SONY KV-32FV16 - KV36FS16 - SELF DIAGNOSIS [AA2U CHASSIS] - POWER SUPPLY
BLOCK - WORKING PRINCPLES & TROUBLESHOOTING - HOW TO CHECK A MOSFET
The AA2U chassis uses combinations of blinking Standby/Timer LED and Stereo LED statuses to indicate failures. As in other chassis, the Standby/Timer LED will blink during Vertical and AKB failures. These are indicated by the Standby/Timer LED flashing in sequences of four for a verti-cal failure indication, and flashing in sequences of five for AKB failure indication. The set does not shut down during these failures. This allows for some troubleshooting when a failure occurs. This information is also logged in IC002 NVM.
When the set is first turned ON, a Power Supply failure
would be indicated by the Standby Timer LED flashing three times, then turning
off, and then the Stereo LED coming ON. These problems are also accompanied by
the Power Relay turning OFF due to the latch circuit being activated.
The Standby/Timer LED flashing three times at Turn ON then
turning OFF and the Stereo LED remaining OFF indicate loss of I²C data. The set
will have no other functions if this occurs.
AKB FAILURE
The purpose of the AKB circuit is too ensure that the white
balance that was set up at the factory is maintained. Sending a one-H pulse for
each color during the vertical blanking interval from the YCJ does this. The
current drawn by the tube during the time these pulses are generated is fed
back to the YCJ and it adjusts the drive levels for each color to maintain the
correct white balance. If the correct white balance cannot be obtained, the YCJ
indicates this to the Tuning Micon via the I²C bus. The Tuning Micon would then
pulse the Standby Timer LED so that it flashes in sequences of five. In this
set, unlike other Sony sets, the video will not be blanked at this point. After 11 seconds the picture will
appear and be discolored because one or more of the tubes cathodes are not
operating correctly.
VERTICAL OR HORIZONTAL FAILURE
Vertical failure is detected by sending the pump-up pulses
from IC561/6 to a sample and hold circuit. This circuit outputs a HIGH to
IC355/15 VM Out/V Protect. This pin is used only for vertical protection in
this set and not for Velocity Modulation. If a fault occurs that causes the
pulses at IC561/6 to disappear, the sample and hold circuit would pull IC355/15
down to a LOW. This would cause IC355 YCJ to blank the video outputs and alert
IC001 Tuning Micon that a vertical failure has occurred. The Tuning Micon will
pulse the Standby Timer LED so that it flashes in sequences of four. If the vertical failure were intermittent,
the picture would return when the circuit started working again. However, the
Standby/Timer LED would continue the flash as it did when the vertical failure
occurred. If a customer complains about an intermittent picture, ask how many
times the Standby/Timer LED is flashing.
If horizontal failure occurs then no HP pulse will be sent
to IC355/18 HP/PRM. When this line goes LOW, the HD signal from IC355/19 is
disabled. This causes the horizontal circuit to shut down. Since rectified
signals from the FBT are used to create the +12 and –15 volts that sup-plies
the vertical output, loss of horizontal will cause vertical failure to be
indicated.
Once a horizontal shutdown occurs, the set cannot return to
normal operation until it is turned OFF and then back ON. This is because once
the HD is removed because of a LOW on the protect line, it will not be
re-started until power is cycled to the YCJ.
Problems with the horizontal or vertical
circuits can cause a vertical failure to be indicated by the Self-Diagnostics.
Two indicators that point to the horizontal circuit are lack of High Voltage
and lack of heater filaments glowing. It is often difficult to determine by
listening or looking whether there is High Voltage present or if the heaters
are glowing. If you are unable to determine if these things are present, check
the following to determine which circuit is at fault
CHECKS
- Check for +12 and –15 volts at R536 and R537. If one or both of these voltages are missing, check to see if the FBT signal is present on the other side of each resistor. If the signal is not present at these resistors, it indicates a horizontal problem.
- If the signal is not present at these resistors, check for the HP signal at IC355/18. If this signal is LOW, it indicates that something is wrong with the horizontal section and the horizontal drive at IC355/19 will be disabled. Troubleshoot the horizontal circuit.
- Horizontal drive should be present when the set is initially turned ON. You can troubleshoot this section by continuously turning the set ON and OFF and tracing the horizontal drive signal to the horizontal out-put. A shorted horizontal output would not be an issue under this circumstance since that kind of failure would cause power supply shutdown.
- If +12 and –15 volts are present, check for Vertical Drive at IC355/13 and 14. If these signals are present, troubleshoot the vertical output circuit. These signals should be present during vertical failure. If they are not, replace the YCJ.
I²C Problems
Q016 and related circuitry form a voltage regulator, which
is used to sup-ply power to the I²C data line through pull-up resistor R1117.
The purpose of this circuit is to reduce the level of the I²C data if the
9-volt line is LOW. If this occurs, the data will not be recognizable to the
ICs on the bus. When this data is LOW or missing, the set will turn ON normally
with three clicks but there will be no sound, video, LEDs and vertical
deflection. Horizontal and High Voltage will be perating normally. Glowing
heater filaments are an indication of normal horizontal operation.
POWER SUPPLY BLOCK
The power supply in the AA2U chassis is located on the G
board. It is nearly identical to the power supply in the AA2W chassis. AC from
the outlet is applied to a series of line filters and protection devices and is
eventually applied to the standby supply, AC rectifier and degauss circuits.
The Standby supply is a switching supply whose output is applied to a 5-volt
regulator. The output from the regulator exits the G board at CN641/10. It is
applied to various components in the set that need to be powered when the set
is OFF. These include the Micon, remote sensor and S Link circuitry if
applicable.
