PHILIPS TV FM23 - PLASMA DISPLAY - POWER SUPPLY VOLTAGES – HARDWARE ALIGNMENTS – SMPS BOARD WORKING

TV FM23 - Philips Plasma Display - POWER SUPPLY VOLTAGES – Hardware Alignments – SMPS board working

Vs and Va alignment
VS Alignment
Measure VS on pin 10 of connector 0323 (diagram P7).
Use pot meter R3026 (see diagram P6) to align this voltage to the value mentioned on the sticker (mind you: alignment accuracy = ± 0.5 %)
VA Alignment
Measure VA on pin 1 of connector 0323 (diagram P7). Use pot meter R3127 (see diagram P7) to align this voltage to the value mentioned on the sticker (mind you: alignment accuracy = ± 0.5 %).

Hardware Alignments
After a Power Supply, replacement, you must align both VS and VA voltages. The exact values differ from panel to panel, therefore a sticker with the correct values is placed on the PDP.
1. Replace the Power Supply panel.
2. Set the monitor in Service Default Mode.
3. Allow the set to warm up for 20 minutes.  Use a calibrated volt meter (accuracy = ± 1%) for the following alignments.
For the correct alignment values, check the sticker in the upper left corner of the PDP (located just behind the suspension bracket, see photo below)

Software Alignments
Enter the Service Alignment Mode (see chapter 5). The SAM menu will now appear on the screen.
Select one of the following alignment menus via the upper horizontal bar:
1. General (Gen.)
2. Display (Disp.)
3. Scaler (Scal.)
4. Video 1 (Vid.1)
5. Video 2 (Vid.2)
6. Options (Opt.)
Note: the last three items are not available in the Basic configuration.

Select this item, and press OK, to store the made alignments.  Note: There are several methods to exit the SAM, each with its own characteristics:
• Switch the set 'off' (with the Mains switch or by pulling the Mains cord); new alignment settings are always stored, even when item 'store' was not activated.
• Switch the set to 'standby' by pressing the power button on the remote control transmitter; new alignment settings are always stored, even when item 'store' was not activated.
• Use a standard RC-transmitter and key in the code 0 0; new alignment settings are not stored (except when item 'store' was activated).

SMPS BOARD FUNCTIONS

The PSU consists of a pre-conditioner part and a DC/DC converter part. This converter supplies power to the PDP high voltages, the auxiliary voltages, and the audio amplifier. There is a separate standby power supply, which supplies the Main Processor, PDP microcontroller, interrupt generator and some other circuits. 

The mains inlet module will host the inlet and filtering.  There is a functional 'Mains on/off' switch on the LED panel.  This switch is on the secondary side, controlling the relays on the primary side.

POWER SUPPLY VOLTAGES

SMPS working principles

The Power Supply Unit (PSU) is designed to provide regulated output voltages for the plasma display panel (PDP) and the built-in electronic panels (such as e.g. the SCAVIO and Audio Amplifier panels).
It will house the Pre-conditioner, DC/DC converters and the Standby circuitry. In addition, this panel will house the protection and the (optional) fan drive circuitry.  The Mains inlet is mounted alongside the SCAVIO panel. It consists of the necessary high and low frequency mains filters.
The mains AC voltage is applied to the input filter and then fed to the standby supply. This supply is always operational and delivers the +9VSTBY voltage.  The task of the main supply is to deliver the supply voltages for the several electrical circuits in the monitor.  It is switched via two single-pole relays, which are powered from the +9VSTBY voltage and controlled via the SUPPLY_ON signal.
The reason to choose for a separate standby supply instead of a single flyback supply is the requirement to have a low standby power consumption.

The PSU consists of the following parts (which are described separately):
• Mains inlet and filter,
• Standby supply,
• Fan control (optional),
• Pre-conditioner,
• LLC supply,
• Aux. supply,
• Protections.

Mains Inlet and Filter

The mains filter provides common-mode and differential-mode filtering, to fulfil legal and self-imposed limits. Additional provisions are mains spikes and lightning protection.

Operation

The mains voltage is provided via mains inlet 0308, after which it is fused by a T6.3A fuse (item 1400).

The next part, the mains filter, is optional. It consists of an LC common mode filter section. This filter consists of two capacitors (items 2402 and 2403) from both phase and neutral to ground (to reduce the leakage current) and an inductor (5401). Interferences on one of the phases are shorted to ground via these capacitors.  Inductor 5401 also provides a differential-mode filtering with capacitor 2400. Resistor 3401 discharges this capacitor after the mains is disconnected.  A second common mode filter is made around coil 5402 and capacitor 2401.

Resistor 3400 is a high energy VDR. The advantage of this VDR is that it can handle 400 V AC without risk of fire. At high voltage peaks (e.g. lightning surge) on one of the phases, the resistance of VDR 3400 will be very low, causing fuse 1400 to interrupt.  At a lightning surge on both phases with respect to chassis ground, mains filter 5401 will form a high resistance, through which the voltage will rise very sharply.  To prevent flashovers, a spark-gap/ resistor combination (items 1402 and 3404) is implemented.  The high-ohmic resistors 3402 and 3403 are connected between neutral and chassis ground. They are required by safety regulations.

Standby Supply

The standby supply is a separate power supply, meant to reduce power consumption of the Flat TV monitor in standby mode. The standby supply operates on the AC voltage from the input filter part, and has to deliver a stable 9 V voltage.

It has three mains isolated outputs, and one 'hot' output:
• +9VSTBY (called +9VSTBY_SW after the 'on/off' switch 1101), to power the 'on'/'off' relays in the pre-conditioner.
• +5VSTBY_SW (derived from the +9VSTBY via voltage regulator 7540)
• +3V3STBY_SW, to supply the µP of the PDP.
• 25V_HOT, to supply the LLC controller.

The standby supply is also connected to the pre-conditioner output (400V_HOT), in order to deliver a voltage as long as possible, after switch 'off' and at mains dips.

Operation

The standby supply is always operational when the AC input voltage is present, so even when the POWER switch is in the 'off' position. After a small rectifier (D6512/6513) and buffer capacitor (C2503), the DC voltage is applied to an SMPS (switched mode power supply).  The SMPS itself is build around IC7500, a 'TINYSwitch TNY256'. This IC contains a control circuitry and a power MOSFET. It uses a simple 'on/off' control loop to regulate the output voltage. The generated +9VSTBY voltage, at the secondary side, is rectified by D6504 and smoothed by C2508.  The supply for the TNY256 on pin 6 comes via resistor R3506 and L5500.  By using secondary sensing, a very accurate standby voltage and high efficiency is achieved. The sensing circuit uses a TL431 as reference voltage/error amplifier. Optocoupler 7501 is used for the mains isolation.  When the output voltage rises, the reference voltage on the TL431 will exceed 2.5 V and the current through this device and the optocoupler LED will increase. By this, the optocoupler transistor will conduct more. When this current (at pin 4 of IC7500) exceeds 50 µA, the MOSFET is switched 'off', and the output voltage will drop. When this current drops below 40 µA, the MOSFET is switched 'on' again.  During the time that the MOSFET is 'on', the IC has no supply voltage. To overcome this period, the energy stored in the bypass capacitor C2513 is used. This capacitor is charged during the time the MOSFET is 'on'.  As the TNY256 is sensitive for transients (mains spikes), a 'peak clamp' circuit (300 V zenerdiodes 6501 and 6502) is used to limit the voltage to a safe level.