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Jul 11, 2008, 1:53 AM
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You should measure volts with DC not AC and you don't need to turn on the tv, just plug in the cord,and measure the way i suggested.and about The CTC203 you should have like ctc203ad5/AX and so on give those letters and #,s after ctc203?????? Also look at L14401 take this coil out scrap its leggs and resolder back,also you may have to replace the hot,also check this info below. Power Supply 11 Figure 2-1, CTC203 Main Power Supply Block Diagram POWER OUTPUT Q14101 BIAS SUPPLIES OUTPUT POWER TRANSFORMER T14101 OPTO-ISOLATOR U14101 +16Vr +5.2Vs -12Vr +33Vs +7.6Vr Reg B+ Feedback Reg B+ CONTROL LATCH Q14102/103 PRECISION REGULATOR U14102 OVER-CURRENT OVER-VOLTAGE R14108 Raw B+ Cold Ground Hot Ground The main supply generates voltages for normal operation of all other circuits and components. In addition, many of the supplies are used to generate the remainder of the low and high voltages required by the chassis. The Technical Training Manual will discuss the power supplies in this order; Main, Switched (SW) and Scan Derived. 12 Power Supply Figure 2-2, Power Supply Output Device Waveforms Q14101 Drain Voltage Q14101 Gate Voltage Q14101 Drain Current Standby Supply Overview The standby supply is a new class of high power, ZVS (Zero Voltage Switching) supply developed to minimize switching losses and radiated noise. A return to discrete devices lowered parts count and decreased circuit board space utilization. ZVS refers to the ability of the supply causing the voltage across the principal power output device, to reduce to near zero before the device is switched on. Yet it has a slow enough time lag to allow the device to switch off completely before any appreciable voltage is present across the device. This can better be illustrated in Figure 2-2. Note that the first two waveforms are voltages, while the third is current. The MOSFET begins conducting current when the gate voltage reaches the proper turn on point. From that time, output current rises linearly due to the inductance of the output transformer. However, notice that once the gate voltage goes high, the drain voltage decreases almost to zero volts. This eliminates much of the heat dissipation normally required of an output device. By reducing the switching losses to almost zero, the efficiency of the power supply is greatly increased and the limiting of the switching voltages causes a substantial reduction of switching noise. Also note that by utilizing the resonant recapture of energy stored in the leakage inductance of the output transformer, neither a snubber nor a clamp is required, leading to improved efficiency and lower parts count. Power Supply 13 Digital Latches Before wading deeper into the CTC203 power supply, the technician should become familiar with the control circuitry used to turn the power output devices on and off. It will be common to various ZVS supplies used throughout this and other TCE chassis'. The control switches act similar to an SCR, but with a few variations. Figure 2-3 shows a truth table and simplified schematic representaion of the power supply control latch shown in Figure 2-4. Again, while the other ZVS supplies may have slight variations, the basic concept and operation is the same. Q1 and Q2 form the basic latch circuit. Both are switching transistors that saturate when tripped on. In this case an NPN and PNP are used to force the desired results on the output. The latch is controlled by placing or removing voltages on either base while sufficient voltage is present on Q2-E to set the latch. Keep in mind B+ will supply drive to the output when the latches are off!!! The latch REMOVES the output. Any time the truth table shows a low (0) condition, output is removed. In condition A, both IN1 and IN2 are low (0). A low in Q2-B turns it on providing a current path from B+ through R5, R2, Q2-E/C and R3 to ground. Sufficient bias is developed across R3 to turn Q1 on, setting the latch. Now, regardless of what happens on IN1, the latch is set. The combined voltage drop on R3 and Q2-E/C places Q2-E at a very low voltage, shutting the output off. If IN2 goes high (1) as in condition B, there will be no effect on the output. The high on IN2 would turn Q1 on, but since it is already on the result is no change in the output state. In condition D, both inputs are high. A high on Q1-B turns it on. When it turns on it saturates, bringing Q2-B low, turning it on. When it turns on the latch is again set and the output goes low. Condition C is the most difficult to understand because it relies on the input voltages being different before the latch is tripped. If IN1 is high, the latch state is dependant upon IN2 for its output state. If IN2 is low, the output is high. If IN2 is high, the output is low. However, if the latch is set (tripped) Q2 saturates and holds Q1 on even with IN1 high. What has to happen before the latch will trip off is the loss of bias on Q1-B. As IN2 decreases it begins to divert current flow away from