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PSU or inverter problem?

Hello, May I ask for your help please? I read a posting from you regarding an Olivea LCD TV and you suggested it's likely to be a capacitor problem etc. My TV is a Haier but has the same symptoms of a blue screen for 1 second. Having measured the transformer primaries I'm seeing 900 ohms, so have ruled them and dry joints out because the screen is full blue, no missing bits etc. The PSU is giving 25.3v on the 24v line either with or without the inverter connected. Otherwise the PSU seems fine. I can't see any bulging capacitors either, so this has me stumped! Thanks for your time, Ian - UK

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  • iansmusical
    iansmusical Dec 23, 2008

    Hello, Thanks for getting back to me. No the set remains powered on just the backlight that isn't working. I do understand these Darfon V144 boards are terrible! Admittedly there are about 11 caps on the inverter board but I don't have an ESR meter. However, they'd be cheap to replace! Is it worth unsoldering all the transformers and checking their resistance out of the circuit? What about powering the inverter from a separate PSU to rule out the sets PSU? Incidentally there's 0.5v on the FB pin of the OZ960 on the inverter board and 0v on the OVP pin. Thank you for your continued help. Ian - UK

  • iansmusical
    iansmusical Dec 24, 2008

    Hello, Do you happen to know if a Darfon 4H.V1448.291/B1 inverter will work as a replacement? They don't have the single wire connector, which comes from the other end of the CCFL tubes, is that a problem? I don't have the replacement caps at the moment but I did try a 100uF cap (same as original) in parallel with each cap in case they'd gone open but it made no difference. The fuses on the board are also ok, which I happened to notice today too! Thanks again for your help and have a great Christmas :-) Ian - UK

  • Sonny Berry
    Sonny Berry May 11, 2010

    does the set power down after the blue screen or continue on to operating? If it powers down I would suspect bad caps on the inverter, often they wont show any sign of bulging, A ESR meter will quickly pinpoint a bad cap in circuit if you have access to one, Which wuld be alot cheaper than replacing panels that may or may not need replacing.

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I would recomend replacing the 11 caps on the inverter as 90% of the time its failed capacitors on the inverter. If you shine a bright light into the screen can you see the pic? Thats usually one of the first things I do when I suspect bad caps on the inverter.

Posted on Dec 23, 2008

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Olivea tv rc-lte remote


Do you mean that the source button on the TV itself does not switch to the input of the TV that you are connected to?

Apr 22, 2013 | Olevia LT32HVM 32 in. LCD Television

Tip

How to test an LCD TV or monitor PSU and inverter


Hi.

Before proceeding I assume you have technical training along with the multimeter. A full testing must be done with power on, and for safety reason must not be done by an untrained user.

The tip contains only general indications. The reader is supposed to have the training to apply in practice the testing method below.

If there is no power at all, then the responsible is almost always the PSU.

When there is no power, test AC in to PSU. If there is no AC in (read volts, or read ohms on power cable), that means that the power cord must be replaced.

If there is AC in, then test the PSU section near to AC input. You always find a resistor or a fuse in there . Check if it has blown.
After that you test the rest of PSU component. If there is no power at all , and problem is not power cord, it is often possible to spot at a glance a leaky or bulged capacitor.

If there is power, but the monitor stays in standby, then te PSU is forced to low voltage only by controller board. This happens when a fault had been detected.

In this case testing the PSU becomes more complicate. The technician must locate the control lines from controller board. This control lines operate at lower PSU voltage (often +5V), and turn on higher voltages on PSU board.

The inverter may use for example a +20V line from PSU. The +20V line is turned on by the controller board, closing a +5V control line to PSU. When PSU is in standby mode, the technician testing the PSU must bridge the +5V line with the PSU low +5V circuit, and test if the +20V line to the inverter gets turned on.

As explained this kind of test must not be done by the unexperienced user, as the chance to waste the unit beyond repair is high, and there are also many safety concerns.

After testing the PSU, next part to test will be the inverter board.

The inverter is tested reading DC voltage in from controller board, and AC out to back light system.
The inverter is an high voltage board, remember, safety first when testing AC circuit.

If the inverter has no DC from controller, then test PSU, if PSU is OK, and inverter has still no DC in when PSU line to inverter is on, then replace controller board.
If the inverter has DC in, and no AC out, then replace the inverter.
If the inverter has DC in and AC out when higher DC voltage to inverter is turned on, then test at component level the main controller board, and if present test LCD controller.

Regards.

on Mar 03, 2010 | Flat Panel Televisions

1 Answer

Got sound but no picture on my tv.


Hi.

First check if you have on screen menu and if the problem is still there if you change input source and cables.

If TV has no backlight on all inputs, then it is either inverter not supplying power to the backlight system, or the LCD panel itself. The inverter or the parts connected to the inverter are common cause for the problem. The LCD panel is not a common fault. When problem is the panel the TV is not worth repairing.

When there is an inverter problem the fault is not necessarily the inverter. The technician needs to test the parts to find out what part is responsible. Testing is done tracking voltage from PSU to inverter. Voltage to inverter is usually supplied by the higher VDC line from PSU. Here broad description of how to test the three parts: Before proceeding...

