JVC Television Power Supply Training

JVC Television

Power Supply Training

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TELEVISION

After this course, you will learn:

• The operation of Switching supplies

• Details about the regulator IC

• Operation of the Power Supply Modes

INTRODUCTION

• The operation of the Power Factor Circuit

• Troubleshooting procedures useful in diagnosing defective components

• Some failures and their symptoms

TELEVISION

AGENDA

• Model Identification

• Service Manual Supplements

• Switching Power Supply

• Power Supply Components

• Basic Switching

• Switching Device

• Switching Operation

• Switching Review

• Power Factor circuit

• Troubleshooting techniques

TELEVISION

MODEL IDENTIFICATION

• Prior to service, it is always wise to verify the Model and Version to ensure that the correct Service manuals and Schematics are being used.

• In some cases, the Version may indicate PWB or CRT differences

• This information is listed in the Main Difference List of the Service Manual, or the Service Manual Supplements. For example YA319 is the service manual, but YA319B would be a revision.

• The Example shows that the AV-32MF36 has (4) versions. The example shows the “Z” Version of this model.

• The Model Number listed at the top of the model label will always be the same for all versions.

• The TV Model Version is usually shown to the right of the Serial Number on the Model Label

TELEVISION

SERVICE MANUAL SUPPLEMENTS

Original Service Manual

Service Manual Supplement

Supplements show Corrections, Additions and Differences that may have occurred during the production of a TV Model.

Picture tube of AV-48P776/H was changed. Therefore, this service manual describes only the items which differ from those of the AV-48P776/H service manual. For details other than those described in this manual, please refer to the AV-48P776/H service manual (No.YA318, 2005/11).

No. YA318B

2006/6

• Some Service Manual have Supplements

• Supplements show Corrections, Additions and Differences that may have occurred during the production of a TV Model.

• It is necessary to ensure you have all Service Documents for a model prior to servicing.

• The Original Manual will only show the original Service Information for a model, but Service Manual Supplements may list information that is important to the service of a model.

• Ensure that you use the Model and Model Version when looking for documents on ISee to ensure you are getting the correct information.

TELEVISION

When troubleshooting it is necessary to use the respective ground of the device you are measuring.

SWITCHING POWER SUPPLY

LIVE

Taken from Schematic 52004 Main PWB

ISOLATED

• This is the Power Section from the AV-32F703 taken from the 52004 Schematic of the Main PWB.

• On the schematic, there a BLACK ISOLATED sides of the PWB. Components on the left side are live. Those on the right side are isolated

• When troubleshooting it is NECESSARY Live or Isolated, of the device you are measuring.

• Additional components, located along the dotted line, ensure circuit isolation while passing all Power or Control signals. These components are the Relay, Switching Transformer, Photocoupler and the Capacitors that are used to connect the Live and Isolated grounds.

line that separates the LIVE and

to use the respective ground,

TELEVISION

POWER SUPPLY COMPONENTS

1. F901 and VA901 Surge Protection

2. T951, D954-57 and C951 Standby Power

3. C901, C902 and C903 Line Filter:

4. D901 and C907 Main rectifier

5. IC911 Switching Regulator

6. D911, R911,R930 and C914 Startup

7. T921 Switching Transformer

8. R912, R913 and R914 Current Feedback

9. R915 and D912 Run DC

10. D917 and D914 Refresh

11. D945 ~ RY951 Main Relay

12. Q951 Main Relay Drive

13. IC921 Error Amp

Schematic 52004 Main PWB

• Reference Schematic 52004 Main PWB for Schematic Details.

• This is a brief explanation of the components that make up the Power Supply and there functions.

• This is the basic circuit configuration and use for all JVC Power Supplies. While some Power

Supplies may omit or add circuits, the general function of all JVC Power Supplies are the same.