R3 and its voltage drop also begins to decrease. The voltage on Q1-B will eventually drop low enough for it to shut off. If IN1 is still high Q2-B is now high and it also shuts off. This removes both Q1 and Q2 from the circuit and B+ now supplies the output voltage. Figure 2-3, Digital Latch & Truth Table R3 3300 Q2 R4 1000 R2 1000 B+ R1 1000 Q1 IN 1 IN 2 Out IN1 IN2 OUT 0 0 0 1 0 1 0 1 0 1 1 0 A B C D R5 680K 14 Power Supply Control Latch Review Now that the digital latch operation is understood, it needs to be shown how it is used to regulate the CTC203 power supply. Using the simplified digital latch schematic from the previous page, when IN1 is high, IN2 may be used to control the output. When IN2 is high, the output is low. When IN2 is low, the output is high. In Figure 2-4A, Q1-E is grounded. Normal PN junction drop of a transistor dictates that a bias of at least +0.6V must be placed on Q1-B to turn it on. In Figure 2-4C Q1-E is connected to a negative 5V supply. The current to turn the PN junction of Q1 on remains the same. Now the voltage on Q1-B need only be 0.6V higher than Q1-E, or about -4.4V. In this manner, the voltage that triggers Q1 may be varied and used to control the output of the latch. By understandby this circuit, the regulation and protection of the power supply may be more fully understood. Figure 2-4A, Digital Latch Normal R3 3300 Q2 R2 1000 B+ R1 1000 Q1 IN 1 IN 2 Out R5 680K +0.6V R3 3300 Q2 R2 1000 B+ R1 1000 Q1 IN 1 IN 2 Out R5 680K +1.0V R5 1000 Figure 2-4B R3 3300 Q2 R2 1000 B+ R1 1000 Q1 IN 1 IN 2 Out R5 680K -4.4V -5V Supply Figure 2-4C In Figure 2-4B a resistor (R5) has been placed in the emitter circuit of Q1. The resistance of R5 reduces the amount of current through the PN junction of Q1E/B with the same voltage on Q1-B. Thus, to increase current high enough to turn on Q1, Q1-B voltage must increase. In this case to about +1.0V. Power Supply 15 Figure 2-5, Power Supply Control Latch Latch Circuit Figure 2-5 is the control latch for the CTC203 power supply. It is not much different from the simplified schematic in Figure 2-3, however there are some additional circuits that will need to be discussed later. When power is first applied to the chassis, Raw B+ is available on the "IN1" line at the junction of Q14103-C and Q14102-B. Since there is no bias difference from Q14102B-E, it is off and the latch is off. Raw B+ now supplies gate drive to the output device Q14101-G, turning it on providing output transformer current. At this time, "IN1" is high, IN2 is low and the latch is off, allowing gate drive. As current builds in the output device, a voltage is developed accross R14108. When this voltage increases enough, it will bias Q14103 on, which also turns on Q14102, setting the latch. A current path now exists between Raw B+, R14103, R14106, Q14102-C/E, R14110 and a negative bias voltage developed from the output transformer. Once the latch is set, Q14102-E voltage and output drive is removed and the output device, Q14101 shuts off. With output current dropping, the corresponding voltage drop across R14108 begins to decrease along with the negative bias supply. At some point the voltage at Q14103-B drops low enough to allow it to turn off. When it does, bias is removed from Q14102-B and it shuts off. When it shuts off, gate drive is again allowed to turn the output device, Q14101 on and output current begins to build once more. As the power supply circuits develop, it will be seen that by either varying the bias voltage on Q14103-B while maintaining the voltage on Q14103-E, or varying the bias on Q14103-E, while maintaining the voltage on Q14103-B, the on/off time of the latch can be controlled precisely. Controlling the latch means output current is also controlled. The off time of the latch is reasonbly constant. It is the "on" time of the output that controls the supply voltages. CR14105 R14108 0.1 3W Q14102 R14109 750 R14107 43 Q14101 To Output Transformer T14101 R14103 1Meg R14104 3300 R14106 1000 R14110 22K Q14103 Raw B+ Positive Bias Supply IN1 IN2 OUT 16 Power Supply Main Supply Block Diagram The Main Supply distributes power to all devices that need to remain "alive" when the chassis is "off". In addition, it must retain enough power to keep the microprocessor active during a power failure event long enough to exercise the "batten down the hatches" routine leading to a graceful shutdown of the chassis before power disappears completely. ("Batten" is a software routine which stores off all customer settings and chassis alignments to the EEPROM. This enables the set to start normally after a catastrophic power failure.) The voltages available during standby operation are: • -12 volts • +5.2 volts • +7.6 volts • +16 volts • +33 volts • Reg B+ The supply converts raw B+ from the incoming AC line into the various DC supplies required by the CTC203. There is a "Data Acquisition" mode requiring greater current supply demands from the supply than normally needed during standby, but less than is needed during full run operation. For instance, during a TVGuide+ download, there is no