Only qualified service technicians who are familiar with safety checks
and guidelines should perform service work. Before replacing parts,
disconnect power source to protect electrostatically sensitive parts. Do
not attempt to modify any circuit unless so recommended by the
manufacturer. When servicing the receiver, use an isolation transformer
between the line cord and power receptacle.
SERVICING THE HIGH VOLTAGE AND CRT
Use EXTREME CAUTION when servicing the high voltage circuits. To
discharge static high voltage, connect a 10K ohms resistor in series with a
test lead between the receiver ground and CRT anode lead. DO NOT lift
the CRT by the neck. Always wear shatterproof goggles when handling
the CRT to protect eyes in case of implosion.
X-RAY RADIATION AND HIGH VOLTAGE LIMITS
Be aware of the instructions and procedures covering X-ray radiation. In
solid-state receivers and monitors, the CRT is the only potential source of
X-rays. Keep an accurate high voltage meter available at all times. Check
meter calibration periodically. Whenever servicing a receiver, check the
high voltage at various brightness levels to be sure it is regulating
properly. Keep high voltage at rated value, NO HIGHER. Excessive high
voltage may cause X-ray radiation or failure of associated components.
DO NOT depend on protection circuits to keep voltage at rated value.
When troubleshooting a receiver with excessive high voltage, avoid close
contact with the CRT. DO NOT operate the receiver longer than
necessary. To locate the cause of excessive high voltage, use a variable
AC transformer to regulate voltage. In present receivers, many electrical
and mechanical components have safety related characteristics which are
not detectable by visual inspection. Such components are identified by a
# on both the schematic and the parts list. For SAFETY, use only
equivalent replacement parts when replacing these components.
GENERAL GUIDELINES
Perform a final SAFETY CHECK before returning receiver to customer.
Check repaired area for poorly soldered connections, and check entire
circuit board for solder splashes. Check board wiring for pinched wires or
wires contacting any high wattage resistors. Check that all control knobs,
shields, covers, grounds, and mounting hardware have been replaced. Be
sure to replace all insulators and restore proper lead dress.
SAFETY CHECKS FIRE AND SHOCK HAZARD
Cold Leakage Checks for Receivers with Isolated Ground
Unplug the AC cord, connect a jumper across the plug prongs, and turn
the power switch on (if applicable). Use an ohmmeter to measure the
resistance between the jumped AC plug and any exposed metal cabinet
parts such as antenna screw heads, control shafts, or handle brackets.
Exposed metal parts with a return path should measure between 1M
ohms and 5.2M ohms. Parts without a return path must measure infinity.
Hot Leakage Current Check
Plug the AC cord directly into an AC outlet. DO NOT use an isolation
transformer. Use a 1500 ohms, 10W resistor in parallel with a .15µF
capacitor to connect between any exposed metal parts on the receiver and
a good earth ground. (See figure below.) Use an AC voltmeter with at
least 5000 ohms per volt sensitivity to measure the voltage across the
resistor. Check all exposed metal parts and measure voltage at each point.
Voltage measurements should not exceed .75VAC, 500µA. Any value
exceeding this limit constitutes a potential shock hazard and must be
corrected. If the AC plug is not polarized, reverse the AC plug and repeat
exposed metal part voltage measurement at each point.
INDEXINDEX
INDEX
INDEXINDEX
SET 5303
GridTrace Location
Main Board ....................................... 3
Comb Filter Board ............................3
Important Parts Information ..................... 4
Miscellaneous Adjustments ..................... 1
Parts List ...................................................4
Power Supply .................................... 2
System Control .................................. 2
Television .......................................... 2
Video Switching/Comb Filter ...........3
Service Mode Chart ................................. 1
Test Equipment.........................................3
Tuner Information ....................................1
5303
Technical Service Data
RCA
Model 27V412T (Chassis M134C)
Representative Model
Essential coverage
for servicing a television receiver...
Schematics
The listing of any available replacement part herein in no case constitutes a recommendation, warranty, or guarantee by
SAMS Technical Publishing, LLC as to the quality and suitability of such replacement part. The numbers of the listed parts
have been compiled from information furnished to SAMS Technical Publishing, LLC by the manufacturers of the specific
type of replacement part listed.
Reproduction or use, without express permission, of editorial or pictorial content, in any manner, is prohibited. No patent
liability is assumed with respect to the use of the information contained herein.
High voltage must not be higher than 31.8kV at any beam current.
X RAY PROTECTION TEST
Tune the set to receive a crosshatch signal. Apply an external power supply
to the positive lead of C249 (observe polarity). Slowly increase the voltage
from the supply. The set must shut down and remain off when the voltage
reaches 30V.
B+
Tune the set to receive a crosshatch signal, set the preset picture mode to
normal, and adjust VR802 for 130V ±0.5V at the positive lead of C422.
RF AGC
The RF AGC is factory preset at the time of manufacture for optimum
operation over a wide range of RF signal input conditions and should not
need readjustment, unless there is cable TV adjacent channel interference
or picture bending or channel 6 color beats because of excessive RF signal
input, this can occur if the receiver is located too close to the transmitting
tower. The signal should be attenuated at the antenna to reduce the signal
to a satisfactory level.
NOTE: Adjusting the RF AGC to extreme limits of its parameters unusually provides a poor signal to noise ratio.
