need help - Page 1
Forum section: electronics / repair

author: kjn4685
author_rank: Regular Contributor
timestamp: March 04, 2015, 02:26:49 am
content: I have a 26" sylvania tv that has no sound. I have found out the voltages are not right and so I changed the mosfet # 2sk3561. because the voltages on the manual says the voltage on the mosfet could be if I am reading it right The schematic says on the gate is 5.3v drain 134.5v sources 0.1v these all are acv. I am really beating my head against the wall I have been working on this for about month.i can not figure ou to put the service manual on this site could you guys help out.

author: kjn4685
author_rank: Regular Contributor
timestamp: March 04, 2015, 03:03:11 am
content: What I mean that the site tells me that it has time out, but I think it is the size of it.

author: Zucca
author_rank: Unknown
timestamp: March 04, 2015, 07:10:21 am
content: With the information you provided... all I can say is check the power supply rails of the audio circuit.In your position I would have attached pictures of the boards, of the #2sk3561 in the circuit and the quote of the manual. On top of that also the model number of your tv could be nice to know.Right now to help you I need to get my hands on a 26" sylvania tv, hoping is the one you are talking about, and then open it up to understand what you did...

author: kjn4685
author_rank: Regular Contributor
timestamp: March 04, 2015, 10:29:39 pm
content: I tried to put the service manual on the forum , but it says that is to big in kbs

author: kjn4685
author_rank: Regular Contributor
timestamp: March 08, 2015, 11:33:09 pm
content: Here is the pics of my sylvania 26" tv. model # lc260ss1. I finally figure out how put this on the forum.

author: kjn4685
author_rank: Regular Contributor
timestamp: March 17, 2015, 09:56:58 pm
content: Guys I need help. If you guys can help me out I would appreciate it very much. I said in my previous post I am trying fix this tv , but I know that for you guys to help me you need the service manual. I can't figure out how to download the pdf file if you can help me me. So if can show me the way to do this I would appreciate it very much.Thanks in advance.

author: dtnicholls
author_rank: Contributor
timestamp: March 18, 2015, 09:20:35 am
content: Start with measuring the ESR of all the caps mate, 95% of all the faults I see on LCDs (that aren't related to physical damage) are just bad electrolytics.Can you get a few good hi-res pics of the boards from various angles?

author: kjn4685
author_rank: Regular Contributor
timestamp: March 18, 2015, 07:16:32 pm
content: here is the pics of the boards

author: Seekonk
author_rank: Super Contributor
timestamp: March 18, 2015, 08:30:15 pm
content: If the TV is totally dead, that FET could be the problem otherwise it should be fine.. If it has external audio jacks, does audio come out of them?

author: kjn4685
author_rank: Regular Contributor
timestamp: March 18, 2015, 09:48:20 pm
content: No it does not come out of the composite audio. I check the speakers and they check out alright.

author: dtnicholls
author_rank: Contributor
timestamp: March 19, 2015, 10:28:34 am
content: So, I assume you've checked the fuse?Does the TV turn on? Does the power light just blink on and off? Does everything look normal but show no picture? Basically, what's it doing...Next question, what voltages do you have on all the supply rails? These need to be measured with everything plugged in (ie, they need a load)What is the serial number on the back of the TV, there are a few different versions of the power supply in that TV model, the serial number tells you which one you have.Please be as specific as you possibly can be. The better the information you give, the more accurate the response can be.

author: kjn4685
author_rank: Regular Contributor
timestamp: March 19, 2015, 05:49:49 pm
content: Yes I have checked the voltage rails and not all of them are right. The fuse is ok. The model # lc260ss1.and I have been checking the voltage with the board out of the tv. The tv does turn on and the picture is fine.

author: kjn4685
author_rank: Regular Contributor
timestamp: March 19, 2015, 08:32:15 pm
content: As I said the tv turns on and there a picture , but no sound. The s/n is 2sa2a1028103001. One of my concerns is the voltage on the mosfet. I get 51vac on the drain. If this is not a enough information let me know.