reason for the set to display a picture, however, the tuner must be active to receive the signal. This requires more current from Reg B+ from which the +33V supply is derived. Since the forward conduction mode is used, the driver current is proportional to the supply current and higher frequencies (70-90 kHz) may be used for greater efficiency. The standby supply may be broken into several sections according to Figure 2-5. The Latch circuit (discussed previously) consists of Q14102 and Q14103. They control the off/on time of the output device, Q14101. Current in the output power transformer, T14101, transferred to the secondary, is used to generate the various supplies from Raw B+ provided by the main rectifier from incoming AC. The regulator, U14102 and opto-isolator, U14101 provide regulation of the +16Vs supply and isolation between the cold ground run supplies and the hot ground generator circuit components. Overcurrent and overvoltage protection of the output device is provided by resistor R14108 in series with Q14101. Power Supply 17 Figure 2-6, CTC203 Main Supply Block Diagram (Standby Voltages) POWER OUTPUT Q14101 BIAS SUPPLIES OUTPUT POWER TRANSFORMER T14101 OPTO-ISOLATOR U14101 +16Vr +5.2Vs -12Vr +33Vs +7.6Vr Reg B+ Feedback Reg B+ CONTROL LATCH Q14102/103 PRECISION REGULATOR U14102 OVER-CURRENT OVER-VOLTAGE R14108 Raw B+ Cold Ground Hot Ground AC Input and Degaussing Raw AC is connected using protection (F14200) and filtering/smoothing components to assure spikes and unexpected surges do not cause catastrophic failure. Degaussing may only be done when the +12V run supply is active. System Control sends a high out during startup turning on Q14201. As long as the +12Vr supply is up, relay K14201 is turned on activating the contacts on pins 3 & 4. Current from the AC line is now routed to the degaussing coil. Degaussing occurs as long as thermal resistor RT14250 allows. It provides an exponential decay of current to the degaussing coil. Degauss current must be allowed to decay before the relay stops all degauss coil current to allow proper degaussing, otherwise color non-uniformity will result. When System Control removes the active deguass signal, Q14201 shuts off, removing drive current from the relay coil, breaking the contacts and removing AC power from the degaussing coil. The degaussing cycle is then complete. RT14201 K14201 3 4 2 1 +12VrSW Q14201 CR14250 J14203 DEGAUSSING COIL From Incoming AC Line U13101 SYSTEM CONTROL 45 R14206 1000 Degauss: High Figure 2-7, Degaussing 18 Power Supply Figure 2-8, AC Input Raw B+ Incoming AC (95 - 135 VAC) is input through an LCI (Line Conducted Interference) filter consisting mainly of T14201 and several filter capacitors. Raw B+ is generated from the incoming AC by a discrete bridge rectifier circuit consisting of CR14201, CR14202, CR14203 and CR14204. Main power supply input voltage is 95-135 VAC to provide a Raw B+ voltage of about +156V depending upon the chassis version. Generally, larger screen sizes will require higher raw B+. 156VDC 120VAC Raw B+ F14201 5A TP14210 C14205 680uF C14206 0.012 To DeGauss Circuit CR14202 CR14201 CR14204 CR14203 T14201 Power Supply 19 Figure 2-9, Main Power Supply Main Supply Operation To simplify the understanding of the standby supply (shown in Figure 2-9), it will be broken down into smaller blocks. These blocks operate somewhat independently, but ultimately must all function together for proper operation of the supply. The sections are: Output Drive Control Feedback/Regulation Bias Supplies T14101 9 5 16 14 15 13 10 11 12 Q14102 Q14101 Q14103 3 8 R14107 43 R14106 2000 C14101 2.2uF CR14110 CR14106 CR14108 C14122 33uF C14122 33uF CR14107 33V C14121 3.3uF C14114 3.3uF L14102 R14124 3.3 2W Reg B+ R14109 750 R14110 22K C14108 0.047 C14104 0.047 CR14103 CR14104 R14108 0.1 3W R11513 4700 CR11504 18V Q11501 R14103 1Meg R14104 3300 R14101 47K R14102 6800 CR14101 47V CR14102 CR14105 C14108 1100 1.6KV RAW B+ Neg Hot Bias Supply Neg Hot Bias Supply Pos Hot Bias Supply Pos Hot Bias Supply R14105 10 R14113 1300 R14112 680 U14101 U14102 +16Vs CR14117 16V +33Vs +16Vs +7.6Vs +5.2Vs -12Vs -12Vr CR11505 NC U14103 +5.2V Reg +12VrSW -12V Fil C14116 R141111 47uF 10K Q14107 Q14106 R14126 37.4K CR14111 R14115 143K R14116 2000 R14127 10K R14128 680K +13Vr +16Vs RegB+Vs Feedback/Regulation Output Control Drive Bias Supplies 20 Power Supply Standby Supply Startup A voltage divider network from Raw B+ consisting of R14103 and R14107 provides the initial positive gate voltage for output MOSFET Q14101 to begin conduction. As current begins to flow in the output transformer T14101, winding 3/8, feedback current is induced to windings 1/2. This winding provides several bias voltages to the supply drivers and feedback circuit, but initially is used to increase the gate voltage, using C14101 to couple the transformer to the gate. The voltage at pin 9 is increasing in a positive direction as current increases in the primary. This rising voltage eventually causes the output, Q14101, to saturate, beginning the first cycle of operation. As current through Q14101 increases, the