TDA16846, its pin functions are as follows:
Pin 1: An RC network is connected in parallel with this pin to ground to determine the loop turn-off time and the operating frequency in standby mode.
Pin 2: A capacitor is connected in parallel with this pin to ground. It is connected to the primary winding of the switching transformer and the drain of the switching transistor through a resistor. The magnitude of the resistor determines the maximum output power of the switching power supply system.
Pin 3: This pin is an input pin of the error voltage amplifier and a voltage input pin across zero (the input voltage of the error voltage and zero). When the input pulse voltage exceeds 5V, the control voltage of the 4-pin is lowered.
Pin 4: This pin is the control voltage pin. It is connected to the ground with a capacitor. The capacity of the capacitor determines the duration and control speed of the soft start of the switching power supply.
5 feet: If the photoelectric sampling circuit is used to complete the error sampling, amplification, and voltage stabilization functions of the switching power supply, the output of the photocoupler is connected between the pin and the ground.
Pin 6: This pin is the input terminal of the fault comparator. If the voltage applied to this pin is greater than 1.2V, the switching power supply stops working and functions as a fault protection. If this function is not used, it can be grounded.
7 feet: This pin is the switching power supply working mode selection terminal. If the fixed working frequency mode is selected, the parallel RC network is connected between the pin and the ground. The operating frequency of the switching power supply is determined by the RC value; if the switching power supply selects the synchronous operating mode, a sync pulse is applied to this pin.
8 feet: empty
9 feet: This pin is the switching power supply reference voltage - 5V output pin.
10 feet: When the voltage is higher than 1.2V, enter the protection.
Pin 11: This pin is the primary voltage input check pin of the switching transformer. The positive voltage of the primary winding is applied here through the resistor divider. When its divided voltage drops to 1V, the switching power supply is turned off.
12 feet: grounded.
Pin 13: This pin is the switching power supply circuit switching pulse signal output terminal, which is connected to the control gate of the switching transistor through a series resistor.
14 feet: Connect the power supply voltage and the starting capacitor. When the switching power supply is started, the power supply voltage is generated by the control winding of the switching transformer and is formed by applying a rectifying and filtering circuit.
Serial number function DC voltage (V)
1 ringing suppression time and standby frequency 2.8
2 Limit the analog current of the primary winding of the power supply 1.6
3 adjustment and zero-crossing input 2.4
4 Determine the soft start time and control speed 3
5 optocoupler input 3.7
6 error comparator 2 (V6>1.2V stop vibration) 0
7 RC oscillator or sync signal input 5.2
8 empty foot 0
9 reference voltage and current 5.2
10 error comparator 1 (V10>1V stop vibration) 0
11 primary voltage detection, V11>1V stop vibration 3.2
12 ground 0
13 drive output 2
14 supply voltage 12
The TCL color TV part switching power supply adopts the new switching power supply control chip TDA16846. It has an independent oscillating circuit inside, and its oscillating frequency has fixed mode, free adjustment mode and synchronous mode for design selection; there are various protection functions such as overcurrent and overvoltage; two voltage regulator control input terminals and two are provided. Road fault detection terminal.
Starting oscillation principle
(1). After the power switch S801 is turned on, the 220V AC point is rectified by D801~D804 bridge, and C809 (220u/400V) is filtered to obtain DC voltage of about 300V, one pass through the 3~1 winding of the switching transformer T801. The D pole of the field effect switch Q801 is turned on, and the other circuit is stepped down by the start resistor R807, and then the internal power supply terminal 2 of the IC801 enters the internal, and the external capacitor C816 of the IC801 power supply terminal 14 is charged through the internal circuit for about 1.5 minutes. After (the length of time depends on the size of R807 and C816), when the voltage across C816 rises to 16V, the internal circuit of IC801 starts, and the pulse signal is output from 13 feet. After shaping by D807 and R808/A, the switch Q801 is turned on. Therefore, the primary 3~1 winding of T802 generates a gradually increasing current, and the induced voltage generated at the two ends of 6~8 winding is rectified by D806. After C816 filtering, it enters IC801 from 14 feet to maintain the power supply of IC801 to replace 2 The start of the foot is powered. At the same time, the 2 pin pulls the voltage below 2.0V under the control of the internal circuit.
