Toshiba PROJECTION Schematic

TOSHIBA Service Training

PROJECTION

TELEVISIONS

Main Power Supply

NTDMOD02

& Complete

Shutdown Guide

TP43H60 TP43H95 TP50H15 TP50H50 TP50H60 TP50H64 TP50H95 TP55H60

TP55H64 TP55H95 TP61H60

TZ43V61 TZ50V51 TZ50V61 TZ55V61 TZ61V61

Contents

Main Power Supply...............3

Overall Block Diagram .................................................................................... 4

Operation........................................................................................................... 5

Surge Protection Relay ................................................................................... 6

Start-up and Over Voltage Protect ................................................................. 7

Logic and Drivers............................................................................................. 8

Oscillator ........................................................................................................... 8

Oscillator Control ............................................................................................. 9

Latch .................................................................................................................. 9

Thermal Shock Detection Block .................................................................... 9

Over Current Protection................................................................................. 1 0

Soft Start ........................................................................................................... 1 0

Resonance Correction ................................................................................... 10

Additional Information on Q801 .................................................................... 11

Block Diagram of Q801 (STR-Z4117) ............................................................ 11

Pin Descriptions .............................................................................................. 11

Waveforms ....................................................................................................... 12

Troubleshooting Flowchart ........................................................................... 13

Shutdown Guide.................15

Summary of Shutdown Circuits .................................................................... 1 6

Peak-Response Meter .................................................................................... 17

No Peak-Response Meter .............................................................................. 18

Monitoring Circuits ......................................................................................... 18

X-Ray Protect ................................................................................................... 19

+125V Over Current Protect .......................................................................... 20

+36V Over Current Protect ............................................................................ 2 1

+18V and – 18V Over Current Protect .......................................................... 22

+35V Over Current Protect ............................................................................ 2 3

+9V Under Voltage Protect ............................................................................. 24

+35V Under Voltage Protect ...........................................................................24

+200V Under Voltage Protect ........................................................................ 24

Troubleshooting Flowchart ........................................................................... 25

Main Power Supply

Overall Block Diagram

Figure 1 is the overall block diagram of the main switching power supply and the standby power supply . The standby supply is always acti ve when the television is plugged into an AC line source. This supply delivers a 5V VDD and a Reset 5V to the microprocessor to keep the microprocessor functioning at all times, even when the television is not operating. Transformer T840 isolates the standby supply from the live ground, and D840 is a fullwave bridge rectifier that supplies 12Vdc to voltage regulator Q840 and relay SR81 (connection not shown). When the microprocessor receives an ON command from the remote control or power key, on the front of the television, it sends 5V to relay drivers QB30 and Q843 to close relay SR81.

Stand-By Supply

Rectifier &

Isolation Trans.

D840 T840

AC Line Input

QB30 Q843

SR81 Relay

Stand-by

Regulator

Q840

5V=Relay On 0V=Relay Off

Relay Drivers

Rectifier

D801

+5-1

From Shutdown

Main Switching IC

165V

Microprocessor

VDD

Reset

QA01

Q801

Feedback

C870

T862

Photo

Coupler

Q862

When the relay closes, the A C line input is applied directly to the main power supply . The supply starts to operate and turns ON the television. D801 is the full-wave bridge rectifier for the main power supply. It rectifies the 120V AC line input to 165Vdc and applies it to the main switching IC, Q801. The primary side of the power supply is not isolated and, therefore, is at live ground. Detailed explanations of the main power supply are covered in the remainder of this section.

Troubleshooting Tip: If SR81 never closes, check the standby power sup-

ply . Both the 5V VDD and the Reset 5V are mandatory for the microprocessor to operate.

Main Power Supply

To Q752 Conv. Output

To Q752 & Q751 Conv. Outputs

To Digital Conv. PC, Q764 & Q767

To Q752 Conv. Output

To Q752 & Q751 Conv. Outputs

To Digital Conv. PC, To Q601 Audio Out

To Q501 Horizontal Start-up

To Shutdown & Surge protect: Q846,SR82,Q757, & Q758

+9-2 To Numerous Circuits

+5-2 To Numerous Circuits +9-1 To Numerous Circuits

+5-3 To PIP Module & QBB3

To Horizontal Output To Tuner(s)

Reg.= Regulator Conv.= Convergence

11 9

Rectifiers

D856 D855

D851 D854

D886 D889

D891 D894

D882 D884

Error

Amp.

+36

+18

-18

+38

+12

+125

Z801

Q760

Q754

Q755

Q756

Q430

Q832

Q830

Q831

D101

30V

Reg.

-9V

Reg.

5V&9V

Reg.

32V

Reg.

Figure 1.

