Philips 55PP9401 Service Manual page 9

d. X-Radiation and High Voltage Limits - Because the picture tube is the primary potential
source of X-radiation in solid-state TV receivers, it is specially constructed to prohibit X-radiation
emissions. For continued X-radiation protection, the replacement picture tube must be the same type
as the original. Also, because the picture tube shields and mounting hardware perform an X-radiation
protection function, they must be correctly in place. High voltage must be measured each time
servicing is performed that involves B+, horizontal deflection or high voltage. Correct operation of the
X-radiation protection circuits also must be reconfirmed each time they are serviced. (X-radiation
protection circuits also may be called "horizontal disable" or "hold down.") Read and apply the high
voltage limits and, if the chassis is so equipped, the X-radiation protection circuit specifications given
on instrument labels and in the Product Safety & X-Radiation Warning note on the service data
chassis schematic. High voltage is maintained within specified limits by close tolerance safety-related
components/adjustments in the high-voltage circuit. If high voltage exceeds specified limits, check
each component specified on the chassis schematic and take corrective action.
2. Read and comply with all caution and safety-related notes on or inside the receiver cabinet, on the
receiver chassis, or on the picture tube.
3. Design Alteration Warning - Do not alter or add to the mechanical or electrical design of this TV
receiver. Design alterations and additions, including, but not limited to circuit modifications and the
addition of items such as auxiliary audio and/or video output connections, might alter the safety
characteristics of this receiver and create a hazard to the user. Any design alterations or additions will
void the manufacturer's warranty and may make you, the servicer, responsible for personal injury or
property damage resulting therefrom.
4. Picture Tube Implosion Protection Warning - The picture tube in this receiver employs integral
implosion protection. For continued implosion protection, replace the picture tube only with one of the
same type number. Do not remove, install, or otherwise handle the picture tube in any manner without
first putting on shatterproof goggles equipped with side shields. People not so equipped must be kept
safely away while picture tubes are handled. Keep the picture tube away from your body. Do not handle
the picture tube by its neck. Some "in-line" picture tubes are equipped with a permanently attached
deflection yoke; because of potential hazard, do not try to remove such "permanently attached" yokes
from the picture tube.
5. Hot Chassis Warning
a. Some TV receiver chassis are electrically connected directly to one conductor of the ac power cord
and may be serviced safely without an isolation transformer only if the ac power plug is inserted so
that the chassis is connected to the ground side of the ac power source. To confirm that the ac
power plug is inserted correctly, with an ac voltmeter, measure between the chassis and a known
earth ground. If a voltage reading in excess of 1.OV is obtained, remove and reinsert the ac power
plug in the opposite polarity and again measure the voltage potential between the chassis and a
known earth ground.
b. Some TV receiver chassis normally have 85Vac (RMS) between chassis and earth ground
regardless of the ac plug polarity. This chassis can be safety-serviced only with an isolation
transformer inserted in the power line between the receiver and the ac power source, for both
personnel and test equipment protection. Some TV receiver chassis have a secondary ground
system in addition to the main chassis ground. This secondary ground system is not isolated from
the ac power line. The two ground systems are electrically separated by insulation material that
must not be defeated or altered.
6. Observe original lead dress. Take extra care to assure correct lead dress in the following areas: a.
near sharp edges, b. near thermally hot parts - be sure that leads and components do not touch