1. F901 and VA901 Surge Protection: Stops circuit function if High Current (short) is detected.

2. T951, D954-57 and C951 Standby Power: Supplies Standby DC voltage to Micon

3. C901, C902 and C903 Line Filter: Filtering of AC line noise

4. D901 and C907 Main rectifier: Provides rectified DC to Switching Regulator and Switching Transformer.

5. IC911 Switching Regulator: Regulates Switching Voltages out of Transformer

6. D911, R911,R930 and C914 Startup: Provides Startup DC for Switching Regulator until Transformer

conduction begins

7. T921 Switching Transformer: Provides voltages to all circuits

8. R912, R913 and R914 Current Feedback: Provides current feedback to Switching IC to stop conduction.

9. R915 and D912 Run DC: Provides additional DC to Switching IC

10. D917 and D914 Refresh: Provide Refresh voltage to Restart IC Regulation

11. D945 ~ RY951 Main Relay: Allows Power flow to Switching IC and SW Reg. Also functions as relay for Degauss

12. Q951 Main Relay Drive: Controls function of Main Relay

13. IC921 Error Amp: Monitors B1 Line Voltage

TELEVISION

BASIC SWITCHING

INDUCTOR CHARGING

1. Switch SW1 off

2. Apply a DC to the inductor as shown

3. Turn SW1 on and the Current rises slowly

4. The Inductor charges to its maximum

5. After charging is complete, the current stays constant

• One of the important part in SMPS is the Transformer. Transformer functions like a basic inductor.

• With a DC applied to an inductor and connected to ground through a resistor, if the switch is turned on, the current will rise slowly through the inductor and the resistor.

• The current ramps up and Reaches maximum and stays constant.

• When the current does not change any more, the inductor is fully charged.

• Capacitors and inductors behave similarly but opposite. Capacitors can hold the charge, but inductors can not. It has to be discharged. If there is no path to discharge, it will make eddy current through the coil and produce heat.

• The basic of Switching power supply is the effective and controlled use of using the discharged energy.

TELEVISION

HEAT

BASIC SWITCHING

INDUCTOR DISCHARGING

Once the Inductor is finished charging,

HEAT

turn SW1 off.

1. What happens to the charge in the inductor? It will be lost as heat.

2. Can we use this energy? If so, how?

3. Can we control this charging? If so, how?

This can be applied in the Switching Power supply.

• When the current flow to the Fully Charged Inductor is interrupted by closing SW1, the stored energy is released as Heat.

• This stored energy is utilized in the Switching Power Supply.

TELEVISION

BASIC SWITCHING

TRANSFORMER OPERATION

ENERGY

If there is a secondary winding during the off time, energy will be transferred into the secondary.

In other words:

Transformer charges during ON-time.

Discharges during OFF-time

If the coil has a secondary winding and a load is attached, it is called a transformer

because it transforms the energy into electrical energy and delivers it to a load.

In other words, the transformer discharges its stored energy into the secondary.

Repeating these actions again.

1. When the Switch is turned on the primary charges.

2. When the Switch is turned off, the charged core of the inductor discharges into the secondary.

3. Since we are interested in DC output, the addition of the Diode and Capacitor at the secondary will allow for the energy to be stored in the Capacitor. This stored energy is our Secondary DC voltage.

4. If the switch is turned off prior to fully charging the inductor, the transferred energy will be less. This shows that by controlling the Switch’s on/off time we can obtain necessary secondary voltage.

The Transformer, Switch or any Switching Device and a Control Circuit (to

control on/off switching) make up a Switching Supply.

TELEVISION

1. Apply an unregulated DC Voltage to the Transformer’s Primary.

2. Switching the Primary ON and OFF will result in Secondary Voltage.

3. Controlling the ON/OFF timing of the Switching Device will result in a Regulated Secondary Voltage

BASIC SWITCHING

SUMMARY

Switching power supply regulation is achieved by controlling

the switching device’s ON/OFF timing .

TELEVISION

SWITCHING DEVICE

• STR-Fxxxx IC

• Very reliable construction

F6xxxx

OVP

TSD

OSC

DRV

STR-

GND

VCC

Ocp/

• All in one package

• Protection circuits

• Minimum pins (5 pins)

• This is one of the various types of Switching Devices

used in JVC Power Supplies.

• In the previous explanations we called it SW1. On the Schematics previously outlined it is the Regulator

• It has the actual ON/OFF switch (a Power FET), control circuits, and protection circuits.

