Philips 7629, Service Manual

Page: 7 / 374

5. When troubleshooting and making test measurements in a receiver with a problem of excessive high
voltage, reduce the line voltage by means of a Variac to bring the HV into acceptable limits while
troubleshooting. Do not operate the chassis longer than necessary to locate the cause of the excessive
HV.
6. New picture tubes are specifically designed to withstand higher operating voltages without creating
undesirable X-radiation. It is strongly recommended that any shop test fixture which is to be used
with the new higher voltage chassis be equipped with one of the new type tubes designed for this
service. Addition of a permanently connected HV meter to the shop test fixture is advisable. The
CRT types used in these new sets should never be replaced with any other types, as this may result in
excessive X-radiation.
7. It is essential to use the specified picture tube to avoid a possible X-radiation problem.
8. Most TV receivers contain some type of emergency "Hold Down" circuit to prevent HV from rising
to excessive levels in the presence of a failure mode. These various circuits should be understood by
all technicians servicing them, especially since many hold down circuits are inoperative as long as
the receiver performs normally.
PICTURE TUBE REPLACEMENT
The primary source of X-radiation in this television receiver is the picture tube. The picture tube
utilized in this chassis is specially constructed to limit X-radiation emissions. For continued X-
radiation protection, the replacement tube must be the same type as the original, including suffix letter,
or a Philips approved type.
PARTS REPLACEMENT
Many electrical and mechanical parts in Philips television sets 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. The use of a substitute part which does not have the same safety characteristics as the
Philips recommended replacement part shown in this service manual may create shock, fire, or other
hazards.
PRODUCT SAFETY GUIDELINES FOR ALL PRODUCTS
CAUTION : Do not modify any circuit. Service work should be performed only after you are thoroughly
familiar with all of the following safety checks. Risk of potential hazards and injury to the user increases if
safety checks are not adhered to.
USE A SEPARATE ISOLATION TRANSFORMER FOR THIS UNIT WHEN SERVICING.