Akai 21CTU93BC Service Manual download pdf (Page 8)

SAFETY PRECAUTIONS

1. The design of this product contains special hardware, many

circuits and components specially for safety purposes. For

continued protection, no changes should be made to the

original design unless authorized in writing by the

manufacturer. Replacement parts must be identical to those

used in the original circuits. Service should be performed by

qualified personnel only.

2. Alterations of the design or circuitry of the products should

not be made. Any design alterations or additions will void

the manufacturer’s warranty and will further relieve the

manufacturer of responsibility for personal injury or property

damage resulting therefrom.

3. Many electrical and mechanical parts in the products have

special safety-related characteristics. These characteristics

are often not evident from visual inspection nor can the

protection afforded by them necessarily be obtained by

using replacement components rated for higher voltage,

wattage, etc. Replacement parts which have these special

safety characteristics are identified in the parts list of

Service manual. Electrical components having such

features are identified by shading on the schematics

and by ( ！ ) on the parts list in Service manual. The use

of a substitute replacement which does not have the same

safety characteristics as the recommended replacement

part shown in the parts list of Service manual may cause

shock, fire, or other hazards

4. Don’t short between the LIVE side ground and

ISOLATED (NEUTRAL) side ground or EARTH side

ground when repairing. Some model’s power circuit is

partly different in the GND. The difference of the GND is

shown by the LIVE: ( ) side GND, ISOLATED (NEUTRAL) :

( ) side GND and EARTH : ( ) side GND. Don’t short

between the LIVE side GND and ISOLATED (NEUTRAL)

side GND or EARTH side GND and never measure with a

measuring apparatus (oscilloscope etc.) the LIVE side GND

and ISOLATED (NEUTRAL) side GND or EARTH side GND

at the same time. If above note will not be kept, a fuse or

any parts will be broken.

5. If any repair has been made to the chassis, it is

recommended that the B1 setting should be checked or

adjusted (See ADJUSTMENT OF B1 POWER SUPPLY).

6. The high voltage applied to the picture tube must conform

with that specified in Service manual. Excessive high

voltage can cause an increase in X-Ray emission, arcing

and possible component damage, therefore operation under

excessive high voltage conditions should be kept to a

minimum, or should be prevented. If severe arcing occurs,

remove the AC power immediately and determine the cause

by visual inspection (incorrect installation, cracked or melted

high voltage harness, poor soldering, etc.). To maintain the

proper minimum level of soft X-Ray emission, components

in the high voltage circuitry including the picture tube must

be the exact replacements or alternatives approved by the

manufacturer of the complete product.

7. Do not check high voltage by drawing an arc. Use a high

voltage meter or a high voltage probe with a VTVM.

Discharge the picture tube before attempting meter

connection, by connecting a clip lead to the ground frame

and connecting the other end of the lead through a 10kΩ

2W resitor to the anode button.

8. When service is required, observe the original lead dress.

Extra precaution should be given to assure correct lead

dress in the high voltage circuit area. Where a short circuit

has occurred, those components that indicate evidence of

overheating should be replaced. Always use the

9. manufacturer’s replacement components.

10. Isolation Check

(Safety for Electrical Shock Hazard)

After re-assembling the product, always perform an isolation

check on the exposed metal parts of the cabinet (antenna

terminals, video/audio input and output terminals, Control

knobs, metal cabinet, screwheads, earphone jack, control

shafts, etc.) to be sure the product is safe to operate without

danger of electrical shock.

11. The surface of the TV screen is coated with a thin film which

can easily be damaged. Be very careful with it when handle

the TV. Should the TV screen become soiled, wipe it with a

soft dry cloth. Never rub it forcefully. Never use any cleaner

or detergent on it.

(1) Dielectric Strength Test

The isolation between the AC primary circuit and all metal

parts exposed to the user, particularly any exposed metal

part having a return path to the chassis should withstand a

voltage of 3000V AC (r.m.s.) for a period of one second.

(…Withstand a voltage of 1100V AC (r.m.s.) to an appliance

rated up to 120V, and 3000V AC (r.m.s.) to an appliance

rated 200V or more, for a periode of one second.)

This method of test requires a test equipment not generally

found in the service trade.

(2) Leakage Current Check

Plug the AC line cord directly into the AC outlet (do not use

a line isolation transformer during this check.). Using a

“Leakage Current Tester”, measure the leakage current

from each exposed metal part of the cabinet, particularly

any exposed metal part having a return path to the chassis,

to a known good earth ground (water pipe, etc.). Any

leakage current must not exceed 0.5mA AC (r.m.s.).

However, in tropical area, this must not exceed 0.2mA AC

(r.m.s.).

●Alternate Check Method

Plug the AC line cord directly into the AC outlet ( do not use

a line isolation transformer during this check.). Use an AC

voltmeter having 1000 ohms per volt or more sensitivity in

the following manner. Connect a 1500 Ω 10W resistor

paralleled by a 0.15 μ F AC-type capacitor between an

exposed metal part and a known good earth ground (water

pipe, etc.). Measure the AC voltage across the resistor with

the AC voltmeter. Move the resistor connection to each

exposed metal part, particularly any exposed metal part

having a return path to the chassis, and measure the AC

voltage across the resistor. Now, reverse the plug in the AC

outlet and repeat each measurement. Any voltage

measured must not exceed 0.75V AC (r.m.s.). This

corresponds to 0.5mA AC (r.m.s.).

However, in tropical area, this must not exceed 0.3V AC

(r.m.s.).

This corresponds to 0.2mA AC (r.m.s.)

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Akai 21CTU93BC Service Manual Page 8

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