voltage drop across current sense resistor R14108 increases until a threshold is reached. (This threshold is discussed in the control latch section.) At the time the threshold is reached, the regenerative switch (latch circuit) consisting of Q14102/Q14103 turns on, removing gate drive from output device Q14101. Current flow through Q14101 drops quickly to zero and energy stored in the transformer primary winding is transferred to C14108 which charges with the negative potential at Q14101-D. This rising voltage appears across the secondary winding. When the secondary side of the transformer conducts, the energy stored in the primary of T14101 is delivered to the secondary supply capacitors and the load. After the secondary diodes stop conducting, energy still contained in C14108 drives the drain voltage of Q14101 toward zero. When the drain voltage attempts to go below zero, an internal diode clamps it near ground. Now the voltage of T14101 drive winding, 5/9, goes positive and if the latch circuit allows it, will turn on Q14101 and the next cycle begins. Once the initial startup pulse from Raw B+ starts the cycle, this bias supply takes over and continues to supply gate drive to the output device. Figure 2-10, Power Device Start up Current Flow Part of T14101 Q14102 Q14101 Q14103 3 8 R14107 43 R14106 2000 C14101 2.2uF R14109 750 R14108 0.1 3W R14103 1Meg R14104 3300 R14101 47K R14102 6800 CR14101 47V CR14102 CR14105 C14108 1100 1.6KV RAW B+ From Regulator Circuits Bias Supply from T14101 Windings 9/5 Power Supply 21 Output Q14101 provides all transformer primary winding drive current. It is a power mosfet which conducts current from source to drain when the gate voltage is high. Once on, gate voltage must be reduced to around zero or the drain-source current path must be interrupted to stop output current. During conduction, current flows from common (hot) through R14108, Q14101 and T14101 primary winding to Raw B+. C14108 is used to "tune" the resonant frequency of the primary for better power transfer. Normally this frequency is around 90kHz during standby and 40-60kHz during run operation. Figure 2-11 shows the driver and output voltages and a waveform comparing Q14101-D outputs in standby and run mode. As current flows through the primary, flux lines induce current flow into secondary windings 5/9, 11/12, 13/15 and 14/16. Typical AC voltages generated from the windings are shown in Figure 2-12. Figure 2-12, Typical Secondary Winding Voltages Figure 2-11, Main Supply Output T14101 9 5 16 14 15 13 10 11 12 CR14110 CR14106 CR14108 C14122 33uF C14122 33uF CR14107 33V C14121 3.3uF C14114 3.3uF L14102 R14124 3.3 2W Reg B+ R11513 4700 CR11504 18V Q11501 +33Vs +16Vs +7.6Vs +5.2Vs -12Vs -12Vr NC U14103 +5.2V Reg +12VrSW -12V Fil C14116 47uF Bias Supply Windings Q14101 3 8 R14107 43 C14101 2.2uF R14108 0.1 3W C14108 1100 1.6KV RAW B+ T14101 Pin # AC Voltage 3/8 400 p-p 5/9 15 p-p 11/12 26 p-p 13/15 35 p-p 14/16 250 p-p 22 Power Supply Figure 2-13, Main Supply Output Drive Control Standby Supply Drive To assist the understanding of the control circuit, this discussion will not take the positive bias supply in consideration at this time. Operation of the control circuit will be identical. At initial startup, R14103 provides the gate voltage to turn Q14101 on, providing primary current. As Q14101 begins to conduct, primary winding current increases, increasing voltage across the winding and inducing current flow to all secondary windings. Q14101 quickly saturates. R14108 monitors the primary winding current, which is also the current through the output device, Q14101. As this current increases, the corresponding voltage drop across R14108 increases. When it reaches a voltage high enough to turn Q14103 on, the latch "sets" stopping drive to the output, Q14101. It does this do to a current path from common through CR14105, Q14103-E/B, Q14102, R14106 the gate drive being developed by C14101 and T14101 windings 5/9. Q14102 emitter drops to a low voltage, shutting the output device Q14101 off. This cuts current flow to the primary of T14101. Without drain current, drain voltage now increases due to back EMF across the transformer windings. The secondary diodes conduct and power is delivered to the loads. C14108 helps shape the waveform, limiting conduction time as Q14101 shuts off and drain voltage is driven to zero. Two things are now happening. First, with Q14101 now off, primary current flow begins to decrease. Second, with current flow in the primary and output stopped, the voltage across R14108 now decreases below the bias point of Q14103 and it shuts off, shutting off Q14102. The bias supply developed from T14101-5/9 and C14101 now supplies gate drive and the output, Q14101 turns back on. The process now begins again. CR14105 R14108 0.1 3W Q14102 R14109 750 R14107 43 Q14101 To Output Transformer T14101 R14103 1Meg R14104 3300 R14106 1000 R14110 22K Q14103 Raw B+ Positive Bias Supply IN1 IN2 OUT Power Supply 23 Figure 2-14, Bias Supplies Bias Supplies There are two supplies generated during standby supply operation used to