The Internal Circuits of the other Switching Devices used by JVC may vary, but

the operation of the Device is the basically the same for them all.

TELEVISION

SWITCHING DEVICE

V IN

Properties

• 0.7V Applied to Pin 1 will turn OFF the FET

Start Up

Pre Reg

T.S.D

LatchOVP

Osc.

Ref2

DRV

Ref1

OCP/FB

GND

• FET will turn on after pre-determined time

• Applying a 2.0V pulse to Pin 1 refreshes the IC prior to pre-determined time

• When a Start up DC is applied to the other circuits inside the IC, it turns the FET ON.

• When the FET is ON there will be a short between pin2 and pin3 of the IC.

• If 0.7V is applied at pin 1, the FET turns OFF. Due to the internal timing circuit, the FET will start again after a pre-determined time.

• If we wants to turn ON the IC prior to the internally decided time, we can apply a 2VDC to pin1.

• This means, we can turn ON the FET and turn OFF the FET at any time we want.

TELEVISION

V IN

SWITCHING DEVICE

Internal

Start Up

Pre Reg

T.S.D

LatchOVP

Osc.

Ref2

DRV

Ref1

OCP/FB

GND

Startup: When we apply approximately 12V to pin4, the IC’s internal circuit functions and turns ON the FET

Drive: When the internal circuit is turned on, the driver circuit turns ON the power FET

Power FET: This is what we previously called the Switch. We use this to allow current to flow

through the transformer.

Oscillator: The IC has an Oscillator for timing control. This oscillator decides its natural on/off time. This means, after applying the startup DC, after a pre-determined time it will come on.

OCP/FB: This is the control input to override the oscillator’s timing. By applying a 0.7V to this input, we can turn OFF the internal circuit and FET. By applying a 2.0V pulse, we can turn it back ON.

TSD: Thermal Shut Down: This is for the thermal protection. When the IC overheats, this circuit turns off the IC and latches it. We have to unplug the power to restart.

OVP: The OVP circuit monitors the startup DC. If the voltage exceeds the specified level, it turns off the IC and latches it. We need to unplug the power to restart. Latch: This is the latch circuit that latches and holds the shut down circuit outputs.

TELEVISION

SWITCHING DEVICE

Turn ON

D901

• Apply power to the IC

D901

D911

C914

• When the tank Capacitor charges up to the Start-up voltage, IC starts conduction

R911/ R930

• The Switching FET turns ON

• Now it can switch the RAW-DC through the Transistor, if it is connected

Reference Schematic 52004 Main PWB for Schematic Details.

• This is start up circuit. This circuit composes R911, R930, D911 and C914.

•This circuit Provides the Start-up Voltage for the Switching IC911

•The DC voltage supplied by this circuit turns the IC and FET ON.

•If the IC was open and AC current was allowed to flow, no current would flow through the IC. This would cause C914 to overcharge and explode. For this

reason, If you find a defective Switching Regulator IC, replace the Capacitor. Similarly, if you find exploded Capacitor, replace the IC.

Reference Schematic 52004 Main PWB for Schematic Details.

TELEVISION

SWITCHING DEVICE

TRANSFORMER CHARGING

C907

T921

• Current flows through the transformer and charges it

• A proportional voltage develops at

R912 R913

the source resistor

• Turning the FET off will cause the switching action

Reference Schematic 52004 Main PWB for Schematic Details.

• Once the startup DC is applied, the FET can turn ON

• The Transformer is allowed to charge.

• Raw DC is passed through the primary of a transformer to the IC pin 3

• The Voltage passed through the FET connects to a source resistor on pin2 to ground.

• As the Transformer charges, a proportional voltage will build on the Source Resistor R914.

TELEVISION

SWITCHING DEVICE

V IN

Start Up

Turn Off 1/2

• Applying 0.7V to Pin 1

LatchOVP

DRV

will turn OFF the FET

Pre Reg

T.S.D

OCP/FB

Osc.

Ref2

Ref1

GND

Do you remember this?

• FET will turn on after pre-determined time

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