SCREEN
Tune the set to receive a crosshatch signal, set the preset picture mode to
normal and set all of the picture controls (brightness, contrast, etc) to
midrange. Enter the service mode and preset the menu 1 values. Set RC,
GC, and BC to 80, GD and BD to 40. While still in the service mode, press
the input button on the remote and the vertical will collapse. Adjust the
screen control to produce a dim horizontal line on the CRT.
COLOR TEMPERATURE
Test pointDisplay
Adjust:Menu 1 RCRed Cutoff
Menu 1 GCGreen Cutoff
Menu 1 BCBlue Cutoff
Menu 1 GDGreen Drive
Menu 1 BDBlue Drive
Set color picture temperature to normal and set all of the picture controls
(brightness, contrast, etc) to midrange. Tune the set to receive a gray scale
stairstep test pattern. Enter the service mode and adjust the values for
cutoff and drive controls to obtain proper color tracking, no tinting of black
and white and shades of gray, and color temperature is 9300 degrees - X =
284, Y = 299.
SUB BRIGHTNESS
Tune the set to receive a gray scale stairstep signal from the A/V inputs. Set
picture color temperature to normal, Set all of the picture controls
(brightness, contrast, etc) to midrange. Enter the service mode and select
menu 5. Adjust the value of BRTC sub brightness to just light the second
dark bar, making sure the first bar stays black.
Test pointDisplay
Adjust:Menu 3 HPOS6H Position
Menu 3 PARA6H Parabola
Menu 3 TRAP6H Trapazoid
Menu 3 HSIZE6H Size
Menu 3 CNRT6H Corner Top
Menu 3 CNRB6H Corner Bottom
Menu 2 HIGHT6Height
Menu 2 VLIN6Linearity
Menu 2 VP60Vertical Center
Menu 2 VSC6Vert S Correct
NOTE: Confirm correct convergence and purity before adjusting geometry.
Tune the set to receive a circular test pattern to make visual geometry
adjustments. Enter the service mode. Adjust menu 2 and menu 3 values for
the least amount of geometric distortion approximately 7% overscan.
SERVICE MODE
NOTE: Pressing the 1 and input buttons on the remote will shut the set
down if you are in the service mode.
To enter the service mode, press and hold the volume down button on the
set while pressing the info/del button on the remote. Menus 1 thru 10 can
be accessed directly using the remote keypad number buttons. For menu 11
press the 1 and notepad buttons on the remote; menu 12 press the 1 and
caps buttons on the remote; menu 13 press 1 and info/del buttons on the
remote; menu 14 press 1 and sleep buttons on the remote; menu 15 press 1
and calendar buttons on the remote; 16 press 1 and insert buttons on the
remote; menu 17 press 1 and FAV buttons on the remote; menu 18 press 1
and go back buttons on the remote. If any of the service mode menu items
have been adjusted, press the sound button to save the settings, and exit the
service mode.
Test equipment listed by participating manufacturer illustrates
typical or equivalent equipment used by Sams engineers to obtain
measurements. This equipment is compatible with most types used
by field service technicians.
EquipmentSencore No.
OscilloscopeSC3100
Generators
RGBCM2125
Multiburst SignalVG91
Color BarVG91
TV StereoVG91
Digital VOMSC3100
Frequency MeterSC3100
Hi-Voltage ProbeHP200
Accessory ProbesTP212
Isolation TransformerPR570
Capacitance AnalyzerLC102
CRT AnalyzerCR7000
AC Leakage TesterPR570
Inductance AnalyzerLC102
Flyback Yoke TesterTVA92
Field Strength MeterSL753
Transistor TesterTF46
Horizontal AnalyzerHA-2500
Video AnalyzerVG91, TVA92
W601, 02 (2)(3)(4)(5) Speaker27100160mm X 125mm, 16 Ohms
X001Crystal2663158MHz
X201Trap2663184.5MHz
X202Filter2663174.5MHz
X1001Crystal26842318.432MHz
Item No.Function/RatingMfr. Part No.Notes
Z101Filter266319SAW
PC Board (4)270963Comb Filter
PC Board (2)(5)270959CRT
PC Board (3)(4)270964CRT
PC Board (2)(3)(4)(5)270958IR Receiver
PC Board (2)(3)(4)(5)270961Keyboard
PC Board (2)(3)(4)(5)270962Side
PC Board (3)(5)260967Yoke Adapter
Spacers267049Yoke Positioning (3 Used)
Transmitter (2)(3)(4)(5)265714Remote, RCR130TB1
Transmitter (1)(6)270372Remote
# For SAFETY use only equivalent replacement part.
(1) Used in model 27V412T.
(2) Used in model 27V412TYX1.
(3) Used in model 27V412TYX3.
(4) Used in model 27V412TYX5.
(5) Used in model 27V412TYX8.
(6) Used in model 24V412T.
(7) Screen and focus controls are part of T402.
Important Parts Information
n Parts not listed in the parts list are commonly available at your local electronics parts retailer.
n The parts listed here are those not usually available from a well-stocked supply cabinet or bin.
n On the parts lists, safety items are marked with a # to remind you that only exact replacements are recommended for
these items.
n When ordering parts, state the model number, part number, and description.
Obtaining Parts
Many of these parts are available from your local Sams authorized distributor or the manufacturer of the equipment. Call
Sams for the name of your nearest distributor:
800-428-7267
Page 4 SET 5303
Page 16
RCA MODEL 27V412T (CHASSIS M134C)
RCA MODEL 27V412T (CHASSIS M134C)
SET 5303 Page 4
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