A few days ago, I repaired a Konka LED26F3300CE LCD TV. The fault is that the startup picture is normal and the remote keying is normal. About 10 minutes or so, the image disappeared, the screen was full of vertical color bars, there were noise spots, the screams in the speakers, and the keyed remote control failed. The preliminary judgment is that the power supply of the main chip suddenly becomes lower.
Disassemble the machine to observe the machine as a 3-in-1 motherboard, version 35017209. After analysis, the machine's switching power supply outputs two sets of voltage. One set of 76V is used for the LED boost circuit, and the other set is 12V. The 12V is stepped down to 5V by N802, FR9888, and DC-DC modules, and the 5V is printed by N80 silkscreen W33J, N810 1117-25C, N808 1117-33C, LDO linear regulators respectively output 3.3V, 2.5V, 3.3V. 5V also through N801 silk screen HL20B, DC-DC module step-down output 1.22V core voltage VDDC. The above voltage is almost unchanged when the TV fails, indicating that the power supply of the main chip N501 should be normal!
After thinking about the crystal frequency drift of the main chip, there will be some strange faults, so replace the Z501 27M crystal and the matching capacitors at both ends of the crystal. The fault reappeared after 10 minutes of test. It is suspected that the pin of the main chip N501 MT8227AAKU has a solder joint causing this fault, and the pin of the main chip is observed with a magnifying glass and each pin of the main chip is swayed with a pointed dice. Did not find the main chip pin has a virtual soldering phenomenon!
Repairing this step is really a bit of a waste of water, and once again carefully observed the fault phenomenon, found that the fault phenomenon is very similar to the main chip and DDR clock line contact, but the machine does not have external DDR? Is the main chip N501 built-in DDR, and the grounding of the DDR block is grounded through the bottom heat sink of the main chip? ! Immediately turn over the motherboard 35017209, brush a little solder paste on the bottom of the main chip N501, use a soldering iron to plate a little tin on the copper foil grounded at the bottom of the main chip, and move back and forth to make the bottom of the main chip evenly heated, so that the tin passes through the copper foil. A portion of the via flow is applied to the heat sink at the bottom of the main chip. After the main chip was cooled, the test machine failed for 10 minutes, and the test machine failed for one day. The three daytime faults of the test machine still did not appear! It is determined that the fault has been eliminated. Thanks for watching!
The system to realize the automation of liquid level control is composed of hardware and software. The hardware mainly includes PLC touch screen and related CPU, memory, output and input, power supply and other modules. The on-site measurement includes all kinds of sensors and switches suitable for different on-site conditions. In addition, it also includes audible and visual alarm lights, control buttons and other related equipment. By configuring PLC liquid level display alarm instrument, it can realize the display of industrial field liquid level measurement, the alarm of high and low liquid level, as well as the opening and closing of pumps, valves and other equipment. It can realize unattended automatic workflow, greatly improve the production efficiency, save human cost, and bring about the increase of enterprise benefits, Lay the foundation for enterprises to take the lead in the severe competition in the future. Therefore, in the current situation, whether it is a new project or a transformation project, it is suggested that if conditions permit, starting PLC equipment is the priority.
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