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.
4776
SET 4776
GridTrace Location
High Voltage Shutdown Test .................. 1
IC Functions ........................................... 2
Important Parts Information ................... 4
Miscellaneous Adjustments ................... 1
Parts List ................................................. 4
Momentarily short BC14901 (see Q14901 base) to ground. The receiver should lose raster and sound. If
receiver does not lose raster and sound, the shutdown circuit should be repaired. To resume normal
operation, remove AC power for approximately 30 seconds and then turn the receiver on.
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.
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
EquipmentSencore No.
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
NOTE: VHF Low Band voltages taken on channel 2.
VHF High Band voltages taken on channel 7.
UHF Band voltages taken on channel 14.
Q17404
E12.0V12.0V12.0V
B11.8V11.7V0V
C.5V.6V11.4V
Page 3
MISCELLANEOUS ADJUSTMENTS
SET 4776 Page 1
NOTE: All procedures require an antenna connected and power applied to the set.
HIGH VOLTAGE CHECK
Tune in a picture. Set brightness, contrast, and color to minimum. Connect a high
voltage probe to the CRT anode. High voltage should measure 26kV to 28kV.
COLOR TEMPERATURE
NOTE: See Service Adjustment Parameters to change drive and bias values.
Press menu button for collapsed raster service line. Disconnect the antenna. Preset
the red, green, and blue drive values to 32. Adjust screen control for a service line
that is just visible. Adjust red, green, and blue drives to obtain a white raster. Check
the low light to high light gray scale tracking. Repeat the procedure, if necessary, to
obtain the best performance
SERVICE MENU
The following adjustment procedures are accessed thru a service menu. To access the service menu, turn the receiver on, press the menu button and hold it down while
pressing the power button. While holding down the menu button, release the power button and press the volume + button. The screen will display a one line menu, on the
left the parameter P0, and on the right the value of that parameter V0. Release buttons. Adjustments are made by selecting the proper parameter and changing the value of
that parameter. To change the parameter number use channel up and down buttons. To adjust the current value of that parameter use volume + and - buttons. To access and
change any of the adjustments, the proper parameter pass number must be entered. This information is listed at the beginning of the alignment. When these parameters are
modified, the T-Chip and the corresponding EEPROM are updated. All service adjustments are bus controlled, except focus and screen.
NOTE: In order to adjust the RF AGC, audio or video levels, tuner, PIP, or stereo circuits, the ChipperCheck hardware and software must be used. This can be purchased
from Thomson Electronics. Before making any changes to any of the values, record the On Set values.
SERVICE ADJUSTMENT PARAMETERS
No.Parameter NameValueRangeComment
0Pass number for serviceMust set to 76-May not advance until value is set to 76.
1Error Code 100 - 255Displays the first error detected. Set to 0 before exiting.
2Error Code 200 - 255Displays the second error detected. Set to 0 before exiting.
3Error Code 300 - 255Displays the last error detected. Set to 0 before exiting.
4Horizontal Phase100 - 15Tune in a crosshatch pattern, adjust to center the pattern on the screen.
5EW DC (Width)160 - 31Tune in a crosshatch pattern, adjust for slight horizontal overscan.
6EW Amplitude80 - 15Set value to 8.
7EW Tilt80 - 15Set value to 8.
8Top Corner Pin Correction20 - 7Set value to 2.
9Bottom Corner Pin Correction20 - 7Set value to 2.
10Vertical DC330 - 63Tune in a crosshatch pattern, adjust to center vertically.
11Vertical Size840 - 127Tune in a crosshatch pattern, adjust for slight vertical overscan.
12Vertical Countdown Mode00 - 3Set value to 0. (0 = Standard, 1 = Non-Standard, 2 = 50Hz, 3 = 48Hz)
13Red Bias300 - 127Press menu button on the TV set for setup line.
14Green Bias150 - 127Press menu button on the TV set for setup line.
15Blue Bias340 - 127Press menu button on the TV set for setup line.