Here replacement parts for most flat panel TV models:ShopJimmy.

See also:
PartStore

Regards.

Ginko.

Sep 20, 2011 | Sanyo DP32746 32 in. LCD Television

1 Answer

Philips 32pf9641d/10 fault works well for 90 mins then goes black still images on screen but no backlight ? power supply or inverters? if inverters can they be repaired or replacement only,


Hi.

As you said when there is no backlight the problem is either inverter or power board. In some case the main controller board may be responsible.
You need to test the parts to find out what part is responsible. Testing is done tracking voltage from PSU to inverter. Voltage to inverter is usually supplied by the higher VDC line from PSU. Here broad description of how to test the three parts: Before proceeding...
The TV can be repaired at component level or replacing boards, depending on your skills and experience. If you want to repair at component level, after diagnosing the faulty board you test components and circuits individually. In that case to test inverter in full you will need an oscilloscope to read the phase of inverter AC section (oscillators or IC must be tested).

Note: If Inverter has voltage out to CCF lamps, then the parts mentioned above are OK, in that case you have a faulty LCD panel. The TV is usually not worth repair as the LCD panel is expensive. LCD panel faults are not common.

Here replacement parts for most flat panel TV models:ShopJimmy.

See also:
PartStore

Regards.

Ginko.

Sep 20, 2011 | Flat Panel Televisions

1 Answer

I have a Samsung LE32R88BD TV 4 yrs old that when switched on now shows an image on the screen for about 1/2 second and then goes black. The audio of the channel continues.


Hi.

Check if there is on screen display (there should be none) and make sure that the problem occur with all inputs.

The problem is either defective PSU or defective inverter board. A bad main controller board or LCD panel can give the same problem but it is not common. Testing is done tracking voltage from PSU to inverter and LCD panel.

Here basic troubleshooting.

If the problem is not the connection, then it is usually the inverter not getting powered. In that case PSU, main controller board and inverter must be tested. Here general explanation of testing involved: How to test an LCD TV or monitor PSU and inverter.

Regards.

Ginko

Aug 28, 2011 | Flat Panel Televisions

1 Answer

Screen is like a strobe


Hi.

Problem is inverter, backlight or PSU. The backlight lamps that illuminate the LCD display are flashing. This creates the "kind of strobe" effect that you see. There are several possible causes for the problem.

The lamps themselves are defective. The lamps do not fire up completely and keep flashing. The lamps are not sold alone but they are part of the LCD display. If the lamps are gone the TV is not worth repairing.

The inverter is the high voltage board that supplies the backlight lamps. If the inverter is defective it can still be replaced. Testing is done reading DC in, checking high voltage out, and using an oscillator to test the phase of the AC out signal generated by the inverter oscillator section.

PSU or main controllers may be defective. This will less common in case of flashing back-light. Test this if the inverter is OK and if the problem is DC voltage input to inverter.

Here parts: 42LA30H - ShopJimmy

Regards.

Ginko

Aug 11, 2011 | Proscan 42LA30H 42 in. LCD Television

2 Answers

My protron tv pltv-32c has no picture but has sound, if you change channels the picture will flash on for about 1 second


Hi.

If there is sound but no picture, screen is completely dark and the picture is occasionally flashing, then the fault is likely a faulty inverter. In some case a faulty controller board or a defective PSU can cause the same problem.

I summarized the problem here:My LCD TV has sound but no picture.

I posted general procedure to test inverter, PSU and controller board on LCD here : How to test an LCD TV or monitor PSU and inverter.

If screen is not dark, but has blacklight or noise things are different. In that case check connection cables first. Parts that may be defective are main controller board, terminal circuit and tuner board.

Protron parts are available using the link below. Ensure that parts are compatible with your model before purchasing.

ShopJimmy - Protron Parts.

Regards.

May 15, 2010 | Flat Panel Televisions

1 Answer

Has sound and no picture


Hi.
Ensure you have alredy disconnected power and left TV not connected for at least one hour.
If it is a rear projection model it can be a problem with optical group, video or ballast board. In this TV however this problem is not common, usually the TV goes in standby.
On LCD the problem is often caused by a faulty inverter, in some case bad controller board or PSU with no volt on inverter line to controller board (higher DC voltage). In some LCD inverter is on same board with PSU. Most common is inverter.
Read more on LCD here:My LCD TV has sound but no picture.

Dec 16, 2009 | Flat Panel Televisions

1 Answer

Haier Inverter board PSU/CCFL question...


change the lamps unit will work fine.
regards,
daniel

Jan 12, 2009 | Flat Panel Televisions

1 Answer

Either PSU or Darfon V144 inverter backlight problem?


Hi, Please measure all windings again and see if there is one lower than 900ohm. All CCFL might seem working but only for one second before the protection circuit cuts in. By the way, there is something that I would like to know, what is the type number of your remote control?

Dec 22, 2008 | Flat Panel Televisions

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