internally bias the control and regulation components of the supply. Both cycles of the transformer waveform are utilized to provide a positive and negative supply voltage. These voltages vary with respect to the current flow in the primary winding of T14101 but should normally be within the 5 to 10 volt range, positive and negative respectively. An unrectified pulse is used as the initial gate pulse to saturate the output device. Standby Supply Control Without some form of regulation, the power supply will quickly reach a nominal output voltage using the control circuit in Figure 2-13. Figure 2-15 again shows the control circuitry, but adding regulation to keep the output voltages from the secondary of the supply within design limits. Load variations are constant and there is the problem of loads outside the normal expected variations to deal with. The main supply is required to provide standby and run power to some circuits, further complicating load demands. All this means that the supply must be regulated and protected against overload conditions. An opto-isolator protects the "hot" primary side of the supply from the "cold" secondary side and is also used for regulation. Referring back to Figure 2-13, it may be seen that by varying the on/off time of the latch, Q14102 and Q14103, output current can also be varied. For instance, the trip voltage required to turn Q14103 on with diode CR14105 in its emitter circuit is about +1.2V. This assumes a PN junction IR drop of 0.6V for the diode and 0.6V for the emitter-base junction of the transistor. If a second diode were placed in series with CR14105, the trip voltage would now be +1.8V. (Of course, with the added IR drop of R14109, the voltage would need to be greater.) If CR14105 were removed, the trip voltage now would be lower by 0.6V or about +0.6V. Now it can be seen that regulating the output current by varying IN2 is a matter of either increasing the voltage on Q14103-B, or lowering the voltage on Q14103-E. Either method achieves the same results. This technique may be used to provide regulation of output current. Negative Supply Source (app -5 to -15V) Positive Supply Source (app +5 to +15V) To Q14101-G CR14104 C14066 0.047uF R14601 100 CR14105 C14103 0.047uF T14101 C14101 2.2uF 9 5 24 Power Supply Main Power Supply Regulation To provide regulation of the control latch which in turn varies the secondary voltages, a regulation circuit is used. Since the regulator is monitoring secondary voltages which use "cold" ground, and manipulating circuits on the primary or "hot" side of the power supply transformer, the regulator must also provide isolation. Initially, a bias voltage is set up on Q14103-B by a voltage divider network between the positive and negative bias supplies. R14112, the output of U14101 and R14111 make up this network. Since the supplies are constantly changing do to primary current, they are difficult to measure, however when operating normally the nominal voltage on Q14103-B is very close to zero. A feedback voltage, Reg B+, is used to monitor the secondary voltages generated by the main supply. If Reg B+ increases such that the junction of R14115 & R14116 rises above +2.5 volts, the internal impedance of U14102 (See the Tech Tip on this new device) decreases. Increased current through the device turns on opto-isolator, U14101 harder and the output impedance of this device decreases. This output is in the voltage divider network between the negative and positive bias supplies. As the impedance decreases, the voltage on Q14103-E goes more negative. It now takes less voltage on Q14603-B to trip the control latch to the "ON" condition. Remember that when the latch is on, gate drive is removed from the output device, Q14101, and output current stops. Secondary supply voltages begin to drop. The waveform shows voltage levels on the emitter of U14101 (Top) and the collector (Bottom). The emitter is essentially the negative supply ripple. The DC level is about -11V. The internal impedance of the output section is increasing and decreasing at such a rate that under normal load levels it fluctates closely around 0V. Figure 2-15, Standby Supply Regulation Neg Hot Bias Supply Pos Hot Bias Supply Q14107 Q14106 R14126 37.4K CR14111 R14115 143K R14116 2000 R14127 10K R14113 1300 R14111 10K R14112 680 R14128 680K U14101 +13Vr U14102 +16Vs +16Vs Reg B+ CR14117 16V To Control Q14103-E Power Supply 25 When Reg B+ drops sufficiently, the junction of R14115 & R14116 drops below +2.5V. Now the internal impedance of U14102 increases. As it increases, the output section of the opto-isolator, U14101 is driven less and its impedance also increases. The voltage on the collector of U14101 now goes towards the positive supply. This voltage is also on Q14103-E. It now takes more voltage on Q14103-B to turn the control latch off. Gate drive is allowed on the output, Q14101 and primary winding current is again available in T14101. As current in the primary increases, voltage in the secondaries also increases and the cycle repeats. If a failure occurs in the regulation circuits such that