TOSHIBA - DLP PROJECTION TV_ 46HM84_52HM84_52HMX84_ SIGNAL PROCESSING

Contn:

     The main signal, either composite or component is sent to IC210.  The TC90A92AFG IC features a built-in 3-line digital comb filter and 3D luma and chroma noise reduction system. The chip embedded with 4-Mbit of internal frame memory includes an integrated digital multi-standard color decoder with picture improvement functions. The output is a digital Y, Cb, Cr output.  The Genesis chip, IC203, processes and formats the signals to a 1920X1080i format. The GM6015 Genesis chip is a video converter that incorporates deinterlacing with scaling and aspect ratio conversions for standard and high definition signals. The output is in 4:2:2 format, basically stating four of the luminance pixels are sampled, two of the R-Y pixels are sampled and two B-Y pixels are sampled.

     IC301 is the Digital Back-End Processor.  The TC90A94TBG is an RGB processor with built in scaling, signal conversion, and high image quality functions. The OSD is incorporated here from the main TV micro as an RGB signal. The output is a digital RGB 30 bit single-phase signal. Power supply source includes 3.3V, 2.5 V and 1.5V. Low Voltage Differential Signal, or LVDS, is used to transfer the signal to the Talen Light Engine at IC311.

TROUBLESHOOTING

     When troubleshooting any video or audio related issues, keep in mind the logical flow of the signal paths. A couple of areas should always be considered; one example would be user settings. It is important to check user settings prior to any troubleshooting. For example, the speakers could be set to the “off” or external position causing a perceived no audio condition or video inputs could be locked or blocked resulting in a no video condition. Another area is simple A/V connections to the unit. These problems can range from defective A/V cables to simply having the incorrect connection. Ever had a hum from a unit to find the video signal is connected to one of the audio input channels?

VIDEO 

     When troubleshooting any video or audio related issues, keep in mind the logical flow of the signal paths. A couple of areas should always be considered; one example would be user settings. It is important to check user settings prior to any troubleshooting. For example, the speakers could be set to the “off” or external position causing a perceived no audio condition or video inputs could be locked or blocked resulting in a no video condition. Another area is simple A/V connections to the unit. These problems can range from defective A/V cables to simply having the incorrect connection. Ever had a hum from a unit to find the video signal is connected to one of the audio input channels?

     Once  have determined a signal loss, always check other available inputs.  This technique of troubleshooting will help identify the board or circuit causing the problem.

     Once have narrowed the search down to one, or multiple, inputs, it is recommended to input a source video or audio signal you are familiar with.

This is where logic and simple troubleshooting procedures should be taken into account, assuming there are not any error codes from the front LED indicators.  If the lamp were not working, this would definitely cause a no picture condition.

     The next item would be if the TV has an OSD (On-Screen Display). This would have been apparent when verifying the user settings. If the OSD is present, at least the DPEB/GHyper/ Signal Board is sending an output to the light engine.

     Check the DBEP/G-Hyper/Signal inputs. Figure below shows the schematic cut away of the connector PJ16. The circled numbers represent the signal troubleshooting area and figure 10 shows the waveform viewed with an oscilloscope. A signal here will indicate the problem is before to the DBEP/G-Hyper/Signal Board. Using the supplied diagrams and circuit schematics, one could logically pin point the trouble area.

LIGHT ENGINE

     Service Tip - White Lines in Picture: For uniform vertical white lines (about 1 inch a part) extending from the top and bottom of the screen, as shown in Figure.  A red raster is shown in the figure for photographic reasons. However, the lines are very noticeable while viewing a normal picture. Notice the on screen display (OSD) is good, but the lines still appear within the OSD. To the right of the letters CWDL, the lines break up where a letter would be.

     TIP:  With the quick restart feature “on”, the unit will be in a restart standby mode for 5 to 6 minutes. During this restart standby time, the lamp wattage is reduced to 30% and the front green LED lamp will flash. This indication of the LED is to confirm the unit is in the restart standby mode. In a dark room, the picture will appear to have an after glow effect. This can be used to your advantage for troubleshooting. If a picture defect is present and you suspect the problem to be the light engine, you should see the same defect during the restart standby time. Basically, the only circuit in operation will be the light engine.  Again, the TV must be in a very dark environment to achieve this type of evaluation.

     Consider the example of the “white lines in picture”. These lines would be apparent during the restart standby time.

AUDIO

     In the case of no audio and having checked the user settings, go directly to audio amplifier (IC601) and check for inputs and outputs along with voltage supplies.  High wattage areas are always a good starting point. Shown in Figure  are the pin connections for IC601. IN-1 is the left audio channel and IN-2 is the right audio channel. The outputs from Q601 are pin 2 (left audio) and pin 12 (right audio). When probing the output, ake sure the ground side is connected to either pin 4 or 10, depending on the output being tested. The audio output does not reference a common ground.

     Another technique for testing the audio signal is to scope the variable audio output located on the rear of the unit. A signal here will indicate the audio signal is present from the pre-amp driver (IC663).

MUTE

     The next following diagrams will cover mute controls. All mute signals are generated from the main micro and this TV has several selections of mute control. One mute control is through the TV’s menu as main speaker “on” or “off”. Another control is the mute key located on the remote control. This feature has three selections: ½ mute, mute and off. The ½ mute is an I2C controlled feature to the IMA board H002, not part of the any mute circuits. Basically stating, when the ½ mute is selected, the IMA circuit receives this command from the main micro and the IMA circuit reduces the audio level by ½ depending on the initial audio level.

     Another audio mute is done during channel change and no signal conditions; this is called the Mute–A line. See Figure 15. A signal from the main micro on the Mute-A line will apply a voltage to the base of transistors Q681 and Q682. With these NPN transistors “on”, the audio output lines from the preamp IC663 is pulled to a ground potential and no audio signal is input to IC601 amplifier.  Under normal conditions, the base of transistors Q681 and Q682 will be 0 volts.

     Speaker Mute is a feature located in the user menu, allowing the speakers to be turned “on” or “off”. The control line is referred to as SP_MUTE in the schematics. See Figure 16 for circuit details. Checking this circuit can be as easy as checking the voltage at pin 9 of IC601, as shown in Figure 16 with the “5V=Mute On”.

     Step back for a moment and follow the SP_MUTE signal sent from the micro. The SP_MUTE voltage is applied to the base of Q614, allowing it to conduct. This removes the 5V line from the base of Q613 and turns “off” this PNP transistor. This allows the 5V potential to be applied the pin 9 of the audio amplifier. Pin 9 is IC601’s internal mute circuit. In a normal condition, Q614 is “off” and Q613 is “on”.