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Konka TV Common Faults and Cases
1, fault view: three no, indicator light is not bright.
Analysis and Maintenance: The power-on indicator does not light. Pressing the panel keys and remote control buttons will not work. This indicates that the whole machine cannot work. Analyze the cause and think that it is caused by an abnormal power supply.
First, the 12V output of the external power adapter was measured. It was proved that the root cause of the fault was that the entire device did not work due to damage to the adapter. Try to adjust its own power supply to 12V, for the LCD TV power supply, boot everything is normal, further shows that the TV is normal.
The power adapter was disassembled, and the power supply module on the circuit board was visually cracked. The plastic cover of the surface of the 300V filter capacitor had also fallen off, and the fuse was severely blackened. The 300V starting resistor measured on the road has also been opened.
Replace the original STR-G5653 replacement power supply module, substitute 100uF/400V capacitor for 300V filter capacitor, replace the original damaged part with 2A/250V fuse, replace the original starting resistor with two 180k Ω/0, 5W flame retardant resistors , and then re-test in the road resistance, no exception, before power, in the 12V output termination of a 10Ω / 15W wirewound resistor for false load, after booting, measured 12V output is normal, indicating that the power supply has been repaired. After switching on the LCD TV, the picture and sound return to normal.
In order to effectively protect the LCD TV from overvoltage, it is recommended to install a 360V varistor between the fuse of the power adapter and the rectifier bridge of the 300V rectifier to prevent damage to the TV due to overvoltage.
2, the phenomenon of failure: image, sound, brightness, sometimes there is no time.
Analysis and maintenance: According to the phenomenon of the image, sound, brightness, and sometimes there is no phenomenon, indicating that there is a serious bad contact phenomenon.
If such failures are not eradicated, it is easy to cause premature aging or damage of the LCD screen or backlight. First, the power supply adapter 12V voltage output is normal, remove the boot shell, starting from the power manager to check, when visually measured 12V connection socket J900, found that there are obvious oxidation of the three pin surface, then the socket welding With a hacksaw blade, the surface is scraped with tin, soldered into the circuit board, and then the solder is applied to the leads to prevent oxidation and recurrence. After this treatment, no such failure occurred in the TV.
3, the phenomenon of failure: In the process of watching television, suddenly found a strange smell inside the machine.
Analysis and Maintenance: According to the phenomenon that the machine emits odor, it is inferred that the temperature rise inside the machine is too high, resulting in some components on the surface of the plastic cover heating or short-circuit components.
Quickly shut down, cut off the power, disassembled and found traces of breakage in the printed board of the power manager. After careful inspection, it was found that the plastic cover on the surface of the C900 (470uF/25V) had also been deformed, and immediately touched the surface of the C900 with fingers, feeling that there was still temperature remaining. (Normally, there is no temperature rise on this capacitor surface). Suspected that this capacitor has been broken through the short circuit, measured on the road to the end of this capacitor is OΩ, after welding it down, re-measure printed board capacitor pin solder joints at positive and negative resistance of about 1200Ω.
Re-test C900 capacitor has indeed penetrated the short-circuit at both ends, with an imported high-quality capacitor substitution, and repair the printed board fracture, and then test the power adapter 12V is also normal. Turned on, the TV returns to normal.
4. Failure phenomenon: Pressing the panel keys and remote control buttons will not work, and the whole machine cannot work normally.
Analysis and maintenance: power on, carefully observe, LCD screen is slightly bright, the indicator light is normal, indicating 12V voltage is normal. According to the working principle of the television, it can be seen that such failures are caused by the MCU control circuit or abnormal power supply and loss.
After dismantling, first measure the MCU pin (44) voltage is 4,7V (normal should be 5V), continue to check the power manager 12V input is normal, turn off the road test (44) pin voltage is 5,08V, the whole machine All functions are restored.
After the user understands, this machine has failed to repair others before it caused the failure.
5, the phenomenon of failure: TV / AV status images, sounds are normal.
Analysis and Maintenance: When the PC VGA signal is input, the image appears to roll up and down (similar to a serious field out of sync).
Analysis and Maintenance: According to the working principle of LCD LCD TVs, there are two possibilities for such failures. The first possibility is that the PC field frequency is set too high, and the second possibility is that there is a fault in the computer.
First, bring up the menu and find that the field frequency is set at 60Hz (no abnormality). Then observe the U400's (68) foot field sync pulse waveform as 3, 5Vp-p (normal is about 4, 2Vp-p) with a 100MHz dual trace oscilloscope. ), suspected U400 internal damage, the principle of easy maintenance after the first easy to read, shut down after power off for 20 minutes, with a pine perfume around the U400 smear it again, and then use electric hot air gun to blow it, until the circuit board components After being naturally cooled, the camera is turned on again, and as a result, the above-described image roll-over phenomenon no longer occurs in the television. Observe the U400 (68) pin waveform with an oscilloscope, and it has returned to the normal 4 or 2Vp-p.
