RCA L40FHD41 LCD was dead, replaced all caps on PB, now has no audio

[2hamburgers]

So here I am, a proud noob making his first circuit board repair. I got this RCA from a pawn shop, they claimed it worked fine until it just stopped turning on one day. When i took it apart, i noticed 2 busted caps and 2 more bulgers on the power board. I replaced all caps regardless of how they looked. How proud i was to bring it back to life, but then I realized the audio would not work.

I was wondering if anyone else experienced this before? Lets give the pawn shop the benefit of the doubt and say they were honest. I cannot get ANY audio output(built in speakers or otherwise) from ANY input source. I know my devices work and i tried adjusting tv settings and resets to no avail. I know the general drill for visual inspection and its all ok. I have even tested all the SMD resistors (main board), I cannot find a problem. Anyone know what i might have done or anyone deal with something like this before?

[tom66]

Re: RCA L40FHD41 LCD was dead, replaced all caps on PB, now has no audio

Check the headphone output. If that works, focus your attention on the audio amplifier section and power supply for it. Also, what capacitors did you use? General purpose capacitors that most retail stores sell are not usable in LCD TVs.

[selldoor]

Re: RCA L40FHD41 LCD was dead, replaced all caps on PB, now has no audio

Do you have a remote for it? Longshot but check the mute button is not stuck.

[budm]

Re: RCA L40FHD41 LCD was dead, replaced all caps on PB, now has no audio

Yes, look at the user audio setup menu to see if the Internal speakers are set to OFF.
Also check the RCA audio line out to see if the sound is there, hook it up to the powered PC speaker system.

[cadiman]

Re: RCA L40FHD41 LCD was dead, replaced all caps on PB, now has no audio

I have picked up a few tvs and once repaired they had no audio.

The speakers were not set to off but as noted above the headphones were set to "on"
and that turned off the speakers.

On some types of tvs you need the remote to change the feature.

[2hamburgers]

Re: RCA L40FHD41 LCD was dead, replaced all caps on PB, now has no audio

Hey guys, excuse me for not getting back to you promptly. I had to leave town on business. I got around to following your instructions:

tom66: Checked headphone output: it works but barely, had to turn the volume up to 80% minimum to hear, both left and right worked. What kind of caps?: a mixture of Rubycon LD, Chang, Nichicon PJ(M), and Ltec?/Htec? PET. Bought them off ebay. I replaced them all regardless and used the Nichicon for the busted 1000uf16v caps on my board.

selldoor: Unfortunately your idea I would have never thought of did not work. The TV confirmed it with a crossed out speaker pop-up.

budm: The device is correctly set up on the menus. Powered speakers do not work when connected to the audio out. When its plugged into the headphone jack it works at a lower volume level than I would expect as I raised the volume on the tv, it also buzzed badly.

[2hamburgers]

Re: RCA L40FHD41 LCD was dead, replaced all caps on PB, now has no audio

I have picked up a few tvs and once repaired they had no audio.

The speakers were not set to off but as noted above the headphones were set to "on"
and that turned off the speakers.

On some types of tvs you need the remote to change the feature.

So your saying that some factory remotes give you the option to turn your headphone jack on and off? I have a universal remote and tried the mute feature and got a confirmation symbol, but no change. Im leaning towards a board malfunction after talking to these guys. It is nice to see that others have experienced the same phenomenon though.

[tom66]

Re: RCA L40FHD41 LCD was dead, replaced all caps on PB, now has no audio

tom66: Checked headphone output: it works but barely, had to turn the volume up to 80% minimum to hear, both left and right worked. What kind of caps?: a mixture of Rubycon LD, Chang, Nichicon PJ(M), and Ltec?/Htec? PET. Bought them off ebay. I replaced them all regardless and used the Nichicon for the busted 1000uf16v caps on my board.

Rubycon LD -- I have never heard of that Rubycon series? Are you certain? Chang and Ltec are not suitable either. The Nichicon is the only one fit for purpose in an SMPS.

[2hamburgers]

Re: RCA L40FHD41 LCD was dead, replaced all caps on PB, now has no audio

Excuse me, the Rubycons are YXF. So can those Chang or Ltec caps somehow be the cause of my problem?