Power Supply Block Diagram

Operation

The main power supply is a current resonant switching power supply. Figure 2 is a basic block diagram for this supply . The primary winding of T862 and capacitor C870 create an LC series resonant circuit. An oscillator (OSC), dri ve circuit, and two MOSFETs are located internally to Q801 (STRZ4117). The OSC determines the power supply’ s switching frequency . The dri ve circuit alternately switches the MOSFETs ON and OFF. The two power MOSFETs, in a push-pull configuration, alternate the current flow through the LC circuit during normal operation. The alternating current continually builds and collapses an electromagnetic field around T862’s primary windings. The collapsing of the electromagnetic field induces current into the secondary windings of T862. A fullwave bridge rectif ier con verts the induced current into 125Vdc. To regulate the 125Vdc, an error amplifier moni-

rent, the oscillator frequency decreases and operates closer to the LC resonant frequency . The closer the switching frequency is to resonance, the higher the current flow through the primary windings of T862 and the larger the electromagnetic field. The larger the electromagnetic field is when it collapses, the higher the induced current is in the secondary winding. When the load decreases and requires less current, the switching frequency increases and moves aw ay from resonance. As a result, less current is induced in the secondary windings.

Load

Current

Increased

Load

O S C

i v e

Q801

T862

C870

Photo

Coupler

Q862

125V

Error

Amp

Z801

Figure 2

Operational Block Diagram

tors the voltage and supplies a negative feedback to the oscillator through photo-coupler Q862. Q862 isolates the primary side of the power supply from the secondary side. Refer to Figure 3. The power supply’s switching frequency operates above the LC resonant frequency. When the load on the secondary side of the power supply increases and requires more cur-

Decreased

Load

Resonant Freq.

Normal Operating Frequency is 70-80kHz

Operating Freq.

Switching

Freq.

Figure 3

Load Current Characteristics

Surge Protection Relay

Figure 4 shows the surge protection oper ation. T o prolong the life of the power supply , a sur ge cir cuit reduces current through the main power supply at startup. When the television is OFF, relays SR81 and SR82 are open. At turn-on, SR81 closes and the switching power supply begins to operate. During this time, the power supply draws a large amount of current. T o reduce the current, the ground path for bridge rectifier D801 is through resistor R810. Once the power supply becomes fully operational and produces output voltages, one of these voltages is applied to the base of transistor Q846. This voltage turns Q846 ON and allows current to flow through the coil of SR82. SR82’ s switch closes and creates a direct ground path for D801 by bypassing R810. SR82 remains closed during normal operation.

Troubleshooting Tip: R810 is a fusible resistor . If SR82 does not close

after the power supply is fully operational, R810 eventually opens and prevents the power supply from operating. Whenever troubleshooting the power supply , check R810 first. If R810 is open, replace it, using T oshiba part number 24007061, and look for cold solder joints around Q846 and R846.

Relay SR81

R809

R810

Main Power Supply

Q801

D801

T862

SR82

Figure 4

Surge Protect

and

125V

12V

R846

Q846

Start-up and Over Voltage Protect

The positive cycle of the AC line input supplies a 16V start-up pulse to pin 8 of Q801 via resistor R861. Figure 5 is the block diagram for this circuit. After start-up, a dri v e circuit consisting of a secondary winding of T862, diode D864, and capacitor C868 supply 16-20Vdc to pin 8 of Q801 to maintain its operation. The voltage developed by the drive circuit fluctuates with the switching frequency of the power supply. Therefore, the voltage on pin 8 is also applied to an over voltage protect (OVP) block internal to Q801. If the v oltage on pin 8 increases to 25V, the OVP triggers the latch and switching stops. Refer to the Latch section for further information. D876 is a 27V zener diode that protects Q801 by preventing excess voltage increases on pin 8.

From D801

R861

16-20 Vdc

OVP

Start

D876

Vcc

Q801

D864

Figure 5

Start-up and Over Current Protect

R871

T862

C868

Logic and Drivers

OSC

R867

Q801

Oscillator

As shown in Figure 6, the logic block controls the MOSFETs’ switching frequency. The outputs of the logic block feed two drivers that are powered by the start block. After the start-up voltage is applied to pin 8, the start block supplies a drive Vcc (DRI Vcc) of approximately 8V to pin 9. Delaying the driver supplies at start-up prevents damaging the MOSFETs. The 8V on pin 9 powers driver B internally . T o power dri ver A, resistor R862 and diode D862 add the voltage from pin 9 to the voltage on pin 15. D875, C863, D873 and C873 are voltage regulators and filters for these supplies.

D873 C873

R862 D862

D875 C863

V 1

B+

130V

Out 14

COM. 12

To T862

Start

Vcc

DRI Vcc

915

Logic

Q801

Refer to Figure 7. Q801’s internal Oscillator develops the power supply’ s switching frequenc y by generating a ramp waveform internally. During normal operation, both MOSFETs are OFF for a short time when they are alternately switching. This OFF time is called dead time and determined by the value of resistor R867 on the dead time (DT) terminal pin 7.

Figure 7

Q801’ s Internal Oscillator

Figure 6

Logic Circuit

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