AK37 Vestel Chassis Outline
Objectives
Familiarity
Chassis Outline
Operation
Areas
SMPS Standby/Normal modes
Micro Control
Signal Audio/Video and Line stage
Practical Session
Applying techniques
Stepping back
Asking questions
AK 37 Chassis Design Characteristics
Low component Count
Power Saving SMPS using Greenline PSCIC
Micro Control via IC2 data Bus
Easy Navigation customer menus
Multi Standard Capability (Option)
Platform Built for Expansion
AK37 Chip Set
MC44608/40 SMPS Control IC
ST92195 (D1 or D7) Micro/Text integration
24C08 8K EEPROM or NVM
STV Frame drive
TDA7269A 14 Watt of Audio Per Channel
STV5112 CRT RGB Drive
MSP3411G Multi Sound Processing
STV2248 Video Processor/Hrz Ver Drive
Power Supply
The AK37 utilises the latest in power saving technology by using the MC44608 Greenline power supply controller.
Feedback from secondary is provided and isolated by IC801 Opto.
Used in conjunction with TR802 (SMTX) this provides isolation from Primary and Secondary windings
Start Up, feedback and OC
Pin 8 is used for the initial start up. Its high voltage and low current Average readings are 220v at 8 a.
This is the very first action taken before the SMPS begins to operate
Once pin 8 reaches its required value, drive then appears on Pin 5 to switch the Power Fet on. This then magnetises the SMTX.
D893 & D892, provides a 1.2-volt limit by using them in series to prevent internal damage to the IC should an overcurrent event take place.
RB34 & RB07 connected in Parallel are low value to allow the Fet to switch efficiently but also allow a potential difference to be produced and provide feedback to pin 2.
These are fitted to provide OC protection from excess drive to the FET and causing catastrophic component failure.
These can fail if there is a failure of the FET or SMPS IC due to Excess current demand that the PSCI has not been able to prevent
Once the magnetism is built up, Pin 6 VCC becomes high the then sits above 6.5v and below 10. (Working range)
The unsmoothed supply which feeds the VCC voltage is used for demagnetisation information on Pin 1. This is to prevent over saturation of the SMTX
Feedback is now produced by monitoring the HT line 150v and the 16v line through IC801 Opto.
Opto Coupler
Pin 1 of the Opto is connected directly to the 16v line.
Pin 2 of the Opto is connected to QB04 to provide Standby control and IC818 ( Shunt Regulator) to provide Ht feedback.
Pin 3 of the opto is connect to Pin 3 and provides Control In information
Pin 4 of the opto is connected to the VCC line.
Standby Control
In normal running IC801 is providing feedback to keep the HT rails at there set values.
However we can use this arrangement to change the preset HT which was set at VR800 /IC818 by increasing the current through the LED in IC801. This is Simply done by switching on QB804.
The effect this has is to decrease the potental difference between Pin 2 of the opto and Ground.
However because the rails are now very much lower than their normal values the 5 volt rail must be supplied from another winding on the SMPS
Just after standby is initiated the feed to the 5 volt rail is switched to the winding which was origonally supplying the main 150V rail, now running at approxamatly 10% of its normal value. This is done by QB02 and D889.
This method is particulaly successful in power saving as you are using the abilitys of the SMPS and also the prevent the need for another SB supply.
Over Voltage/Current problems
Over voltage and Current situations are what we should avoid at all costs, However to do this there are a number of areas which we need to address.
Quick Response to Over Current/Voltage
Feedback from various secondrys
Protection against failure of other components
Carfully choosen as not to interupt normal running
Primary/Secondary sensing
Pin 2 is used for detecting over current being drawn by the FET
Could be caused by Short Line Output etc..Loptx
Pin 8 is used for over voltage from the SMTX and will shut down and Latch
Faulty opto coupler or feedback failure
Pin 3 is used for control and feedback of HT and secondary conditions.
Varying voltage i.e. Beam Current, Audio demands etc low mains!!
Again these are the steps which this SMPS takes
1. Pin 8 becomes High
2. Safety logic is established (I sense, Demag etc)
3. Drive starts at pin 5
4. The Fet switches on
5. Magnetism is induced in the SMTX
6. Supplies start to rise on secondary.
7. VCC voltage appears on pin 6
8. The opto starts to conduct and regulates Secondary Voltages Via Pin 3
9. Pin 1 feeds back to control over saturation
10. Now its in a steady running state Feedback loop is maintained
So what we have is
Over current protection X1 (I Sense)
Over Voltage Protection X3 (16V, 150Ht line and VCC pin)
Power Saving 2 modes Standby and Normal
Micro Processor Control
The Ak37 chassis uses the IC2 data bus for control of IC s throught the Tv set.
Items which are sat on the Data bus are
1. Frame Chip
2. Multi Sound Processing
3. Video Processor
4. Tuner
5. EEPROM (NVM)
6. MICRO (Incorperating Text)
The micro also has a 7-page fast text memory shown as a D7 printed on the micro, also there is a 24C08 EEPROM for storage of Options, Tuning, Height etc.. This will store data for 40 years (or so its stated) without loss of data.
Power up Procedure and Program Run
As with most micros used in day to day equipment, the VCC voltage needed to be 5v Dc which arrives from Q??? 5 volt reg.
The reset line is held low until the 5-volt line becomes available for approximately 50ms then is raised to 5v. This ensures that the program which the micro is running is executed correctly.
At this point the I2c bus is dormant as there are no requirements for data transfer from various Ic s
**Points to be aware of with the running of the micro are as follows.
The set will come on without the eeprom being fitted
The data rail does not need to be connected to allow the unit to run.
If the Data to the eeprom is Shorted together the micro will bring the set out of standby for 3 seconds the shut the set down
There is no Self diagnostic page