16Red Drive410 - 6317Green Drive330 - 6318Blue Drive320 - 6319Gemstar Horizontal OSD Position1660 - 255Set value to 166.
20Gemstar Vertical OSD Position680 - 255Set value to 68.
21Gemstar PIP Horizontal Position400 - 255Set value to 40.
22Gemstar PIP Vertical Position430 - 255Set value to 43.
23Gemstar PIP Window Vertical Size30 - 13Set value to 3.
ParameterOn SetValue
adjustment parameters.
See Error Codes Chart.
See Error Codes Chart.
See Error Codes Chart.
ERROR CODES CHART
ERROR CODE
DECHEXError LocationCondition Indicated
000No error code10116.0V fault16.0V STBY source is failing.
30312.0V run fault12.0V source is failing.
404T4 ChipRun supply failed.
808T4 ChipX-ray protection caused high voltage shutdown.
909T4 Chip (POR)Power supply problem at (POR) power on reset.
100AF2 PIP module error (POR)Power supply problem at (POR) power on reset/PIP.
110BStereo decoder (POR)Power supply problem at reset/Stereo decoder.
1610Run IIC Bus held lowRun IIC clock or data held low.
1812Standby IIC Bus held lowStandby IIC clock or data held low.
2317Gemstar 3 BoardGuide fatal error on set using Gemstar 3 Board.
2418Gemstar 3 BoardTask monitor error on set using Gemstar 3 Board.
2519Gemstar 3 BoardWatchdog error on set using Gemstar 3 Board.
261AGemstar 3 BoardTask monitor error on set using Gemstar 3 Board.
3220Gemstar 3 BoardCPU error on set using Gemstar 3 Board.
3422Gemstar 3 BoardGemstar 3 fails to acknowledge.
442CF2 PIP module errorF2PIP fails to acknowledge.
10266Octal DACOctal DAC fails to acknowledge.
12880Stereo decoderStereo decoder fails to acknowledge.
160A0Main or PIP tuner EEPROMMain or PIP tuner EEPROM fails to acknowledge.
186BAT4 ChipT4 Chip fails to acknowledge.
196C4Main tuner PLL/DACMain tuner PLL IC fails to acknowledge.
198C6Main tuner PLL/DACMain tuner DAC IC fails to acknowledge.
ERROR CODES
If certain failures occur, the matching error codes will be stored in the
EEPROM. These error codes will be displayed in parameters 1, 2, and 3.
The first failure error code will be stored at parameter 1 and the second
failure error code will be stored at parameter 2. Parameter 3 will be
updated to display the most recent failure occurred in the chassis. If a
failure of a bus IC occurred, the normal acknowledgment checking of that
bus will be disabled in the service mode and the address of that IC which
failed will be stored in one of the error code parameters. After every repair
is done to the chassis it is recommended to check the error code
parameters, and reset them back to value 0.
SW13201Switch215500Power
SW13202Switch215500Volume Up
SW13203Switch215500Volume Down
SW13204Switch215500Channel Up
SW13205Switch215500Channel Down
SW13206Switch215500Menu
# For SAFETY use only equivalent replacement part.
(1) Bonded part of CRT.
(2) Screen and focus controls are part of T14401.
Important Parts Information
ν Parts not listed in the parts list are
commonly available at your local
electronics parts retailer.
ν The parts listed here are those not
usually available from a well-stocked
supply cabinet or bin.
ν Where items may be replaced with
equivalent parts, several alternates are
shown from participating vendors.
ν On the parts lists, safety items are
marked with a # to remind you that only
exact replacements are recommended
for these items.
ν 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
Or consult the Sams Annual Index for the
address of the original equipment
manufacturer.
Participating Vendors
Information on test equipment and
replacement parts is listed in these pages
for the following participating vendors.
Consult the Sams Annual Index for their
current address.
ν NTE Electronics, Inc. (NTE)
ν Sencore, Inc.
GE MODEL 27GT720TX1 (CHASSIS CTC203AX)
SET 4776 Page 4
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