Philips 55PP9401 Service Manual page 17

SERVICING PRECAUTIONS
General Servicing Guidelines
1. Always unplug the instrument AC power cord from the AC power source before:
a. Removing or reinstalling any component, circuit board, module, or any other instrument assembly.
b. Disconnecting or reconnecting any instrument electrical plug or other electrical connection.
c. Connecting a test substitute in parallel with an electrolytic capacitor in the instrument.
d. Discharging the picture tube anode.
CAUTION: A wrong part substitution or incorrect polarity installation of electrolytic capacitors may result
in an explosion hazard.
2. Test high voltage only by measuring it with an appropriate high voltage meter or other voltage
measuring device (DVM, FETVOM, etc.) equipped with a suitable high voltage probe. Do not test
high voltage by drawing an arc. The H.V. Distribution Box has an internal 400MW resistor (bleeder
resistor) connected from the high voltage to ground. After power is removed from the instrument the
high voltage will discharge through the high voltage bleeder resistor. If the tubes have high voltage
after power is removed, then the bleeder resistor is defective or the bleeder ground is disconnected.
3. Discharge the picture tube's anode at any of the R, G, or B outputs on the H.V. Distribution Box only
by (a) first connecting one end of an insulated clip lead to the degaussing or kine aquadag
grounding system shield at the point where the picture tube socket ground lead is connected, and
then (b) touching the other end of the insulated clip lead to the picture tube high voltage distribution
box R, G, or B output, using an insulated handle to avoid personal contact with high voltage.
4. Do not spray chemicals on or near this instrument or any of its assemblies.
5. Unless specified otherwise, clean electrical contracts by applying the following mixture to the
contacts with a pipe cleaner, cotton-tipped stick, or comparable nonabrasive applicator: 10% (by
volume) Acetone and 90% (by volume) isopropyl alcohol (90%-99% strength).
CAUTION: This is a flammable mixture. Unless specified otherwise, lubrication of contacts is not
required.
6. Do not defeat any plug/socket B+ voltage interlocks with which instruments might be equipped.
7. Do not apply AC power to this instrument and/or any of its electrical assemblies unless all solid-
state device heat sinks are correctly installed.
Always connect the test instrument ground lead to the appropriate instrument chassis ground before
connecting the test instrument positive lead. Always remove the test instrument ground lead last.
Use only the specified test fixtures with this instrument.
CAUTION: Do not connect the test fixture ground strap to any heat sink in this instrument.
7618 General Information page 4