author: Seekonk
author_rank: Super Contributor
timestamp: March 19, 2015, 09:24:17 pm
content: This is likely a problem with your meter not being able to read this pulsed signal. Pretty much guarantee you are wasting your time looking at this part if you get video. If you are not getting audio at the jacks then the problem is the audio detector.

author: kjn4685
author_rank: Regular Contributor
timestamp: March 19, 2015, 10:49:08 pm
content: Ok what kind of meter do you suggest.

author: Seekonk
author_rank: Super Contributor
timestamp: March 20, 2015, 02:43:08 pm
content: All these posts and you haven't taken a logical approach to the problem. A free Harbor Freight meter is good enough to fix about anything. You have a picture so that says the main power supply, tuner, IF are all working. You don't have audio at the jack. That means the amplifier doesn't matter since sound doesn't get to it. That leads you to the area of the detector between the IF and the audio jack. That is if you actually tested the RCA audio output.

author: dtnicholls
author_rank: Contributor
timestamp: March 21, 2015, 01:27:55 pm
content: For looking at audio, a cro.Do you have audio at all? Have you tried on a HDMI input or composite input? Have you tried the audio outputs as well as the speakers?If you have no audio at all, I'd start by hooking up a sig gen (1khz sine wave) to the L and R audio inputs and just chase down the signal with a cro. You should be able to find it at the mux and then follow it through to the processor and from there back to the amps. When you find where it disappears then you've got a good place to narrow down your search.It goes something like this:The audio inputs go to IC771 (TC4052BF), which selects between them (outputs on pin 3 and 13, L+R respectively) and sends them off through CN302 (pins 13 and 11) to the main processor board.Chances are that this part of the circuit is all working fine though, cause this only handles audio inputted to the TV, not audio that's been received through RF, so assuming you've no audio at all this should all work fine.From there the audio goes from the main processor back to the power supply PCB through CN301.For the audio outputs on the back of the TV, the audio goes through pins 2 and 4 (again, L+R respectively), through IC871 (op amp with a small gain) and to the output jacks.For the speakers, audio goes through CN301 pins 6 and 8, and goes to IC801 (audio amp BD5426EFS) pins 1 and 44. Power supply for the amp is 13V on pins 29 and 30 (doubled up, they're internally connected).See how you go with that and let us know your results.

author: kjn4685
author_rank: Regular Contributor
timestamp: March 21, 2015, 08:36:47 pm
content: Forgive me for this stupid question. What is a cro. No there is no audio. I have checked the composite audio still no audio. I changed the speakers and they work.

author: kjn4685
author_rank: Regular Contributor
timestamp: March 21, 2015, 09:45:41 pm
content: You mean a oscilloscope don't you. For the 1kHz signal could I use function gen.

author: dtnicholls
author_rank: Contributor
timestamp: March 23, 2015, 08:38:41 am
content: You want a function (signal) generator to generate a sine wave and input it to the composite inputs at 1Vp-p.You want a cro (oscilloscope) to look at that signal and chase it through the circuit until you find the bit that's broken. You can use a multimeter (set to measure ACV) but it's a bit harder and the wrong result can be obtained if you're not careful. Note that a multimeter is going to give you results in RMS, not p-p.

author: kjn4685
author_rank: Regular Contributor
timestamp: March 23, 2015, 07:17:31 pm
content: Thanks to everyone who has help me with this. I will let everybody know how things turn out.

author: kjn4685
author_rank: Regular Contributor
timestamp: March 24, 2015, 01:22:01 am
content: Nicholls thanks for information, but I have a question can I unhook the lcd part of the tv. So that I can test the chips on the bottom.

author: kjn4685
author_rank: Regular Contributor
timestamp: March 25, 2015, 12:20:22 am
content: Hey thanks to everyone who has help me I got it fixed. The problem was in the audio amp was it.

author: dtnicholls
author_rank: Contributor
timestamp: March 25, 2015, 11:58:38 am
content: The amp itself had failed? Or something else?

author: kjn4685
author_rank: Regular Contributor
timestamp: March 25, 2015, 06:00:29 pm
content: It was in the circuit of the op amp. The transistors q801 &q802 in the audio mute there was a bad solder joint. That is all I could find. Again thank you very much for the help you have given me.