Bu1 Board Protection; Onboard Regulator Protect; Thermal Protect; Panel Protect - Sony KDL-26S3000 Training Manual

BU1 Board Protection

The BU1 board has several protect monitoring circuits for its own DC
voltage regulators. Monitoring of temperature, speaker protection and an
inverter failure are also included. A block diagram of these protect circuits
is illustrated in Figure 1-11

Onboard Regulator Protect

The regulated 2.5 volts for Trident IC4500 is monitored. If this voltage fails
A DC_ALERT 1 high will occur on pin 163 of the Main Micro IC3001. The
unit will shut down and the power LED will flash in groups of 3.
Similarly, if the D1.0V or D1.8V sources (generated on the BU1 board)
fails a high will be placed on pin 153 and the unit will shut down generating
groups of 4 blinks.
The regulated 12V is the only outside voltage monitored. It sources from
the power supply and will keep a specified high on pin 82 of the Main
Micro. If the voltage fails or falls below this specified limit, the unit will shut
down and blink the power LED in groups of 2. Note that this 12V line is
also the source for the Panel 12V which is switched by the main micro.
This voltage is also monitored by Main Micro at pin 154 (DC_ALERT_3).
If the 12V from the power supply is OK but failed on the Panel_12V line,
the unit will shut down and blink the power LED in groups of 5.

Thermal Protect

IC3007 is a digital thermometer that can be programmed to send data to the
Main Micro when a specified temperature level is reached. The purpose of
the thermal sensing is to monitor the unit for excessive temperature within
the unit during operation. If the temperature rises above the specified
threshold the unit will shut down and display groups of 6 blinks from the
power LED.
Note: IC3007 is constantly polled by the Main Micro. If the IC were to
fail or the data line on the I²C to open the unit would shut down within
approximately 10 seconds. It is important to beware of this. If a unit shuts
down immediately, it can be safely assumed that the television is not
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Chapter 1 - Features and Circuit Descriptions
running hot. Shutdowns after extended periods would warrant checking
the location of the unit for proper ventilation.

Panel Protect

If the high voltage generated by the inverter were to fail, or if abnormal
current conditions are detected on the balancer circuits, a high would be
applied on pin 81 of the Main Micro. The unit will shut down and blink the
power LED in groups of 6.

Audio Protect

If any DC is detected on the left or right speaker channels the unit will shut
down and blink the power LED in groups of 8. This symptom is usually
caused by a failed audio amp and would require the replacement of the
BU1 board.
Balancer Protect
Along with a Panel Protect line, a Balancer Error line is connected to pin
81 of the Main Micro. Working in conjunction with panel protection, both
lines connect to a voltage divider. The voltage at pin 81 is normally 3.3
volts. If an inverter error is detected, the line (normally low) will go high
and the inverter transistor will pull the voltage down to zero. A balancer
error would complete the divider network and pull the voltage down to
about one-half (1.8 volts). This is how IC3001 is able to tell which type of
error has occured.
NOTE: The 26" and 32" models do not have a balancer error line from the
inverter board. Only the 40" and 46" models have this feature.
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