Question about TruTech PVS31170S1W 17 in. LCD Television

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Picture fades to black 20 seconds after turning tv on but sound if fine -picture filament or tube finshed/ thank you for any reply

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  • TruTech Master
  • 5,103 Answers

On an LCD TV, the usual problem is the backlight or the inverter. In this case it's more likely to be the backlight (it slowly fails or turns the images pink/red).

For an out-of-warranty TV, open up the back of the TV and remove the shielding. Look for any scorch marks or bulging or damaged capacitors. (Sometimes other parts will fail on this part but these can be spotted easily. Capacitors look like cylinders on a tripod.)

If you borrow (or have a) high-end multimeter (able to measure high frequencies - 50 kHz) or an oscilloscope, hold the multimeter probes a fraction of an inch apart about an inch above the board and power up the TV. If you see a 1 or an actual value, you have a good inverter. If you see a reading near 0, the board is bad or the multimeter can't resolve the frequency.

In either case, you can buy a replacement inverter for $50-150 and just do a simple swap. Disconnect all of the wires (connections are similar to molex and ribbon cables in a computer) and remove board (a few screws usually). Connect the cables to the new inverter. (If you google backlight inverter replacement, you'll find videos and text descriptions.) Note the part number on the board, including the Rev number, and order the exact one (shopjimmy.com or lcdparts.net are good starting points). Universal inverters do exist but can result in reversed controls (up to lower the brightness). Replacing individual parts on the board is cheaper but more prone to not tracking down all of the bad parts.

If the inverter is good, then it's probably backlights themselves (several in most TVs). These are sandwiched on the perimeter of the TV (usually under some tape that holds the lamp, reflector and other parts together. You need to order by length and width and get ones for your TV size. Remove the tape, and separate the reflector (make a note of how things are put together) then you have to Dremel (or use another rotary tool) to remove the plastic to get the backlight out. (They are often molded into the frame.) Then put in the new backlight and reassemble everything.

With a good spare backlight, you can test an inverter for condition (plug together and turn on the tv while the box is open). Similarly a good inverter can test the backlight.

I hope this helps.

Cindy Wells
(with a bad backlight, you'll usually see a very dim image if you look at the TV from an inch from the screen. Block the room light from overwhelming this image (sometimes a carefully positioned flashlight will help you see something). If the inverter or video board is bad, you will see nothing.)

Posted on Jul 08, 2010

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Hello,

If the picture faded away on the order of 10-20 seconds (and if it comes back, also comes up to full brightness in same time frame - possibly with the persuasion of some careful whacking) AND with NO other significant changes such as size, focus, etc., then take a look in the back of the tube for the filament to be lit - the orange glow near the CRT socket. If there is none, then you probably have a bad solder connection on the circuit board on the neck of the CRT. Look for fine cracks around pins on that board. Try prodding it with an insulating stick to see if the picture comes back. Resolder if necessary. Dirty or corroded CRT pins/socket contacts can also do this - remove, inspect, clean, and replace the neck board. It is probably not a bad CRT as the filaments are usually wired in parallel and all would not likely go bad at the same time.

However, if only a single color fades in and out, then a bad connection inside the CRT is a distinct possibility - look for only one of the filament's glow to be coming and going. This is probably not worth fixing.

If the picture faded away with other symptoms, then there is probably a fault in the video amplifier/output one of its power supplies - still probably a loose connection if you are able to get it back by whacking.
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Check the CRT ground wiring. I saw this on a computer monitor after I forgot to reconnect the wire from the ground line around the picture tube. It would start normally and fade out over a period of five-fifteen seconds.

Caution: pull the plug and wait several minutes, then check for voltage between the bare wires around the outside of the picture tube and chassis ground before you put you touch anything. If you get voltage, this is definitely the problem, and I've just saved you from a nasty shock (could be almost as high as 2nd anode voltage). If you don't get voltage, inspect at will.

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1 Answer

Picture slowly fades,then comes back and repeats


Stacy,

Sounds to me like there is bad solder somewhere on the filament supply circuit. Do you know what a cold solder joint looks like? It is a solder joint that is not making a good mechanical or electrical connection. When you lose that connection the filament inside the tube slowly stops heating the electron guns and the picture will fade away. When the connection comes back the video will come back.

Might be worth it to take the back off and check out the little board that is connected to the end of the tube. The problem is either there or on the power supply.

Shouldn't be a problem for a repair tech. I would not spend very much money though.

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1 Answer

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You can reduce the g2 for the blue tube
open the front grill and open the 4 screws hold the resister block
to have acess to the register block.
Then there should be the black box have 6 knobs
the one call for Blue g2 not the focus block.
Adjust it counterclockwise a little bit
and try turn on TV again



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1 Answer

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Try to finde lose connection/ cold solder joint at board attached at end of picture tube. It seems heater/ filament voltage not being supplied to picture tube after a while and picture goes to black.

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1 Answer

Sony kv32s42 trinitron color tv blinking


sounds like a bad picture tube. Picture and bright settings cranked up for a good pic? Test/rejuv with a crt tester and/or look at the Ik signal on the crt board. A good tube has 3 small pulses during blanking. The crt cathodes are checked with these pulses, pulses too low and the jungle IC will blank the drive. If the picture fades in and out I would check the filament ckt but that doesn't support the "blinks"

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1 Answer

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The only thing I can think of that would make the picture fade to black is a loose solder joint on the filament supply. Each of the 3 picture tubes has a filament and if the 6.3 volt supply to those filaments is suddenly lost, the picture fades to black as the filaments cool down. An experienced tech can find and correct this for you quite easily.

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Isolate filament voltage from CRT,i.e. unplug Crt socket from pix tube.Measure filament voltage on CRT PCB.If present,suspect bad pix tube.If missing,solder any/all connects in filament circuit,meaning CRT board first then main PCB.

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1 Answer

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Bad technicians always say picture tube problem when the TV has black screen with sound. This a false statement and in some cases techniciacns use this to scare the owner or the charge a hefty amount. The truth is that picture tube outlast most component in the TV. If it will fail, it is gradual like the colors will fade or one or several color will be missing. This condition is the degration of the filament in the gun (CRT tv has three -Red, green , blue) I started to repair TV in the early 80's and only in one occasion that the Tube fail and it is a crack in the neck. For black screen with sound, the most common cause is the HV supply problem / Horizontal section. This can be caused by many things, like flyback transformer failure, horizontal outout transistor, horizontal drive, etc. For the cost-depends on where you are, in some countries labor is dirt cheap, in other ountries the parts are expensive.

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