the output of U14101 opens, the positive hot supply is placed on Q14103-E. Output current is now stopped only by the overvoltage/overcurrent protection provided by R14108, which is acting as a current monitor for the output device. If the failure mode shorts U14101 output or places it in a low impedance mode, the negative hot supply, only limited by R14112 appears on U14101-C and thus Q14103-E. It now takes very little output current to trip the latch and remove output drive. All supplies will be reduced and not maintain any regulation. TECH TIP Precision Shunt Regulator The three terminal precision shunt regulators used throughout the various supplies of the CTC203 are unique devices. They may be thought of as "gated" zener diodes, or infinite gain operational amplifiers with a reference voltage tied to the negative input. In both cases, for the CTC203 chassis, 2.5V is the reference voltage. Figure A shows the regulator when the reference voltage on pin 1 is above 2.5V. The regulator conducts, its internal impedance decreases, and current through the device increases. Figure B shows the regulator when the reference voltage on pin 1 is less than 2.5V. The internal impedance of the regulator increases and current flow through the device decreases. In both cases, the current through the regulator directly drives the LED side of the opto-isolator. As this current increases, the output impedance of the opto decreases. As current decreases, the output impedance increases. U14101 U14102 R14116 2000 0.1% R14115 143K 0.1% +16Vs Reg B+ 1 2 3 >2.5 Decreased Internal Impedance Increased Current Flow U14101 U14102 R14116 2000 0.1% R14115 143K 0.1% +16Vs Reg B+ 1 2 3 < 2.5 Increased Internal Impedance Decreasing Current Flow Figure A Figure B 26 Power Supply Run Mode In order to supply the different current demands between standby and run modes, the main supply monitors the +13Vr supply generated from scan. If the supply is running, Q14107 is on, turning off Q14106. This removes R14126 from the regulator circuit and supply operates normally. When scan is lost, the +13Vr supply is removed turning off Q14107. This turns on Q14106 placing R14126 in parallel with the second regulator network resistor R14116. This effectively lowers the resistance of the pair. It takes less Reg B+ voltage to trip the latch and current in the output transformer is decreased. Figure 2-16, Run Mode Neg Hot Bias Supply Pos Hot Bias Supply Q14107 Q14106 R14126 37.4K CR14111 R14115 143K R14116 2000 R14127 10K R14113 1300 R14111 10K R14112 680 R14128 680K U14101 +13Vr U14102 +16Vs +16Vs Reg B+ CR14117 16V To Control Q14103-E For instance, during normal operation, only R14116 and R14115 are in the feedback voltage divider. If Reg B+ increases, the sample voltage at the gate of U14102 increases, output current decreases and Reg B+ begins to fall. If it falls such that the voltage divider drops below the expected voltage level, output current is increased to raise Reg B+. When the set is in standby mode, the load on the secondary supply is greatly reduced and Reg B+ tends to increase beyond the supplies ability to properly regulate it. By placing R14126 in parallel with R14116 Reg B+ can go considerably higher than its design while the sample voltage at U14102 remains the same. The result is Reg B+ is allowed to be higher than normal by a fixed percentage based on the parallel resistance of R14126 & R14116. That same percentage applies to the remainder of the secondary voltages, but since the percentage is small, their regulation will not be greatly affected. Reg B+ is not used during standby so it may be allowed to float considerably above its required voltage. In effect, the parallel resistance raises the target voltage (Reg B+) being regulated. Power Supply 27 +12Vr +9Vr +7.6Vr R14159 47 CR14115 5.6 U14104 +12V REG 1 3 2 U14150 +7.6V REG 1 2 3 R14123 470 1W R14121 1000 R14156 51 1/2W R14151 8.2 1W CR14116 9.1 ONOFF From Micro U13101-19 Q14105 Q14104 +16Vs +5Vr +3.3Vr Q14115 R14157 75 1/2W C14118 10uF U18101 +3.3V REG 3 2 1 RUN: High Standby: Low Figure 2-17, Run Supplies Run Supplies There are several supplies generated from the main supply but only required during run operation. They are shown in figure 2-17. To turn them on and off System Control sends a high to Q14105-B turning it on. That turns Q14104 on passing the +16Vs supply to the input of the main +12V regulator. The output of the regulator then feeds +12V directly to the circuits or feeds other regulators. 