6, the phenomenon of failure: TV / AV state image, sound normal, when the input PC VGA signal, the image level interference.
Analysis and Maintenance: Due to the experience of overhauling, when troubleshooting, analyze the cause of the fault is similar to it, first habitually observe the U400 (68) pin waveform with an oscilloscope, the inspection found that the reading is 4Vp-p, and normal 4, 2Vp-p does not have much difference, so shut down and power off, about 20 minutes later, ready to blow with electric air gun.
After applying a layer of pine perfume around U400, it is evenly blown with an electric heat gun. After the standby device is naturally cooled, the power-on and power-on failure remains. Replace the U400 first (178) and (179) feet with an external 24MHz crystal oscillator. .
After a lot of verification, it was finally determined that the U400's VGA interface internal circuit damage. After trying a new GM5010 replacement, the fault was completely eliminated.
7, failure phenomenon: the image is normal, no sound.
Analysis and Maintenance: According to the analysis of fault phenomena, the cause of this fault is roughly sound processing, sound power amplifier damage or power loss, speaker open circuit or circuit disconnection, mute circuit control and so on.
First, try the AV input DVD audio signal and find that the speaker can produce a pleasing sound, indicating that this part of the circuit (including squelch) is normal. It is suspected that the root cause of the fault is a digital integrated high-frequency tuner with no audio signal output.
Observe the no-waveform change of the (12)-pin (AUDIO) of the high-frequency tuner with an oscilloscope, and only see the X axis of the oscilloscope screen on the horizontal line. Follow the route of foot (12) and find that there is no audio signal waveform on the audio output pin of the TDA9865. After finding a new replacement, sounds returned to normal.
8, the phenomenon of failure: when watching TV, the machine suddenly stop failure, key scan and remote control buttons do not work.
Analysis and maintenance: According to the principle of LCD LCD TV, the machine is in normal working condition, it is forbidden to connect the signal line of the periphery, otherwise, the whole machine will automatically enter the state of self-protection.
Through the investigation of the users, the reason for this failure was that when watching TV, I wanted to watch a DVD disc. I thought this was not a malfunction and informed the user that in the future, the machine would be powered off after five to ten minutes. , and then boot, wait for the MCU reset to reset, you can return to normal.
9. Symptoms: The entire screen appears a flower screen with normal sound.
Analysis and Maintenance: According to the working principle of the LCD display, it can be seen that such failures are caused by abnormalities such as poor contact and falling off of the backlight driver (inverter) circuit and the LCD panel driver (excitation) circuit connection lead.
After careful inspection, there was no obvious contact failure between the backlight driver and the LCD panel driver (excitation) circuit. Try 98% anhydrous alcohol cleaning, wait 10 minutes, power on, Huaping phenomenon disappears on its own. Since then, there has been a poor connection at the connection.
10, failure phenomenon: LCD screen appears the entire whiteboard screen, occasional Huaping phenomenon.
Analysis and Maintenance: This type of failure may be caused by poor connection between the backlight driver and the LCD screen driver circuit.
Try 98% anhydrous alcohol to clean the connection, the fault remains the same, with a magnifying glass observation found that some leads have been off, because the lead is made of silicon conductive rubber to suppress a one-time molding, it can not be repaired.
After replacing it with an imported M150X3 LCD screen, the image returns to normal.
11, the phenomenon of failure: the image, audio, color are normal, but the LCD screen in the lower right corner appears no light.
Analysis and maintenance: According to the LCD screen display principle is known; the root cause of partial lack of light is the backlight aging or LCD screen is affected by external forces, due to impact damage. Analyze the fault and assume that the LCD screen has been damaged.
First remove the boot and use an oscilloscope to observe the voltage across the backlight at approximately 2030Vp-p (with a 100:1 probe). The uniformity of light emission is normal. Power off and shut down. Observe the slight crack marks in the lower right corner of the LCD screen. After observing with a 10x magnifier, it was confirmed that the screen has been damaged by external force. After changing screens, troubleshoot.
12, failure phenomenon: black and white images are normal, but no color.
Analysis and Maintenance: According to the principle of no-color failure, the color decoding circuit is abnormal or damaged.
First, observe the 24,576MHz oscillator waveform between pins 7 and 7 of the U800 using an oscilloscope. Normally, the power supply is considered normal. After careful inspection of the discrete components, no abnormality is found. Replace it with a new SAA7114H. Power on, color return to normal.
When replacing the components on the digital signal circuit board, electric hot air gun welding or PTC non-inductive electric ferrochrome should be used. The printing plate is designed for four-layer, six-layer and eight-layer high-speed boards. Care must be taken to avoid overhaul. Damage to the circuit due to static electricity, resulting in the whole machine can not be repaired or scrapped.
What are the common types of faults in Konka LCD TVs? How can they be repaired? How can faults be quickly diagnosed? Today, the author shared with you a few more typical Konka TV fault repair cases, including specific operating procedures, and interested friends should not miss it.