(2). At the time of starting up, since the secondary power supply branches are in a state of high current charging, the current of the whole machine is very large, and a very high anti-peak voltage is generated, and the "surge" at the time of starting up. The current or anti-peak voltage poses a great threat to the switch Q801. Therefore, the IC801 is provided with a soft start circuit composed of a 4-pin internal circuit and an external capacitor C817. When the power is turned on, the IC801's internal power supply circuit charges the capacitor C817 through the 4 pin. Since the voltage across the capacitor cannot be abruptly changed, the voltage of the 4-pin can only gradually increase slowly. This voltage is supplied to the "on-time comparator". ", it controls the 13-pin output drive pulse conduction period to gradually widen with the increase of the 4-pin voltage, so that the on-time of the switch Q801 is gradually extended, and the secondary output voltage is slowly increased to the design value. . This prevents the switching transistor Q801 from being damaged due to overcurrent or breakdown due to reverse peak voltage at the instant of power-on.
1. Troubleshooting example
[Example 1] According to the user's report, the image sound is normal when receiving the signal, but there is a burnt smell, and there is a slight "click" sound in the machine (model 2111D).
Overhaul: Turn on the power of the machine and press the second power button. After about 3 seconds, the sound and image appear. There is a “beep†sound in the auditorium. It is not the sound of the line frequency oscillation. The vertical direction is slightly distorted and the edges of the image are slightly burred. From the point of view of the fault phenomenon, the +300V filter capacitor C809 is more likely to fail. Upon inspection, it was found that the top of C809 had been cracked open, and a small amount of crystallized material was condensed on the surface, which was removed and replaced with one. Test machine, troubleshooting.
[Example 2] According to the user's response, at the moment of turning on the power, only the sound of “å±â€ is heard in the machine, and there is no movement anymore, and the power indicator light is off (model 2111D).
Overhaul: After checking, the fuse F801 is black, the switch Q801 is short-circuited, the peak absorption network C819, C818, R809, D805 is normal. After replacing the fuse and switch tube, disconnect the L802 line load, in the +B filter capacitor C823 (220u/160V) and 60V bulb load on both ends, use the voltage regulator to fill the mains to 160V and then input into the TV. Turn on the light and find that the bulb emits dark red light. The measured +B voltage is 112V. Shut down, restore the L802 line power supply, keep the 160V voltage unchanged, then turn on the power, the normal grating appears, observe more than ten points without abnormality, shut down, remove the voltage regulation equipment, directly input 220V voltage, press the power switch, about 2 seconds , the new fuse, the switch tube is damaged. For the sake of stability, the Q801 will not be installed. Turn on the power, check the voltage of pin 14 of IC801, and find that the hands can swing between 8~15V. It is suspected that the external capacitor C816 (22u/50V) of 14 feet is leaking, and the measurement is removed. No abnormality is found. Try replacing the 22u/50V electrolytic capacitors, or not. When the power is turned on, the charging current of the C816 is provided by the 2-pin external starting resistor R807. Check R807, it should be 1M, and the measured resistance is 4M, which is abnormal. Replace with a new resistor, install Q801, boot, everything is normal, troubleshooting.
[Example 3] Why does the increase in the startup resistance burn BUZ91? Because the TDA16846 has a special fault internal cause, the output of the inverter inside the IC is controlled by the IC13 pin drive pulse. When the time trigger output is low, the inverter output is high, and the voltage of the 2 pin is gradually increased. High, up to the control voltage Vcv, the ONTC turn-on time comparator flips and the switch is turned off. When the starting resistor value is increased to 4 times of its own, the time constant R807xC815 becomes correspondingly larger, and the charging rate becomes slower, resulting in longer conduction period of the switching tube, and the maximum average current exceeds the rated protection value, causing damage to the switching tube. The consequences are inevitable.