28 Power Supply +200Vr +23Vr T14401 FOCUS SCREEN To Beam Limiter 4 10 1/2W 20% R14701 High Voltage TO CRT ANODE TO CRT FOCUS GRID TO CRT SCREEN GRID +13Vr TO CRT FILAMENT C14703+ 47uF 250V R14702 130K 1/2W CR14702 R14509 300 2W 10% R14703 0.88(0.82) 3W R14508 1.0 CR14701 2W 10% CR14704 9 8 5 7 10 6 2 Figure 2-18, Scan Derived Supplies Scan Derived Supplies Several other sources of power must also be generated by the CTC203. They are derived from the scan circuits in a traditional way. Horizontal scan operation will be covered later. Two low voltage supplies are generated; +23V and +13V. An AC filament supply for the CRT is taken from the same winding. The CRT drivers require a higher voltage than can be generated by the normal supply. It is generated here and is about +200V. It is slightly unique as it is derived from the primary windings of the horizontal output transformer, not the secondary. The remainder of the scan derived supplies are used to power and control the CRT. They are the anode, focus grid and the screen grid supply. Power Supply 29 When output MOSFET Q14101 fails, it is a good idea to replace the latch transistors, Q14102 & Q14103. Unexpected excessive current may damage these transistors and other components in the immediate area. TECH TIP T14101 9 5 16 14 15 13 10 11 12 Q14102 Q14101 Q14103 3 8 R14107 43 R14106 2000 C14101 2.2uF CR14110 CR14106 CR14108 C14122 33uF C14122 33uF CR14107 33V C14121 3.3uF C14114 3.3uF L14102 R14124 3.3 2W Reg B+ R14109 750 R14110 22K C14108 0.047 C14104 0.047 CR14103 CR14104 R14108 0.1 3W R11513 4700 CR11504 18V Q11501 R14103 1Meg R14104 3300 R14101 47K R14102 6800 CR14101 47V CR14102 CR14105 C14108 1100 1.6KV RAW B+ Neg Hot Bias Supply Neg Hot Bias Supply Pos Hot Bias Supply Pos Hot Bias Supply R14105 10 R14113 1300 R14112 680 U14101 U14102 +16Vs CR14117 16V +33Vs +16Vs +7.6Vs +5.2Vs -12Vs -12Vr CR11505 NC U14103 +5.2V Reg +12VrSW -12V Fil C14116 R141111 47uF 10K Q14107 Q14106 R14126 37.4K CR14111 R14115 143K R14116 2000 R14127 10K R14128 680K +13Vr +16Vs RegB+Vs Figure 2-19, Main Power Supply (Repeated) Replace all on any Output Device Failure 30 Deflection Deflection Overview The CTC203 deflection circuits are very similar to previous TCE core line chassis. Some models will have pin-corrected yokes, while others use an active pincushion correction circuit. XRP is the same as previous chassis and other CRT control and protection is also similar. The horizontal deflection system has two primary functions in the CTC203 chassis. First, it supplies the current for the horizontal yoke coils providing energy necessary to move the electron beam horizontally across the face of the picture tube. Second, it provides a number of voltage supplies needed for operation of the CRT and deflection. Horizontal yoke current is provided by a circuit consisting of a switch (HOT), the primary inductance of the Integrated High Voltage Transformer (IHVT), a retrace capacitor, trace capacitor (S-Shaping capacitor), and the horizontal yoke coils. Voltage supplies provided by the horizontal deflection system are derived from secondary and tertiary windings on the IHVT. The supplies are used by the video amplifier (kine drivers), tuner, CRT, and the vertical amplifier. Low level signal processing circuits for the horizontal deflection system are contained in the T4-Chip. These include the horizontal sync separator and a two-loop horizontal AFPC system. The T4-Chip allows bus control of several parameters associated with the horizontal deflection system. These include horizontal drive pulse width, AFC Gain, Sync Kill, and ON/OFF. Enabling or disabling the horizontal drive signal from the T4-Chip determines whether the chassis operates in the Standby or Run mode. In the Standby mode, no IHVT-derived supplies are present reducing standby power requirements. The vertical deflection circuit in the CTC203 is a linear amplifier DC coupled to the vertical yoke coils. The circuit is similar to the CTC197 vertical circuitry. The vertical ramp is generated in the T4-Chip. Vertical size, bias, S-Correction, and linearity adjustments are done in the T4-Chip via the IIC bus. Timing information for the ramp generator is derived from a digital vertical countdown circuit, resulting in excellent interlace performance. The vertical output stage includes an integrated circuit containing the power amplifier, vertical flyback generator, and thermal protection. Deflection 31 Deflection Basics This discussion will only touch on horizontal, (right-left, left-right) deflection of the electron beam across the face of the CRT. Vertical, (up/down, down/up), deflection occurs in a similar fashion, just a different direction on the screen. Although there is only one horizontal yoke winding, it is wound in such a fashion that current in one direction drives the beam away from center to the left side of the screen, while current in the opposite direction drives the beam away from center to the right side of the screen. The strength of the current determines how far from the center the beam is deflected. Deflection is accomplished by forcing current through the deflection yoke, creating an electromagnet from the yoke windings that either push the electron beam away from or allow it to drift back to the center of the screen. If there is no yoke current, the beam remains center screen creating a vertical line very close to the physical center of the CRT. Figure 3-1 and 3-2 show the electron beam position at various yoke current values, assuming a static DC current from a power supply is used. (These values are only for discussion and demonstration purposes. Actual yoke current and direction for exact beam positioning will be different.) Note that as yoke current increases towards a higher positive value, the beam is driven farther towards the right side of the screen. As the positive yoke current approaches zero, the beam is closer and closer to center screen. Center of Screen Electron Beam Position +2A +4A +6A +8A +10A Figure 3-1, Electron Beam Position with Positive Current Center of Screen Electron Beam Position -10A -8A -6A -4A -2A Figure 3-2, Electron Beam Position with Negative Current As yoke current reverses, the beam is again driven away from center screen, but now in the opposite direction. The higher the negative current, the farther from center screen the beam is driven. As negative current decreases, the beam moves back towards center screen. 