Toshiba 27A50, Service Manual

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GENERAL ADJUSTMENTS
SPECIFIC INFORMATIONS
CHAPTER 1 GENERAL ADJUSTMENTS
SAFETY INSTRUCTIONS
WARNING: BEFORE SERVICING THIS CHASSIS, READ THE “X-RAY RADIATION PRECAUTION”, “SAFETY PRECAU-
TION” AND “PRODUCT SAFETY NOTICE” INSTRUCTIONS BELOW.
X-RAY RADIATION PRECAUTION
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 17.)
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.
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. 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:
AC VOLTMETER
0.15
µ
F
Good earth ground
such as a water
pipe, conduit, etc.
Place this probe on
each exposed
metallic part.
1500 ohm
10 watt
PRODUCT SAFETY NOTICE
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.