When the set is turned ON using the power button, remote
control or S Link, 5 volts is applied to CN641/11. This 5 volts is used to turn
RY600 Power Relay ON. When the relay closes, a click is heard. Closing the relay
allows the AC voltage to be rectified and applied to the converter circuit. The
converter begins operation when this voltage is applied. The power ON line is
also applied to the soft start circuit. The soft start circuit holds the B+
voltage low while the power supply capacitors charge by controlling the voltage
present across the control winding. The control winding determines the
switching frequency of the converter. After soft start operation is complete,
the regulation circuit takes over operation of the control winding. The
regulation circuit produces an error voltage by monitoring the +135 volt line. This allows the converter’s
output to be coupled through T605 to the secondary supplies. These secondary
sup-plies power the rest of the set.
The power supply in the AA2U chassis is located on the G
board. It is nearly identical to the power supply in the AA2W chassis. AC from
the outlet is applied to a series of line filters and protection devices and is
eventually applied to the standby supply, AC rectifier and degauss circuits.
The Standby supply is a switching supply whose output is applied to a 5-volt
regulator. The output from the regulator exits the G board at CN641/10. It is
applied to various components in the set that need to be powered when the set
is OFF. These include the Micon, remote sensor and S Link circuitry if
applicable.
When the set is turned ON using the power button, remote
control or S Link, 5 volts is applied to CN641/11. This 5 volts is used to turn
RY600 Power Relay ON. When the relay closes, a click is heard. Closing the relay
allows the AC voltage to be rectified and applied to the converter circuit. The
converter begins operation when this voltage is applied. The power ON line is
also applied to the soft start circuit. The soft start circuit holds the B+
voltage low while the power supply capacitors charge by controlling the voltage
present across the control winding. The control winding determines the
switching frequency of the converter. After soft start operation is complete,
the regulation circuit takes over operation of the control winding. The
regulation circuit produces an error voltage by monitoring the +135 volt line. This allows the converter’s
output to be coupled through T605 to the secondary supplies. These secondary
sup-plies power the rest of the set.
Shortly after the click of the power relay at turn ON,
another click is heard. This click is
RY601 Degauss Relay closing. This may be accompanied by a hum sound that
indicates the operation of the degaussing coils. There is a third click that
occurs about 8-10 seconds after the unit is turned ON. During operation of the set the +135 volt
line is monitored for DC protection. This protection circuit is used in
conjunction with the latch to switch the Power ON line LOW if a failure should
occur. This will turn RY600 Power Relay OFF and turn the power supply OFF. In
addition, a fold back circuit can also shut down the power supply. The fold
back circuit com-pares the secondary +12 volt output to a voltage on the
primary side. If there is a problem with either one of these circuits, the set
will be forced into soft start mode. This will cause the set to shut
down.
TROUBLESHOOTING
OVER CURRENT PROTECTION [OCP]
Use this drawing to quickly check voltages on the G board
connectors. These connectors can be
accessed by pulling the three boards at the bottom of the chassis towards the
rear about 3 or 4 inches.
The standby power supply is a switching power supply used to
create Standby 5V. The Standby 5V line is used to power the Tuning Micon, EEPROM
and any other circuits, which require power when the set is OFF.
Monitoring the voltage across R637 is used for over current
protection. This voltage is
representative of the amount of current flowing through Q621 Converter since it
is in series with the transistor. If this voltage should rise to .6 volts, it
will cause Q622 to turn ON. If Q622 were to turn ON, it would shunt Q621/G
voltage to ground. This would cause Q621 Converter to stop conducting. This is
a non-latching protect circuit.
OVER VOLTAGE PROTECTION [OVP]
Over voltage protection is performed by rectifying the
voltage at T621/6 with D627. This voltage is filtered by C636 and applied to
D626 through R638. If this voltage should rise above 6.2 volts, D626 begins to
conduct. When its conduction allows
Q622 Protect to turn ON, over voltage protection is employed. Q622 Protect
turns ON and grounds Q621/G, which stops the converter from switching. D699 is also used for OVP. The signal from
T621/4 is rectified by D698.
This creates a negative voltage across C699. If this
negative voltage becomes great enough, D699 conducts and the Q621/G voltage is
brought lower. Both of these protect circuits are non-latching.
SECONDARY OUTPUT
The power coupled through T621 SRT places a voltage on
T621/9, which when rectified and filtered by D628 and C637 is 7.2 volts. This
voltage is constant due to the regulation circuit on the primary side of T621
SRT. This 7.2 volts is applied to
Q646/E for backup during the start of regulation by the regular power supply.
It is also applied to IC622 5-Volt Regulator, which
regulates its output to 5 volts. This 5 volts is sent to CN641/10 which
connects to the A board and powers the Tuning Micon and other circuits. It is
also applied to RY600 Power Relay.
CHECKING Q623 [MOSFET]
Testing a MOSFET device is easy. The leads show infinite
resistance to every other lead except for drain to source in one direction
because of the presence of a protection diode.
To prove the device is functional:
- Connect the negative lead of the ohmmeter to the SOURCE lead.
- Touch the ohmmeter positive lead to the gate to pre-charge it.
- Connect the ohmmeter positive lead to the DRAIN. If the device is good, you will get a resistance reading of about 400-1k ohms. Some DVMs do not produce enough DC voltage in the ohms mode. The diode check mode can be used with these models. When using the diode mode, a low voltage drop is shown after pre-charging the gate.
