- One feature that has been removed from the MIX-5 chassis design is the red standby LED. In previous models, the power/standby LED remained lit in red. It turned green when the power was turned on. The power LED in the MIX-5 chassis will turn red, but only for diagnostics indications. A lit standby LED was a good troubleshooting tool since it clearly indicated a functioning standby power supply (one of the first items to check when a unit will not turn on). Without the standby LED to provide a clear indication of standby power, other methods must be used to test this stage. The first test is to listen carefully for the sound of two relay clicks. The main relay (RY6001) should engage followed by the in-rush current relay (RY6002) engaging approximately 1.5 seconds later. It is possible to hear only one relay click. This indicates the in-rush current relay may not have engaged and the unit will go into protect shutdown with and 6-blink diagnostics indication.
- The B 12V line is monitored for excessively low or high conditions and the power LED will blink 6 or 8 times respectively if there is a problem. The Q10.5V is also monitored for over-voltage and will cause the diagnostics to blink the LED 10 times.
- If the entire switching regulator fails to start, the diagnostics circuit will blink the power LED 6 times. This can be misleading since it could cause the technician to immediately suspect the GT power supply board as the culprit.
- A Note on 6-Blink Shutdown Indications: Any time the power supply does not start, the Main Micro (IC8002) on the AGU board will detect the loss of B12V. Since the Main Micro (IC8001) is always running on standby voltage, it assumes there has been a failure of the B12V line (in fact, there technically is). If the main relay (RY6001) were to fail, the main switching regulator would not turn on (even though IC8001 has commanded it to). This causes a misleading diagnostics indication. Any excessive loading of the secondary voltages can cause the switching regulator to turn off since there is over-current monitoring within the circuit. If the thermal fuse (located within the lamp assembly) were to open, standby 5V would no longer be applied to the main relay (RY6001). The main switching supply would never turn on and an erroneous 6-blink shutdown would occur.
- If a 6-blink shutdown occurs, always listen for the sound of relay clicking. If none is heard, the main relay could be defective (unlikely), the standby supply has failed, or the thermal fuse is open. Reading the voltage at the thermal fuse easily checks the presence of standby 5V. If no voltage appears on either side, the standby supply is not working. If 5VDC appears on one side and not the other, the fuse is open. If voltage appears on both sides, the main relay is defective or is not being told to turn on.
- The self-diagnostics feature incorporated within the MIX-5 chassis is a valuable tool in determining what board might be the likely cause of a failure. In most cases it leads the technician towards the potential source of the failure. In some cases, the diagnostics indication is rather vague. A perfect example of this would be a 4-blink event indicating a cooling fan failure. This could be caused by lack of B+ drive to the fans, lack of fan control, or the failure of a singe fan.
- In a situation such as this, the technician must arrive at the service location with the AGU board, 3 different fans and the optical block. Fan 1, located inside the optical block is not available for replacement. The other 3 fans, Fan 2 inside the lamp driver/housing assembly, Fan 3 (main intake), and Fan 4 inside the B Block assembly can be replaced as individual items.
- CN8002 on the AGU board supplies power to all 4 fans. This is observed in Figure 2-2 in this Chapter. The fan rotation-detect line for each individual fan is also located at this connector. Each fan receives approximately 5VDC of drive voltage under nominal conditions. The rotation-detect lines are normally low (less than 1VDC). In past chassis designs, over-temperature conditions and fan rotation errors were included in the same diagnostics error indication. If a thermal IC failed, the fans would not be turned on. This unit must turn the fans on to detect rotation. This allows a moment for each rotation-detect to be tested before the unit goes into protect mode. It also allows the ability to check if the fans are receiving drive voltage.
- Protect events occurring with a 6-blink diagnostics indication can be misleading.
- Don’t become dependent on the self-diagnostics feature of this television. Use it as an additional tool in isolating the cause of a problem. Traditional analysis of symptoms based on what you see or hear (or don’t see or hear) should always be utilized in conjunction with this feature.
AUDIO
All switching and processing of audio signals are performed
on the AGU board. Amplification is done on the K board. In a situation where no
audio is present from all inputs, the AGU or K board could be the cause. A
simple way to isolate this issue is to use the television’s audio output jacks
and connect them to an external amplifier. If audio is present, the K board is
not the cause. The problem resides on the AGU board.
VIDEO
- Since virtually all video processing is performed on the B board, failures are likely to be traced to this point. This is especially true if distortion is evident in the picture. Since most of the video processing is done at the digital level, the distortions will usually appear as digital blocking or loss of picture detail. Failures on the QM board can also create the same distortions but it is part of the B Bock and replaced together with the B Board.
- The AGU board is responsible for routing all video sources other than the ATSC digital information. Failures here would cause a loss of one or more of the video inputs (including the PC input) but would not affect signals from the ATSC tuner.
- A powerful tool for troubleshooting a loss of video (or distortion) is the internal service data graphics and various test graphics generated on the QM and C boards. When the service mode is entered (unit turned off and “DISPLAY”, “5”, “VOL+”, “POWER” pressed in sequence on the remote commander) the default graphics will be the general service mode. Large green letters will appear on the screen. This is an indication that the Main Micro on the AGU board is communicating graphic data ATI Micro on the QM board (where all digital video decoding is performed for ATSC signals). It also eliminates the B and C boards as the possible cause of the loss of or distortion in the video signal since the graphics are being processed.
QM GRAPHICS
- In situations where video failures occur only when ATSC channels are selected, the graphics generated by the QM board are helpful. By pressing “JUMP” on the remote commander, the test data graphics will change from green to blue. If these graphics appear, the circuits on the B and C boards are functioning. The B block should be replaced. Other test pattern graphics are available to assist in alignment and overall examination of how well the unit is scaling the various formats specified by the ATSC
- In the QM service group, press the “1” key on the remote to select Item 1 labeled “PATN”. Using the “3” key to change the data value will scroll you through various test patterns. 4 groups of 20 patterns are available for each resolution. They are as follows:
21-40: 480i
41-60: 480p
61-80: 720p
- Additional graphics are available by selecting item 2 (GPTN). All of these graphics are 1808i and generated by the same circuit that displays the customer user menu so they will not fill the screen entirely.
BE GRAPHICS
- The BE Micro located on the C board directly generates graphics to the scaling IC just before the LCD panel drivers. Press the “JUMP” button on the remote until smaller green letters and numbers appear. The fact that these can be seen is a good indication that the C board is functioning properly and the optical block will not need replacement.
- Additional test graphics are located in this circuit. The most useful is the ability to generate various “flat field” patterns in white, black, and each primary and secondary color. This is extremely useful for troubleshooting suspected problems with a particular LCD panel.
- These patterns are accessed by going to group 32 while in the BE mode.
- Use the “5” key on the remote to scroll to this group number. It is called “D8909TPN”. Using the “1” key, scroll to Item 1 labeled “PNRGB”. By pressing the “3” and “6” key on the remote various flat field colors are displayed as mentioned above.
- NOTE: Always return screen to white (data 0007) when finished. If this is not done, additional test graphics located in the BE micro will be displayed in that color. None will be displayed if left in black field (data 0000) mode.
- Do not turn the unit off while in the BE service mode. When you turn the unit off and back on, the BE graphics will still be present and you will not be able to control them because the remote commander is back in the conventional mode. If you accidentally do this, unplug the unit to perform a hard reset of the microprocessors and the unit will operate correctly.
If the lamp fails to light, there will be video
(for obvious reasons). By reading voltages with a multi-meter, it can be
determined if the lamp is not lighting because of a failed lamp, lamp driver,
or power supply issue.
