter
(high impedance)
Earth Ground
power cord plug prongs
B
Fig. 2
AC Line Voltage Region
Insulation Dielectric Clearance
Resistance Strength Distance (d), (d')
100V Japan
≥
1 M
Ω
/500 V DC 1kV 1 minute
≥
3 mm
110 to 130V
USA &
– – –
900V 1 minute
≥
3.2mm
Canada
* 110 to 130 V Europe
≥
10 M
Ω
/500 V DC 4 kV 1 minute
≥
6 mm (d)
200 to 240 V Australia
≥
8 mm (d')
(a: Power cord)
Fig. 1
d
Primary circuit terminals
Chassis
d'
a
AC Line Voltage Region
Earth Ground
Load Z Leakage Current (i)
(B) to:
100V Japan ¡
≤
1m A rms
Exposed accessible
parts
110 to 130 V
USA &
¡
≤
0.5 m A rms
Exposed accessible
Canada parts
¡
≤
0.7 m A peak Antenna earth
110 to 130 V Europe ¡
≤
2 m A dc terminals
200 to 240 V Australia ¡
≤
0.7 m A peak
Other terminals
¡
≤
2 m A dc
1k
1.5k
1.5kµF
2k
50k