How to enter the service mode, adjustments, troubleshooting, schematic– Using ICs LA76812, LA78040, LA7841, LA7845, LC863232A

Color TVs using LA76812/LA76814/LC863232A-5V57, AT24C04, TDA7056Q, LA78040/LA7841/LA7845, PC817, BSC2433553-6P/BSC25-3355-8/BSC29-3801-13R LOTs

Excessive high voltage can produce potentially hazardous X-ray radiation.
To avoid such hazards, the high voltage must not be above 31.0KV(14") or 35.0KV(21") under any conditions. The normal value of the high voltage of this television is 22.5KV(14") or 26.5KV(21") at max beam current (maximum brightness) under a 90-260V, 50/60HZ AC power source.

Service should not be attempted by anyone unfamiliar with the necessary precautions on this television. The followings are the necessary precautions to be observed before servicing.
1). Since the chassis of this television is directly connected to the AC-power line (HOT chassis), an isolation transformer should be used during any dynamic service to avoid possible shock hazard.
2). Always discharged the picture tube anode to the CRT conductive coating before handing the picture tube. The tube is highly evacuated and, if broken, glass fragments will be violently expelled. Use shatterproof goggles and keep picture tube away from the body while handing.
3). When replacing a chassis in the cabinet, it always is certain that all the protective devices are put back in place, such as non-metallic control knobs, insulating covers, shields isolation resistor-capacitor network, etc

4). Before returning the set to the customer, always perform an AC leakage current check on the exposed metallic parts of the cabinet such as terminals, screws, metal overlays control shafts, etc., to insure that the set is safe to operate without danger of electrical shock.

Many electrical parts in this chassis have special safety-related characteristics. These characteristics are often passed unnoticed by a visual inspection and the protection afforded by them cannot necessarily be obtained by using replacement, rated for higher voltage, wattage, etc.  Replacement parts with special safety characteristics must be replaced with the same number. The use of substitute replacement parts that do not have the same safety characteristics as specified in the parts list may create shock, fire, X-ray radiation of other hazards.

Automatic Degaussing

A degaussing coil is mounted around the picture tube, so that external degaussing after mobbing the TV should be unnecessary. But the receiver must be properly degaussed upon installation. The degaussing coil operates for about 1 second after the power is switched ON. If the set is moved or turned in a different direction, the power should be OFF for at least 15 minutes. If the chassis or parts of the cabinet become magnetized, poor color purity will result. If this happens, use an external degaussing coil. Slowly move the degaussing coil around the faceplate of the picture tube, the sides and the front of it, slowly withdraw the coil to a distance of about 6 feet before turning power OFF.

Method of access to the service mode

Using the remote control performs the following steps:

1. Press the RECALL key on the remote control and the volume key minus (V-) on the TV at the same time. The service mode screen will appear on the screen of the TV the word FACTORY, indicating that it is in mode of service.

2. To enter the B / W mode (white balance) flies to press RECALL on the remote control and volume less on the TV at Same time

3. For color adjustments, vertical, press RECALL again the remote control and volume less on the TV at the same time

4. To return to the original TV position press the KEY RETURT on the remote control and turn off the TV. ".

Line Mode

After being in service mode, you can RGB bias, pressed "0" to decrease "S-BRI"; pressing "1" to increase "S-BRI".

Pressing "2" to decrease "R-BIA"; pressing "3" to increase "R-BIA". Pressing "4" to decrease "G-BIA";

pressing "5" to increase "G-BIA". Pressing "6" to decrease "B-BIA"; press "7" to increase "B-BIA".

B / W Balance Adjusts

After setting RGB bias to, press "Mute" to return to the mode

"B / W BALANCE", then press CH + or CH- to select the items in the "B / W BALANCE" table, press VOL + or VOL- to select the items.

ADJUST Mode (Preset related to tube used)

En el modo "ADJUST", ud puede ajustar size, picture position, sub picture status, OSD position, AGC status etc. , press CH+ or CH- to select items in the " ADJUST " Table, press VOL+ or VOL- to adjust selected item.

SETUP Mode

In the "SETUP" mode, you can select the options, AV / TV option, OSD option, power ON / OFF option etc. , press CH + or CH to select the items in the "SETUP" table, pressing VOL + or VOL- to select the settings.

Troubleshooting

No grating, no picture, no sound

General, these failures are produced by power sources, because of which refer to a wider area, so that can be divided them two conditions to explain: no +B 110 V and existing +B 110V.
(1) No +B (110V) voltage (voltage of network AC 90～ 260V ) These failures may be caused by power supply switch.

Existing +B 110 V
These failures may be caused by abnormal operation of horizontal scan, to confirm which can observe the filament of tube whether bright on.
If determined horizontal scan in abnormal operation, look for the failure start from the horizontal drive stage. Search upward to LA76812 with method of checking DC voltage and waveform according to sequence: PIN27/H.OUT port→ PIN25 power supply→VD622 output

Existing grating and no picture
Because of the picture video signals and OSD characters display are input from PIN44, PIN15, PIN16, PIN17 of LA76812(N201), so to observe characters on screen of faulted TV can determine the approximate area of fault.

Existing grating, no picture and sound
Processing according Existing grating and no picture” at first, let the picture display normally, then check sound.

CPU non-operating

This chassis is consisted of main chip LA76812 controlled by Sanyo I2C bus and CPU LC863232A.
LA76812 is a performance and quality IC including PIF, SIF, AFC, V/C/D, etc circuits.
TDA7056B used in BTSC sound system is a power amplifier.
CXA2104S is a BTSC decode function IC.
LA4225A used in MONO sound system is another power amplifier
LA78040 is used for vertical power amplifier