LG 42lb5d - No Sound - No Display - Backlight is OK

[JBlazeRSP]

I'v searched and searched and can't find a solution. No visible bad caps. On one of the connectors the 19v pin measures 17.8v I don't know if that would cause this.

No display (or sound) of any kind other than the backlight glow. Anyone got any ideas?

Love this site. Fixed a few tv's already just by reading threads here.

Thank you very much.

[PlainBill]

Re: LG 42lb5d - No Sound - No Display - Backlight is OK

I've got a number of ideas.

1. There is a problem, probably with the main board.

2. The service manual may help.

3. Check the voltage regulators on the main board.

4. The next person who requests help with an obscure model of TV, but doesn't provide pictures will either be ignored, or will wish he had been ignored.

PlainBill

[JBlazeRSP]

Re: LG 42lb5d - No Sound - No Display - Backlight is OK

Here are some pics. In the middle vertical connector is the 19v that is reading 17.8. Also,, the green power light flashes 18 times then turns solid. That's when the back light comes on.

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[blazecin]

Re: LG 42lb5d - No Sound - No Display - Backlight is OK

Did you ever do anything with this lg i know its been years but i have the same thing going on now.

[tvnewbie2]

Re: LG 42lb5d - No Sound - No Display - Backlight is OK

I have a problem with my LG not wanting to load past the LG life's good first boot screen.

[Doc_Falworth]

Re: LG 42lb5d - No Sound - No Display - Backlight is OK

For anyone else landing here looking for free directions:

I own this very same model television 42LB5D or specifically 42LB5DF

The most common problem I have experienced as many others have is that the switching power supply fails on the low side. Power supply circuit board is pictured in post #3 as a tan board. In the picture the low side is the upper right corner of the tan color board.

The first part of troubleshooting is to measure output voltage(s) from the power supply. The power supply no matter what model is generally marked with output voltage or at minimum a three to four letter description. For example standby would be STBY power that should in most cases be 3.3V to 5.0V depending on model of television. As a rule most pin connectors, sockets are marked.

Some failed capacitors are easy to identify by bulged top, bulged bottom, or both. Some actually begin to weep or ooze their contents. Those are the easy ones to identify.

Capacitors that have good physical characteristics can still be dried up inside thusly rendering them as a complete short or complete open circuit.

There are (inexpensive) tools for testing capacitors while they are still mounted to the circuit board however the most reliable way to test any capacitor is to remove it from the circuit by unsoldering it or removing it from the board.

This same practice is true when testing diodes (look like resistors but have only one line).

Since both capacitors and diodes are very inexpensive and the most common failures it makes good sense to at least test them and replace the known bad components first. Worse case scenario is you wasted a couple hours and maybe five bucks worth of parts.

Lower than anticipated voltage such as OP indicating 17.8V and not the anticipated 19.0V is a sign of trouble. Over one volt plus or minus is a considerable difference from reference. A value like 18.2V would be on the very low side of 19.0V reference but may still seem to work fine. If you divide 17.8 by 19.0 you end up with a difference greater than 5% which is a lot. Think of difference as a tax. Lower is better, none is best!

The 42LB5D failing to boot beyond the LG splash screen is telling you it passed the power on self test but fails the component loading process. 9 times out of 10 it is because of under voltage which is a safety. Low voltage or open circuit should interrupt function if only to identify a problem or should completely shut down the system.

I replaced the power supply for my LG42LB5D for $25 used tested good from eBay. I kept the old one to troubleshoot later. Mine had a shorted transformer, 5 bad capacitors, and two shorted diodes. I believe this damage could have been prevented because I kept using the TV knowing full well there was something wrong with it. Had I taken it apart when it was first showing sings of problems, replacing the bad caps may have saved the other parts. The old power supply was not worth fixing for me so I scrapped it.