[Example 4] AT2590UBD three no, measuring TDA16846 14 pin voltage is 7V, normal is 13V, detecting 14 pin external capacitor, found capacitor C818 leakage, and capacitor C818 circuit diagram is not marked. It is normal after the replacement.
[Example 5] 2911D, the line does not start, measure TDA8841 (40) pin line excitation no output, 41 pin voltage is up to 4V, normal voltage 0.9V, check the reverse feedback capacitor C416 leakage, normal after replacement.
[Example 6] 2116E remote control failure, the character is left to shake and draw, after checking the CPU 18th pin external point capacity C034 leakage, normal after replacement.
[Example 7] 2169C There is a black band 2cm wide on the right side of the screen. After checking the 30-foot FBT pulse disappears, the phase output excitation pulse phase shifts backward, and the D381 and IN4148 diodes are replaced, and the fault is eliminated.
[Example 8] The AT2570UB grating becomes larger and smaller as the image becomes brighter and darker, and the accelerating potentiometer grating also changes. It is found that the parallel capacitor C408 (22n/250V) and the pillow diode D403 (FR104) have no capacity. normal.
[Example 9] The AT2965U machine has an automatic standby fault during the viewing process. The cause of the fault is that the transistor Q208 is connected to the diode D201 (circuit icon D210). This diode function is to provide the TDA9380 reset, which causes the D201 to be soldered on the board. There is hot melt adhesive. After the machine is used for a period of time, the hot melt adhesive is heated and expanded to pull D201 to open the weld, and an automatic standby fault occurs. Remove the hot melt adhesive, repair welding D201, hot melt adhesive.
[Example 10] 2116E power supply part IC is TDA16846
Fault phenomenon: no law three no fault reason: the multimeter only needs to contact the power supply part, and it is normal for several days. After many repairs, it is found that it is cold state, D803 (RF104) is open circuit, and the soldering iron heating test is normal, TDA16846 The movement has this fault.
[Example 11] 2975D power supply part IC is STR6708A
Fault phenomenon: Three no-light flash failure Cause: Previously Q801 (D667) is bad, and now mostly caused by D809 (RF104).
[Example 12] HID435, HID432B.R, HID438SB.R and other rear projection failure phenomena: Three no fault causes: This is because the power supply part starting resistors R8009, R8010 (270K), R8004, R8005, R8006 (360K) open circuit. And IC8002 (LM393N) is prone to failure.
[Example 13] HID2990P
Fault phenomenon: no grating at the second startup, the filament is bright. Cause: One of the two 220K resistors on the CRT board is damaged.
[Example 14] AT2970I, AT2988I
Symptom: The second is not turned on. Cause: The CPU board is broken.
[Example 15] AT270I, AT2988I
Symptom: The cold machine boot image pulls the wire. Cause: The DUY board is broken.
[Example 16] OM8838 movement failure phenomenon: secondary startup three no fault causes: row push tube collector voltage is 8V-20V, base is 0.8V, off R248, OM8838 (40) foot voltage is 7.8V, OM8838 ( 12) The foot has no voltage. Check that the L203 inductor is open.
[Example 17] OM8838 movement failure phenomenon: secondary startup without grating failure Cause: OM8838 (18) foot voltage is below 4V, check: R280 (22K), R281 (33K) has an open circuit or deterioration.
[Example 18] LA76832 movement failure phenomenon: no color failure Cause: crystal 4.43319MHZ is bad (can not use crystal 4.43MHZ generation)
[Example 19] AT2970I, AT2988I
Fault phenomenon: The button does not work. Cause: The CPU board is broken.
[Example 20] . TCL 2975D color TV grating is compressed up and down.
