Zenith ZVM-121 Service Manual page 4

Page 1.-2
7. After you reassemble the set, always perform an
AC leakage test on all exposed metallic parts of
the cabinet to be sure the set is safe to operate
without danger of electrical shock. DO NOT
USE A LINE ISOLATION TRANSFORMER
DURING THIS TEST. Use an AC voltmeter with
a 5000 ohms per volt or more sensitivity in the
following manner: Connect a 1500 ohm, 10-watt
resistor (63-10401-76), paralleled by a 0.15
p,F,
150 VAC type capacitor (22-4384), between a
A. C.
VOLTMETER
known good earth ground (water pipe, conduit,
etc.) and the exposed metallic parts, one at a
time. Measure the AC voltage across the combi-
nation 1500 ohm resistor and 0.15 p,F capacitor.
Reverse the AC plug and repeat AC voltage mea-
surements for each exposed metallic part. Volt-
age measured must not exceed 0.75 volts rms.
This corresponds to 0.5 milliamps AC. Any
value exceeding this limit constitutes a poten-
tial shock hazard and must be corrected im-
mediately.
Icpl
22-4384
•
15~F
A. C. TYPE
TO GOOD EARTH GROUND ,--_63_-_1~04",0,-1_-7_6~
SUCH AS WATER PIPE, 1500Q
CONDU IT, ETC. 10 WATT
Figure 1-1
IMPLOSION PROTECTION
1.
All Zenith picture tubes are equipped with an
integral implosion protection system, but be
careful to avoid damage during installation.
Avoid scratching the tube.
2. Use only Zenith replacement tubes.
X-RADIATION
PLACE TH I S PRO BE
ON EACH EXPOSED
METALLIC PART.
tube does not emit X-rays when the HV is at the
factory-specified level.
It
is only when the HV is
excessive that X-radiation can be generated. The
basic precaution which must be exercised is to
keep the HV at the factory-recommended level.
Refer to the X-Ray Precaution Label which is
located inside each Monitor for the correct high
voltage. The proper value is also given in the
applicable service manual. Operation at higher
voltages may cause a failure of the CRT or high
voltage supply and, under certain cir-
cumstances, may produce radiation in excess of
desirable levels.
1.
Be sure procedures and instructions to all ser-
vice personnel cover the subject of X-radiation.
The only potential source of X-rays in the cur-
rent Monitor is the picture tube. However, this
2. Use only Zenith specified CRT anode connec-
tors.