Philips MX975D, Service Manual

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X-RADIATION
1. Be sure procedures and instructions to all your service personnel cover the subject of X-radiation.
Potential sources of X-rays in TV receivers are the picture tube and the high voltage circuits. The basic
precaution which must be exercised is to keep the high voltage at the factory recommended level.
2. To avoid possible exposure to X-radiation and electrical shock, only the manufacturer's specified
anode connectors must be used.
3. It is essential that the service technician has an accurate HV meter available at all times. The
calibration of this meter should be checked periodically against a reference standard.
4. When the HV circuitry is operating properly there is no possibility of an X-radiation problem. High
voltage should always be kept at the manufacturer's rated value - no higher - for optimum performance.
Every time a color set is serviced, the brightness should be run up and down while monitoring the HV
with a meter to be certain that the HV is regulated correctly and does not exceed the specified value.
We suggest that you and your technicians review test procedures so that HV and HV regulation are
always checked as a standard servicing procedure, and the reason for this prudent routine is clearly
understood by everyone. It is important to use an accurate and reliable HV meter. It is recommended
that the HV reading be recorded on each customer's invoice, which will demonstrate a proper concern for
the customer's safety.
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.
LEAKAGE CURRENT COLD CHECK
1. Unplug the ac line cord and connect a jumper between the two prongs of the plug.
2. Turn on the power switch.
3. Measure the resistance value between the jumpered ac plug and all exposed cabinet parts of the
receiver, such as screw heads, antennas, and control shafts. When the exposed metallic part has a
return path to the chassis, the reading should be between 1 megohm and 5.2 megohms. When the
exposed metal does not have a return path to the chassis, the reading must be infinity. Remove the