Test IC301 (TDA8351) nominal angle voltage field is normal, it is suspected that the IC201 (OM8838) output field sawtooth waveform has distortion check and the external circuit components formed by the sawtooth wave, and the 232 (39K) resistance value is changed to 57K. The presence of the sawtooth wave forming circuit. The resistance value of R232 directly affects the reference current value of C231 charging. R232 variable value. The linearity of the sawtooth waveform is degraded, causing linear distortion outside the grating. The grating returns to normal after replacing R232.
[Example 21] .TCL 2975D color TV, boot without grating. There is a "click" sound inside the machine.
Boot up. Press the screen button to start, and the main power supply 140V output is normal. The outer output stage emits a "click" sound.
Shutdown check Q402, damper tube D405 and the correction output stage of its components found no abnormalities. Remove C416, C417.
When the power is turned on, the raster appears and the image is normal, but there is no character display. Use the digital meter to block the detection. C416 C417 No abnormality, worrying about C416 is a high voltage capacitor, if its withstand voltage is not enough, if there is high voltage leakage after power on. Try C416,
Boot everything is fine.
[Example 22]. TCL 2975D color TV has a grating, but no character display, there is about 20MM wide vertical layer on the left side of the screen. According to the color TV principle, vertical bar interference may occur, which should be caused by abnormal operation of the scanning part. In this example, the analysis of "no characters" phenomenon, the CPU (IC001) character working condition is 23 24 pin character oscillator external LC component intact 1 2 pin has the correction field synchronization pulse input. This fault phenomenon scans abnormally, and it can be preliminarily determined that the fault point is in the correction scan output stage. The correction pulse of CPU1 pin (correction sync pulse detection) is taken from the correction tube Q402C level, C416 (470P/2KV) C417 (4700DF/250V) The voltage dividing circuit is composed of one of the two capacitors, which will cause the pulse of the 1 pin to be lost, resulting in no character display, and will also cause the scan output stage to work abnormally. CPU1 pin normal voltage is about 0.5V, measured only 0.1V
Check C417 for serious leakage, and replace the fault after replacement. The C416 C417 open circuit also receives a no-character display, but the image is normal. In addition, the Zener diode D408 (8. 2) is also easily damaged. If the breakdown is short-circuited, a black screen appears.
[Example 23]. TCL2975D color TV three no check this fault, you can first remove the I802 (TLP621), and then use a 10K resistor and connect to the I4's 3 4 feet, if the power supply can start, it indicates that the fault is in the secondary boot circuit Otherwise it should be a problem with the power supply itself. After the above-mentioned ** test machine, the power supply works normally, check the standby and the secondary start circuit and find that the IC802 is damaged, and the fault is eliminated after replacement.
[Example 24]. 2136D intelligent movement series failure: can not be turned on, the indicator light flashes, no grating maintenance: first check the power supply output voltage is normal, the action is normal.
According to the structural characteristics of OM8838, we should first consider whether the 18-pin is normal or not. The pole test current input is checked. It is found that D203 (8.2V) is damaged and short-circuited, and the 18-pin has no current input. Therefore, the OM8838 protection causes no light, no picture, no sound. phenomenon.
[Example 25]..2911DZ
Fault: burning tube.
Overhaul: check the line tube excitation voltage is normal, push the variator, push should be normal, replace C416 (470P/2KV) boot normally.
C416 is a high durability and pressure capacitor. C416 and C417 divide voltage to generate a line pulse signal. If the internal insulation is poor, the circuit will appear, so that the signal sent to the DM8838 41 pin will be normal, and the line opening time will be prolonged. Burnt out.
[Example 26] .. 2111D
Fault: three no (lights flash)
Overhaul: The main current is normal, and the voltage of each output stage is normal. Only the line of the Q401 base TV (0.4) is saturated. After IC201 (8838) 405 (560P/2KV), the power is normal.
