Arachnid SB31-8U, Руководство по обслуживанию

Страница: 3 / 14

PREFACE
SAFETY INSPECTION
SAFETY PRECAUTIONS
Operation of the monitor outside of its cabinet or
with its back removed introduces a shock hazard.
Service should only be performed by those who
are thoroughly familiar with the precautions
necessarry when working on high voltage
equipment.
Exercise care when servicing this chassis with
power applied. Many voltage and video input
terminals are exposed which, if carelessly contacted,
can cause serious shock or result in damage to the
chassis. Maintain interconnecting earth ground
between the chassis, picture tube (CRT) dag, and
PCB ground when operating the chassis.
Certain High Voltage failures can increase X-ray
radiation. The monitor should not be operated with
HV levels exceeding the specified rating for their
chassis type. The maximum operating HV specified
for the chassis used in these receivers is 12KV +1
and -2KV at zero beam current with a line voltage
of 120VAC. Higher voltage may also increase the
possibility of failure in the HV supply.
It is important to maintain specified values of all
components in the horizontal and HV circuits and
anywhere else in the monitor that could cause a
rise in HV or operating supply voltages. No
changes should be made to the original design of
the monitor.
To determine the presence of high voltage, use an
accurate high impedance, HV meter connected
between the second anode lead and the CRT dag
grounding device. When servicing the High Voltage
System, remove static charge by connecting a 10K
ohm resistor in series with an insulated wire (such
as a test probe) between the CRT dag and the 2nd
anode lead. Do this BEFORE disconnecting the
AC line cord from the AC recepticle.
The picture tube used in this monitor employs
integral implosion protection. Replace with a tube
of the same type number for continued safety. Do
not lift picture tube by the neck. Handle the picture
tube only when wearing shatter-proof goggles and
after discharging the high voltages completely.
Keep others without shatter-proof goggles away.
1. Inspect all wire harness assemblies to make sure
that the wires are not pinched or that nothing is
lodged between the chassis and other metal parts.
2. Replace all protective devices such as non-
metallic control knobs, insulating fishpapers,
cabinet backs, adjustment and compartment
covers or shields, isolation resistor-capacity
networks, mechanical insulators, etc.
3. To be sure that no shock hazard exists, a check
for the presence of leakage current should be
made at each exposed metal part connected to
the chassis, such as cabinet metal, screw heads,
knobs and/or shafts, etc. as follows:
a. Plug the AC line cord into a 12VAC recepticle.
(Do not use an isolation transformer during these
checks.) All checks must be repeated with the
AC line cord plug connections reversed. ( A non-
polarized adaptor plug may be used only for the
purpose of these tests.)
b. Measure the current using an accurate leakage
current tester, if available. (We recommend
Standard Equipment Item # 21641.) Any reading
of 0.46A or more is excessive and indicates a
potential shock hazard which must be corrected.
c. If a reliable leakage current tester is not
available, and alternate method of measurement
should be used. Using two clip leads, connect a
1.5K ohm, 10 watt resistor in parallel with a
0.15uf capacitor; all in series with a known earth
ground. Use a VTVM or VOM with 1000 ohms
per volt or higher sensitivity to measure the AC
drop across the resistor. Any reading of 0.35V
RMS or more is excessive and indicates a
potential shock hazard which must be corrected.
Figure 1, Voltmeter
hookup for safety
check
2