Toshiba 13A20 Service-Handbuch - Seite 6

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CHAPTER 1

GENERAL ADJUSTMENTS

WARNING: BEFORE SERVICING THIS CHASSIS, READ THE "X-RAY RADIATION PRECAUTION", "SAFETY PRECAU-

TION" AND "PRODUCT SAFETY NOTICE" INSTRUCTIONS BELOW.

1. Excessive high voltage can produce potentially hazard-

ous X-RAY RADIATION. To avoid such hazards, the high

voltage must not be above the specified limit. The nominal

value of the high voltage of this receiver is (A) kV at zero

beam current (minimum brightness) under a 120V AC

power source. The high voltage must not, under any cir-

cumstances, exceed (B) kV.

Refer to table-1 for high voltage (A), (B).

(See SETTING & ADJUSTING DATA on page 15)

Each time a receiver requires servicing, the high voltage

should be checked following the HIGH VOLTAGE CHECK

procedure in this manual. It is recommended that the read-

ing of the high voltage be recorded as a part of the service

record. It is important to use an accurate and reliable high

voltage meter.

WARNING : Service should not be attempted by anyone unfa-

miliar with the necessary precautions on this receiver. The fol-

lowing are the necessary precautions to be observed before

servicing this chassis.

1. An isolation Transformer should be connected in the power

line between the receiver and the AC line before any serv-

ice is performed on the receiver.

2. Always discharge the picture tube anode to the CRT con-

ductive coating before handling the picture tube. The pic-

ture tube is highly evacuated and if broken, glass frag-

ments will be violently expelled. Use shatter proof gog-

gles and keep picture tube away from the unprotected body

while handling.

3. When replacing a chassis in the cabinet, always be cer-

tain that all the protective devices are put back in place,

such as; non-metallic control knobs, insulating covers,

shields, isolation resistor-capacitor network etc.

4. Before returning the set to the customer, always perform

an AC leakage current check on the exposed metallic parts

of the cabinet, such as antennas, terminals, screwheads,

metal overlays, control shafts etc. to be sure the set is

safe to operate without danger of electrical shock. Plug

the AC line cord directly into a 120V AC outlet (do not use

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

voltmeter having 5000 ohms per volt or more sensitivity in

the following manner:

Many electrical and mechanical parts in this chassis have special safety-related characteristics. These characteristics are

often passed unnoticed by a visual inspection and the protection afforded by them cannot necessarily be obtained by using

replacement components rated for higher voltage, wattage, etc. Replacement parts which have these special safety char-

acteristics are identified in this manual and its supplements; electrical components having such features are identified by

the international hazard symbols on the schematic diagram and the parts list.

Before replacing any of these components, read the parts list in this manual carefully. The use of substitute replacement

parts which do not have the same safety characteristics as specified in the parts list may create shock, fire, X-ray

radiation or other hazards.

SAFETY INSTRUCTIONS

X-RAY RADIATION PRECAUTION

2. This receiver is equipped with a Fail Safe (FS) circuit which

prevents the receiver from producing an excessively high

voltage even if the B+ voltage increases abnormally. Each

time the receiver is serviced, the FS circuit must be checked

to determine that the circuit is properly functioning, follow-

ing the FS CIRCUIT CHECK procedure in this manual.

3. The only source of X-RAY RADIATION in this TV receiver

is the picture tube. For continued X-RAY RADIATION pro-

tection, the replacement tube must be exactly the same

type tube as specified in the parts list.

4. Some part in this receiver have special safety-related char-

acteristics for X-RAY RADIATION protection. For contin-

ued safety, parts replacement should be undertaken only

after referring to the PRODUCT SAFETY NOTICE below.

SAFETY PRECAUTION

Connect a 1500 ohm 10 watt resistor, paralleled by a 0.15

µF, AC type capacitor, between a known good earth ground

(water pipe, conduit, etc.) and the exposed metallic parts,

one at a time. Measure the AC voltage across the combi-

nation of 1500 ohm resistor and 0.15 µF capacitor. Re-

verse the AC plug at the AC outlet and repeat AC voltage

measurements for each exposed metallic part. Voltage

measured must not exceed 0.3 volts rms. This corresponds

to 0.2 milliamp. AC. Any value exceeding this limit consti-

tutes a potential shock hazard and must be corrected im-

mediately.

Good earth ground

such as a water

pipe, conduit, etc.

PRODUCT SAFETY NOTICE

– 3 –

AC VOLTMETER

0.15µF

Place this probe on

each exposed

metallic part.

1500 ohm

10 watt