[Example 27]: HID2988I
Fault: Black screen overhaul: Increase the accelerating pole voltage retrace line, measure the voltage of the 21st, 24th and 26th feet of KA2500 is only 0.3V, and the voltage of the three feet is 2.8V when normal. The power supply voltage and external components of KA2500 are measured. The fault of replacing KA2500 is still the same. Because the KA2500 is I2C bus control, replace the memory, troubleshooting.
[Example 28] HID435 rear projection failure phenomenon: three no, the indicator light is green.
Fault reason: This is because the power supply part protection resistor R8071 (22K) is open. Easy to malfunction.
[Example 29] AT25S135 (TCLA04V01-TO, 8803)
Symptom: The lines are not synchronized.
Fault reason: TCLA04V01-TO, 8803 pin 14 external capacitor C235 (822) leakage, this pin is a phase detector, it detects the phase difference between the line oscillation pulse and the line sync pulse, and produces an error proportional to the phase difference. The current is smoothed into a DC error control voltage by an external 14-pin filter capacitor to control the line oscillation frequency and phase. Normally, the voltage of this pin is about 6V. It is measured that the voltage of this pin is only 0.4V. After replacing the capacitor C235, the fault is eliminated.
[Example 30] HID29189PB
Fault phenomenon: pincushion distortion, line jitter.
The cause of the failure: 6888 is bad
[Example 31] AT21S135
Fault phenomenon: The lower part of the field is compressed.
The cause of the fault: HVCC voltage is only 6.2V, normal is 9.2, and resistor R235 is increased from 22K to 60K.
[Example 32] 2510G
Fault phenomenon: Black screen failure Cause: This machine adopts OM8838 (and TDA8841 interchangeable) line, which is more prone to black screen failure, mostly due to poor performance of C4544, which accelerates the leakage of the filter capacitor, such as repeatedly adjusting the acceleration potential. A normal grating can appear. The machine repeatedly adjusts the accelerating potentiometer but can not appear normal grating. The voltage of the OM8838 (50) is 4V. This pin is the UHV overvoltage protection input. The normal voltage is 2V. The external resistor R234 (27K) is measured. ) Increase to 90K, replace the resistor and troubleshoot.
[Example 33] 2510G
Fault phenomenon: Black screen failure Cause: The voltage of the 12V voltage is only 2.5V, and the sound effect processing block M62438VCC is short-circuited. After the replacement, the fault is eliminated. If there is no such integrated block, the left and right channel input and output terminals can be directly connected by wires.
[Example 34] AT2516UG
Fault phenomenon: Pincushion distortion Cause: Pillow school field effect transistor Q447 (BUK444, practical IRF630, can also be replaced by BUZ91) Source R488 open circuit,
[Example 35] AT29211, AT29228 and other models failure phenomenon: AV, TV no picture failure Cause: Resistor R939 (1M) open circuit, R939 is Q915 (A1015) base bias resistor, when R939 is open, Q915 has no base Offset and off, so that the sync signal can not be sent to the IC101 (TMPA8809) 62 pin, the CPU judges no signal and a blue screen appears.
[Example 36] Model: AT2956B (using S6708A line)
Fault phenomenon: repeated burning triode Q801 (D1273)
Fault reason: When the triode Q801 works normally, it can be touched by hand, and this machine just hot starts Q801, it is hot, and the Q801 b, c, e pole voltage is 7.5V, 65V, 7.2V, normal, try to replace D803, C808, C809 The fault remains, the voltage of the diode D805 is no voltage, the normal is 4V, the D805 is normal. Carefully observe the crack in the copper skin of the transformer T803(2), and eliminate the fault after welding.
[Example 37] Model: HID4321H
Fault phenomenon: Light flash, no power failure Cause: Measure +B voltage, just turned on to 135V, turn into zero volt after a few seconds, suspect load short circuit, short open standby triode Q8010C, E pole, screen appears in the lower half of the field No grating phenomenon, troubleshooting after replacing the field block.
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