Monday, January 3, 2011

【 Weak current College 】 color on repeat firing line pipe of a discussion 】



In the maintenance of trouble-free color TV III, line pipes puncture damage is one of the most common phenomenon, since the line pipe damage caused by the reasons are many and complex, maintenance personnel during the repair process often encounter some difficulties. This article combines the maintenance work on the actual rows of tubes from causing damage to the most common reason that voltage breakdown, current breakdown, loss of a three-pronged approach, such as breakdown of line pipe burn and maintenance methods.

A, voltage breakdown

General TV line pipe pressure value more than the 1500V Typ, color TV with in-line tube on line c very backward pulse voltage to about when row 1000Vp-p backward pulse voltage becomes elevated line pipe is easy breakdown damaged. The line backward Pulse rise of common causes are: (1) line power supply voltage, line backward pulse voltage is the power supply voltage of 8 ~ 10 times as long as the lines of rising scores of volt power supply, backward pulse will exceed 1500Vp-p and breakdown line pipe; (2) rows backward capacitor failure or reduced its capacity. Backward capacitance is an important decision backward component of the time, when its failure or capacity reduction, backward time becomes too short, causes the rows backward pulse amplitude increased the line pipe breakdown; (3) row frequency too high. If row frequency too high, the time is shortened backward, backward pulse rising to line pipe breakdown. Line tube voltage breakdown of features, post as "important", or high pressure nozzle when powered on at the exception of acoustic measurement of line pipe at the c, e very resistance almost 0 Ω.

Example 1] KONKA T2106-no TV, no 3, "Squeak" sound. Check that the line pipe c, e very breakdown. After the demolition of Downer 105V output and 60W light bulb with side access as false load, power-on test 105V Terminal voltage normally. Swap the new row after restore original circuit system. Observationtwo hours with no exception, but returned to users in three days and three no failure and return, measuring line pipe Q402 and breakdown. After analysis, the moment breakdown line pipe, is likely to switch the power supply voltage is too high. Once again, remove the access lamp 60W Downer, measuring the bulb voltage, found on the moment of its voltage 176V, and then reduced to normal 105V, keep right on observation, 105V voltage without overshoot. From this analysis, the focus should be questioning STR-S6309 and its surrounding components. Discover capacitance C912 (23 μ F/50 V) appearance of a heat-curing, measuring its capacity is only 0.6 μ F. Due to the loss of capacity, C912 IC902, Q901, IC901 working voltage, output voltage of power supply caused by rising burn line pipe.

[2] a Venus C514 TV appear three trouble-free. According to the user, this machine a few days ago has replaced the three non-fault line pipe. I'll line pipe D1453 changed after power on, figure sound fine, but when you have temporary post "count". Cooling and power-on test B1 voltage is then reduced to 125V, 105V and branch supported sound disappear, with an emphasis on testing the circuit of electrolytic capacitors, found C714 (47 45 μ F/V) capacity very unstable after troubleshooting, replacement.

[Example 3] Sony KV-2965MTJ TV panel led flashing, Matt silent. Check the switching power supply's output voltage of + 5V, + 14V, + 22V, + 135V are OK, check row scan circuit, measuring line variable ④ feet + 135V input voltage 0V, + power supply branch circuit breaker 135V. check damage, while at the lines R340 tube 2SC4927 damage. Replace these two components, the commissioning of 2 hours is no exception. Paying users a month again, drill down, switching power supply section and row, field power parts are not unusual, whether power module IC601 (STR-S5741) soft fault exists. When the plastic plate removed when you are ready to replace the power supply module, only nine pin STR-S5741 solder joints are tiny cracks, the solder joint heavy welded over R340, then replaced, after commissioning Q802, troubleshooting.

Second, current breakdown

When the line pipe work power consumption exceeds the maximum allowed value. Line pipe will be severe fever, and caused the breakdown of line pipe power increase of common causes are: (1) line is overloaded. If the line output transformers and motor, row deflection coil turn to turn short-circuit, etc. (2) inadequate stimulation rows. When a line drive transformer PCB solder pin and any cracks are formed a contact resistance in series in a line drive transformer and circuit board line pulse between. the resistance must be hampered, line output tube b be incentive enough, pulse amplitude caused line pipe from the globe to saturated for longer, line pipe power increase and severe heating breakdown. Line tube current breakdown of the characters are: a few minutes after the line pipe temperature rise higher, measuring line pipe c, e very General of resistance values for dozens of ohm to several dozen stem ohm.

