Servicing; Safety And Service Guidelines; Ac Leakage Test; Ac Leakage Voltmeter Circuit - Zenith ZVM-1240 Service Manual

Servicing
This section provides servicing information to assist
in servicing and troubleshooting the monitor. Included
are safety servicing guidelines, cleaning instructions,
adjustments, inspection, testing, and troubleshooting.
Safety and Service Guidelines
WARNING: No work should be attempted on any part
of the chassis by anyone not familiar with Zenith ser-
vice procedures and precautions. Otherwise, personal
injury may result.
WARNING: With the monitor power turned off and dis-
connected, discharge the high voltage anode lead at
the CRT using a jumper lead connected between the
chassis and a screwdriver (See Figure 14). Failure to
comply could result in severe shock and/or personal
injury.
WARNING: Do not operate a monitor with excessive
high voltage because the monitor will produce x-rays
from the CRT when the high voltage is excessive. Al-
ways verify that the high voltage is at the normal level
when servicing the unit.
WARNING: Handle the cathode-ray tube carefully
when you hold, remove, or install it. Otherwise, implo-
sion and/or injury may result.
NOTE: Under no circumstances should the original de-
sign be modified or altered without permission of
Zenith Electronics Corporation.
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A.C. VOLTMETER
(5K OHM/VOLT MINIMUM)
I~I
22-4384
.15uF
AC TVPE
II
rh
II
PLACE THI
ROUND
63-10401-76
ON EACH
PIPE,
TO GOOD EARTH G
SUCH AS WATER
CONDUIT, ETC.
S PROBE
EXPOSED
PART. MET ALLIC
15000
10 WATT
Figure 3
AC Leakage Voltmeter Circuit
AC LEAKAGE TEST
To prevent electrical shock after reassembly, perform
an AC leakage test on all exposed metal parts of the
monitor. Do not use a line isolation transformer to per-
form this test.
1.
2.
Connect the test circuit as shown in Figure 3.
With monitor power turned on, measure the
leakage voltage between earth ground and an
exposed monitor metal part.
3. Repeat the measurement with the meter leads
reversed.
4. Repeat steps 2 and 3 until all exposed monitor
metal parts are verified to have satisfactory AC
leakage levels.
WARNING: Any leakage voltage measurement that
exceeds 0.75 volts rms (0.5 milliamperes AC) consti-
tutes a potential shock hazard and must be corrected.
CAUTION: Some of the integrated circuits (ICs) used
in the monitor are electrostatic-sensitive devices
(ESO). These devices can be damaged by static elec-
tricity. When handling any IC, use a wrist grounding
strap or be sure to equalize the static charge before
touching the IC.