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Check all the solder terminals at the vertical output IC. Re-solder all of it by applying a little more solder to each solder terminals. If it do not help you, desolder out the vertical output IC, and check all the related components. Check and replace damaged one/s. If you wish to get some details; check the site linked here. Viewing it in "Mosaic" will make surf easy. Surf the site with patience. Pull up older posts. Surf the site with patience. http://electronicshelponline.blogspot.com/
Horizontal line on screen denotes the absensce of vertical sweep itself. Check the vertical output section circuit to LA7840. Check for any loose solder terminals. It will be best to measure the input voltage to that IC from the LOT secondary supply. Try by replace the IC. If these do not help you, measure the frequency from the main IC. It should be at 50Hz. If this frequency is not present, the main IC is faulty. If you wish to get some more details about the circuit, check this link. http://electronicshelponline.blogspot.com/ Pull
up older posts there, either by its left side bar, or see it in Timslide
option. Schematic diagrams, that show vertical IC LA7840 is given. You can compare it.
You can replace the LA7830 linear integrated circuit with any of the following parts:
Replacement part type / code
1508-07003A-00
ECG1773
IX0640
KA2131
NTE1773
SK9752
I've found the replacement parts in a specific website that allows you to find replacements for integrated circuits and semiconductors: http://www.icreplacements.com
Your TVs vertical output section has the fault. You just open your TV after disconnecting it from the AC mains wall socket, and locate the vertical output section. This section uses an Ic marked as part [IC 401] on the board and its number is LA7840. Just look for any loose soderings around its components legs, and the solderings at the IC legs, which has 7 of them. The IC stated above will be screwed onto a heatsink to radiate heat out of it when it works.
If all soldering point are fine, come towards the IC legs and measure the voltages at each leg. The voltages must be
pin 1= Ground
pin 2= 12.6
pin 3= 24.7
pin 4= 4.4
pin 5= 4.4
pin 6= 24v [vcc]
pin 7= 1.8
All voltages stated above are DC voltages with respect to ground. If any of this voltage is missing, find out the reason for that. If all of them are noted abnormal, IC may be defective, and replace it.
[vcc] stands for main input voltage to the IC.
If you need any more assistance, feel free to contact me through Fixya. Ok.
Possible that the vertical drive IC has failed . But make sure to test the voltage on the IC as if the voltage is not present on the IC thenthe saem problem can happen andit can be due to a failure of the fusible resistor from the LOT.
So check this before you replace the IC.
Usually if a problem of a monitor is the main IC itself, it is recommendable to buy a new one (since the price of the main IC is almost the same price as a new one itself. (depending on where do you reside) in our country, we consider buying a new one when the issue is the IC itself since here, the price of the IC is almost the same price if you buy a new one (about USD 100 for a new LCD monitor, while a main IC costs about 70 to 90 USD)
sounds like you might have an auto overvoltage shutdown circuit kicking in. The hivoltage goes to high and the monitoring circuit auto shuts down. More than likely trouble is in hivoltage circuitry. If you have a transformer that will allow you to bring up the set slowly without shutting down and you can look to see what's happening.
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