【 Cases 4 】 TCL, 9329Z award-winning line of pipe, splash damage is three. Check that the line pipe Q402 c, e very breakdown, unplug CN904, C926 ends a 60W light bulb in parallel as false load, measuring + B voltage 1.40V and stability. Power on the phenomenon of the moment without overshoot, check row backward capacitance C430, C431, C414 are OK, check row-level, not promoted, replace the line pipe on the machine, and breakdown, and see both the neck of the tube, I discovered that sparks is the deflection coil turn to turn short-circuit and cause this failure. Third, before hitting the dental loss

A loss caused by failure due to voltage, current, basically unchanged, and tend to be normal, often difficult to make accurate judgments. common fault reason mainly been loss are: line promotion, row frequency is low, the output level of decoupling capacitor and line drive decoupling capacitor metamorphic grade. The breakdown for a loss, the author encountered CHANGHONG C2588 TV power on three no, the Player checks, power fuses, line output tube breakdown, replace the line output and power supply fuses to prevent after the power supply output voltage breakdown line pipe, disconnect the line output-level power supply resistance R444 (see Figure 1) + B (115V) output termination 300Q resistance as false load test machine+ B voltage 115V normal and stable within half an hour. Removed bogus load, in the end-line ammeter R444 and try again. acousto-optic figure appears and is normal, as the image brightness of dark out, line-level output current in the 420mA ~ 550mA basic normal between changes. Think TV repaired, to users, but the next day the user tell the TV again. This time I passed the safety measures, power-on test machine, everything is normal, but the touch line pipe temperature rise significantly higher, due to voltage, current, judgment is a loss to line pipe damage, its cause has row frequency is low, the row is not enough native image promotion line synchronization. And row frequency low fault occurred in the use of crystal oscillator circuit for line scan, while the machine adopts TA7698 no oscillator, judge line drive. But the line drive pipe, line drive transformer replacement fault persists, then carefully observe the circuit board components. Discovery line level decoupling capacitor boost C486 close to the power of resistance, the skin is atrophic, remove the detected no capacity to replace C48C tongue, fault completely ruled out.

Because the line advance level decoupling capacitor failure: decoupling lenclos cause line drive level produces the self-excited, since stress wave series to promote the signal line, and useful line drive signal but not enough to enlarge the output pipe loss increase in temperature is too high, the pressure drop and breakdown.

[Example 5] West Lake C6405 TV watching without suddenly appears. According to the user, after a failure, are replacing the line output after the TV back to normal, but watching an hour after the failure. In order not to damage output tube. The author has adopted the following maintenance steps: first disconnect the line output-level power supply circuits, switching power supply + B (125V) output access 300 Ω/50 W of wire-wound resistors forgery detection shunt voltmeter load + B voltage (see Figure 2). Power more than two hours, + B voltage normal and stable and that eliminates switching power supply output voltage rise breakdown line output tube. And then remove the dummy load, line output-level power supply circuit-a fuse and ammeter 0.7A so that line current increases protection output tube. Replacement may fail after traveling backward capacitor power on the machine. Sound and light map properly, + B voltage stability, line output pipe temperature clearly on the high side, in watch 40 minutes later suddenly is three. Power-off check. Line output tube breakdown, in-line fuse fuse, but in the event of line output tube breakdown, did not find the voltmeter and ammeter any abnormal reaction, description line output tube is instantaneously breakdown, and fuse is in line pipe breakdown after the fuse, then only one possible, is a loss to line pipe damage. Back to C2852 deformation, replacement line pipe temperature drops, the machine is composed by L810, C852 rows output decoupling circuit, filter out rows output transformers produce high-frequency interference pulses when C852 failure, high-frequency interference pulses will flee into other function circuit, especially channeling join oscillation and the line drive circuit, causing the line scan circuit caused the self-excited, line output pipe loss increase component temperature rise, the last strike line output tube.

Besides conventional TV line output decoupling circuit most RC coupling, General resistance of resistance is small, when the capacitor failure due to a power supply decoupling filter capacitor charge. damage does not result in the output pipe line, this machine uses the decoupling inductor capacitor, increased decoupling effect, but when the capacitor failure due to the high-frequency signal inductance on blocked, allowing high-frequency signal through the decoupling filter circuit, go directly to line drive-level and other functional circuit, causing the failure.

Also of note is the high-voltage spark, this can easily cause damage to the pipe line. As high pressure CAP in CRT does not cause high voltage spark securely attached, and line output transformer internal or external brand impact.

Summary: to sum up, no matter what kind of TV repair first to ascertain the cause of the causes of damage to the pipe line, to distinguish the fault lies in the power supply parts or in the power of the load area. Free simple approach will disengage and line load line power supply connected to false if the load voltage measurement, is there any overshoot. As normal, fault on the part of the load; on the other hand is the switching power supply has failed. Then, check row load sites initially, because this site is the high voltage, high calorific value, easily lead solder joints loose soldered failure. In with the naked eye cannot see that a faulty premise, you can post check voltage or current, and c in line pipe into the extreme series 500mA fuse case line pipe caused breakdown, again the second time damage such as meter reading values in the normal range, it is necessary to consider decoding circuits generated row frequency signal frequency is normal (available frequency table to check), and the row frequency signal into line load parts of the component is working properly.


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