32 Deflection Center of Screen +Max -Max Zero Decreasing Yoke Current Now Allows Beam To Move Back To Center from Right Electron Beam Travel +Max -Max Zero Center of Screen Yoke Current now Reverses and Begins Increasing, Driving Beam to Left Side of Screen Electron Beam Travel +Max -Max Zero Center of Screen Decreasing Yoke Current Again Allows Beam To Move Back To Center from Left Electron Beam Travel Center of Screen +Max -Max Zero Increasing Yoke Current Drives Beam Away from Center To Right Side of Screen Electron Beam Travel Figure 3-3 shows how increasing positive current drives the electron beam towards the right side of the screen and increasing negative current drives the beam towards the left side. The amplitude of current drives the beam farther from center screen. (The scope captures are not in exact time alignment with the electron beam.) Again, the theory of positive and negative current flow is not important to this discussion. The concept of yoke current flow one way making the beam travel one direction, while yoke current flow in the opposite direction makes the beam reverse its travel is the point. Figure 3-3, Beam Travel Inductive Current Flow Among the many theories of deflection, yoke current versus yoke voltage is one of the most misunderstood by technicians. A yoke is simply an inductor constructed to induce its developed magnetic flux in a specific pattern around the bell of a CRT. The flux becomes stronger as current through the wire is increased, and weaker as it decreases. Figure 3-4 compares voltage across a yoke winding with the resulting current through it and magnetic field developed by it. As voltage is first applied, the yoke tends to "limit" current flow. Even though maximum voltage is immediately available, current builds slower as a result of inductive reactance. As current builds, magnetic flux fields emanating from the yoke grow stronger. When voltage is removed, the yoke tends to continue current flow as the flux fields (with no current flow to sustain them) begin to collapse. As they collapse, current decreases and the magnetic field grows weaker. If voltage is not reapplied, the current will fall to zero. The yoke is not directional. If the opposite polarity voltage is applied, the same current pattern is observed, only in the opposite direction. Time Volts Current Flux Strength 0 0 0 Yoke Winding Voltage Figure 3-4, Yoke Current versus Applied Voltage Deflection 33 19 38 Phase Detector Loop Filter 32 fH VCO Divide by 2 2nd AFC Ramp Generator Horizontal Phase Duty Cycle Control Horizontal Drive Horizontal Output H Lock Detector To Countdown Circuits Y IN Part of T4 Chip U12101 24 23 22 Horizontal Output Flyback Pulse X-ray Protect Horizontal Ground 21 Horizontal AFC Filter Divide by 16 Sync Separator Figure 3-5, T4-Chip Horizontal Deflection Low Level Horizontal Deflection The T4-Chip employs a two loop horizontal AFC system. The first loop is used to lock an internal 1H clock to the incoming horizontal sync signal derived from the baseband luma signal. The second loop is used to lock the 1H clock to a feedback pulse derived from a secondary winding on the IHVT. As with the other T-Chip versions, a horizontal to video phase control is available via the IIC bus. The phase control can be used as a horizontal centering control during alignment. The first loop employs a 32H (32 times the horizontal frequency) VCO referenced to a 503 kHz ceramic resonator. The output at U12101-22 is shown. Figure 3-6, U12101-22 Output Waveform 34 Horizontal Deflection Low Level Signal Generation The low level horizontal waveform generated from the T4-Chip has all correction signals added prior to the output from U12101-22. The horizontal driver circuit serves as an interface between the low level horizontal output of the T4-Chip and the high power horizontal output circuit. The driver operates in a "flyback" configuration storing energy driver transformer, T14301, during the conduction cycle of Q14301. When Q14301 turns off, stored energy is dumped into the base of Q14401, the horizontal output transistor (HOT). A buffer stage has been added to reduce the amount of current that must be handled by the T4-Chip horizontal output stage. This buffer consists of Q14302 and its associated circuitry. The horizontal drive waveform app
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