[tom66]

Re: RCA L40FHD41 LCD was dead, replaced all caps on PB, now has no audio

They can be. They are generally abysmal capacitors. Rubycon YXF is fine.

[2hamburgers]

Re: RCA L40FHD41 LCD was dead, replaced all caps on PB, now has no audio

Well tom66, i still had the caps i replaced from the power board, and ironically they were all Chang, so if anything, its the way it was or better. Anymore suggestions anyone, i dont mind buying a replacement main board but i at least want to try to fix what i have......

[budm]

Re: RCA L40FHD41 LCD was dead, replaced all caps on PB, now has no audio

"budm: The device is correctly set up on the menus. Powered speakers do not work when connected to the audio out. When its plugged into the headphone jack it works at a lower volume level than I would expect as I raised the volume on the tv, it also buzzed badly."
Getting nothing at the Audio line out (Red and White RCA jacks) does not make sense since the audio line out (fixed output level, some TV will have it tapped off after the Voulume circuit to provided Variable audio level outputs) is tapped from the audio preamp section after the sound processor, that signal line is then fed the electronics Volume and Tone control circuits, the outputs of that section are then fed into the power amplifier sections for driving the speakers, in some TV that signals may be splitted off to feed the headphone amplifiers for driving the headphone only.But most of the time the headphone jack is connected to the power amp speaker outputs, when the phone plug is inserted into the switched jack, the signals are then routed to the Headphone jack instead of the speakers.

[2hamburgers]

Re: RCA L40FHD41 LCD was dead, replaced all caps on PB, now has no audio

budm, i did not follow your instruction exactly, i tested the audio out that uses the same jack as the headphone jack, I have to get some speakers to check the red and white outputs, i will let you know what i find after testing again correctly.

[budm]

Re: RCA L40FHD41 LCD was dead, replaced all caps on PB, now has no audio

OK, that is why. The audio out at the RCA jacks are less than 1V and it is made for driving high impedance load, so you will need to use powered speakers.
We are trying to find out if the problem is in the preamp section or in the poweramp section.

[cadiman]

Re: RCA L40FHD41 LCD was dead, replaced all caps on PB, now has no audio

If the amp output ic has issues it will take down the preamp (ground the signal).

Find the amp ic and it should have at least 12vdc going to it.

A good way to diag the output is to start in the middle. I do that by removing the output ic.

If the preamp signal shows up than you know you need output ic.

This may not be easy depending this tv`s audio circuit.

[2hamburgers]

Re: RCA L40FHD41 LCD was dead, replaced all caps on PB, now has no audio

Ok budm I see where you guys are trying to go now. Now im assuming i used powered speakers to plug into the audio out at the rca jack. I used Sony SRSD4 desktop speakers.........does that change anything? cadiman I get what you saying, but if you could clarify for me a bit: "A good way to diag the output is to start in the middle(middle of?). I do that by removing the output ic(desolder from the board?). Sorry if im frustrating anyone.

[budm]

Re: RCA L40FHD41 LCD was dead, replaced all caps on PB, now has no audio

If that SONY SRSD4 has the Green mini stereo phone plug on it and it does not have the RCA Line level audio inputs, then you will need cable adapter. Otherwise you should hear good sounds coming out for the SONY if the pre-amp in the TV is OK.
The RCA audio line out is there for you to be able to get better TV sound through your stereo system.

[cadiman]

Re: RCA L40FHD41 LCD was dead, replaced all caps on PB, now has no audio

Your doing fine, no worries.

The audio amp is part of the mainboard and I can`t get a close look at where to look without the board in front of me.

I would start by following the speakers leads board connector that should lead you to an output ic most likely surface mount.

There are lots of mainboards on feebay pretty cheap for this unit.

If you recapped the power supply you may just be missing a power feed to the mainboard via a solder issue.

I always assume it was something I did.

It works the same way with the wife.

[2hamburgers]

Re: RCA L40FHD41 LCD was dead, replaced all caps on PB, now has no audio

I wanted to say thank you to everyone that helped me with this problem. I am just too green at the moment to try to tackle this problem so I threw in the towel and bought another main board. It did in fact fix the television, and now its gonna pay some bills for me lol. Electronics is truly a complex science. You highly skilled persons here are exceptionally wise. I will continue to learn and maybe some day i might be able to make contributions to this forum. Again, thanks badcaps forum and members.