Memorex MT-1132, Service Manual

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IMPORTANT SERVICE SAFETY INFORMATION
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Operation of receiver outside of cabinet or with back removed
involves a shock hazard. Work on these models should only be
performed by those who are thoroughly familiar with
precautions necessary when working on high voltage
equipment.
Exercise care when servicing this chassis with power applied.
Many B plus and high voltage RF terminals are exposed which,
if carelessly contacted, can cause serious shock or result in
damage to the chassis. Maintain connecting ground lead
connections between chassis, escutcheon, picture tube dag
and tuner cluster when operating chassis.
These receivers have a “Polarized” AC line cord. The AC plug is
designed to fit into standard AC outlets in one direction only. The
wide blade connects to the “ground side” and the narrow blade
connects to the “hot side” of the AC line. This assures that the
TV receiver is properly grounded to the house wiring. If an
extension cord must be used, make sure it is of the “polarized”
type.
When it is necessary to make measurements or tests with AC
power applied to the receiver chassis, an Isolation Transformer
must be used as a safety precaution and to prevent possible
damage to transistors. The Isolation Transformer should be
connected between the TV line cord plug and the AC power
outlet.
Certain HV failures can increase X-ray radiation. Receivers
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 25 kV
1.0kV at zero beam current with a line voltage of 120V AC.
Higher voltage may also increase possibility of failure in HV
supply.
It is important to maintain specified values of all components in
the horizontal and high voltage circuits and anywhere else in
the receiver that could cause a rise in high voltage, or operating
supply voltages. No changes should be made to the original
design of the receiver.
Components shown in the shaded areas on the schematic
diagram or identified by the safety mark in the replacement parts
list should be replaced only with exact Factory recommended
replacement parts. The use of unauthorized substitute parts
may create shock, fire, X-radiation or other hazard.
To determine the presence of high voltage, use an accurate
high impedance HV meter connected between second anode
lead and the CRT dag grounding device. When servicing the
High Voltage System remove static charge from it by connecting
10K ohm resistor in series with an insulated wire (such as a
test probe) between picture tube dag and 2nd anode lead (AC
line cord disconnected from AC supply).
The picture tube used in this receiver employs integral implosion
protection. Replace with 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 voltage completely. Keep others without
shatter-proof goggles away.
When removing springs or spring mounting parts from tuner,
tuner cluster or chassis, shatter-proof goggles must be worn.
Keep others without shatter-proof goggles away.
SAFETY INSPECTION
Before returning the receiver to the user, perform the following
safety checks:
PROTECT YOUR CUSTOMER
1. Inspect all lead dress to make certain that leads are not
pinched or that hardware is not lodged between the chassis and
other metal parts in the receiver.
2. Replace all protective devices such as non-metallic control knobs,
insulating fishpapers, cabinet backs, adjustment and compartment covers
or shields, isolation resistor capacitor 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 having a
return path to the chassis ( antenna, cabinet metal, screw heads,
knobs and/or shafts, escutcheon, etc.) in the following manner.
Plug the AC line cord directly into a 120V AC receptacle. (Do not use an
Isolation Transformer during these checks) All checks must be repeated
with the AC line cord plug connection reversed. (If necessary, a non-
polarized adapter plug must be used only for the purpose of completing
these checks.)
If available, measure current using an accurate leakage current tester. (Use
Standard Item No. 25086,21641) Any reading of 0.4 mA or more is
excessive and indicates a potential shock hazard which must be corrected
before returning the receiver to the owner.
If a reliable leakage current tester is not available, this alternate method of
measurement should be used. Using two clip leads, connect a 1500 ohm,
10 watt resistor paralleled by a 0.15 MF capacitor in series with a known
earth ground, such as a water pipe or conduit and the metal part to be
checked. Use a VTVM or VOM with 1000 ohms per volt, or higher
sensitivity to measure this AC voltage drop across the resistor. Any
reading of 0.61 volt RMS or more is excessive and indicates a potential
shock hazard which must be corrected before returning the receiver to the
owner.
AC
VOLTMETER
1500 OHMS
0.15 uF
TO EXPOSED
METAL PARTS
TEST
PROBE
TO KNOWN
EARTH GROUND
X-RAY PROTECTOR CIRCUIT CHECK
PERFORM WHENEVER HIGH VOLTAGE CIRCUITRY OR POWER SUPPLY
CIRCUITRY IS SERVICED.
1. Plug the AC Line Cord (P1) into a AC 120V, 60Hz receptacle.
2. Turn the Power Switch (S101) on and wait for about 10 minutes.
3. Connect the antenna leads to the EXT. Antenna Terminal (TE1)
and select a broadcasting station.
4. Connect DC Digital Voltmeter to TP11 (positive lead) and TP4
(negative lead).
5. Apply DC 11V between TP11 and TP4 from external equipment.
6. If picture and sound do not disappear, check IC301,D552,D553,
D554,R554,R555,R556,R557,C555 and C556.
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