Question about RCA F25305 25" TV

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RCA F25305 25" TV: sound dissapears, channels 20 to 29

RCA F25305 25" TV: When the TV is turned on and left at channels bellow 20 or over 29 the sound and picture is perfect. As soon as we put the tuner at a channel between 20 and 29, the picture stays OK but the sound becomes "snow" after 5 to 10 minutes of the channel change. The TV is directly connected to the Cable,
The Coil AFT and the IC switching AGC were changed without results.

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  • 24 more comments 
  • Andre Taillefer Feb 22, 2009

    Although a technician, I'm more in computers. I brought the TV to a local expert and he has the TV for 4 months, without finding the problem. I don't have the service manual and the repair center have it, but paper so kinda hard to send it to you. I was hoping to find in you guys some ideas that I could bring to the service center for them to try. They told me that they lack ideas on how to solve the problem. They told me it could be a faulty design from RCA. But then, why did it took many years before doing the problem??!!

  • Andre Taillefer Feb 22, 2009

    -check the cable connections, also all input and output wire connections.
    -better to call your cable provider.

    Both suggestions aren't considering the fact that it works fine bellow 20 and over 29. Also the TV was tried at 3 different places, all directly connected to the Cable.

  • Andre Taillefer Feb 22, 2009

    I have been suggested that : ..the output power transistors is failing from heat..." But then why would the sound works for hours WITHOUT failing and as soon as we tune a channel from 20 to 29 it would lose sound within minutes??? I don't think a transistor heat would be the problem, unless you prove me that some transistors works only on certain channels and not on others.

  • Andre Taillefer Feb 22, 2009

    I forgot to say that to solve the problem I have to unplug the TV from the wall and replug it, for the sound to come back.The sound will then stay for as long as I don't re-tune a channel from 20 to 29.

  • Andre Taillefer Feb 22, 2009

    I was suggested to: "check all conections and let me know". If you read carefully all the posts I did you will notice that it can't be a connection problem. Of course, all internal and external connections ARE tested and considered as perfect.

  • Andre Taillefer Feb 22, 2009

    It was suggested: "It sounds to me as a Wire Connection, but check all the settings in the TV menu".
    The menu was checked hundreds of times!!! Wire Connection??? If you mean the cabling, again, it's not that, as mentioned in previous posts.

  • Andre Taillefer Feb 22, 2009

    MESSAGE TO: welcomejee
    Your post is cut before the end. What is the rest, please???

    "...change ceramic filters of sound IF, normally these are 2__________

  • Andre Taillefer Feb 22, 2009

    MESSAGE TO: welcomejee
    Your post is cut before the end. What is the rest, please???

    "...change ceramic filters of sound IF, normally these are 2__________

  • Andre Taillefer Feb 23, 2009

    I have been suggested, by 2 different persons, to change the filters. Can someone be more precise on those filters?? One said "ceramic filters". Are they ceramics Capacitors?

  • Andre Taillefer Feb 23, 2009

    The suggestion of looking on the web sitehttp://wa6ati.com/CTC203.html didn't help as it doesn't contain any trouble similar to mine.

  • Andre Taillefer Feb 24, 2009

    The proposed comments and solutions of FIXE_YOU aren't useful for the problem I have.

  • Andre Taillefer Feb 24, 2009

    It was said that:" It sounds like the "Filter" is bad on the trunk line. Call the cable company and ask them to have a look."
    Again, as mentionned in one of my previous posts, the TV was tried at 3 different places. Those 3 places are in 3 different cities so IT CAN'T be a cable filter problem. Furthermore, a filter problem would cut the sound AND picture, BUT I KEEP THE PICTURE. The only thing that goes is the sound, and only after about 5 minutes after the selection of a channel between 20 and 29.

  • Andre Taillefer Feb 24, 2009

    The text of "APremkumar" is not helpful.

  • Andre Taillefer Feb 26, 2009

    I was suggested to have the board of the TV to be checked by checking units at the repair center. The repair centers in my city don't have such machines.
    Also, I will repeat that if the TV is on channels under 20 or over 29, everything is fine... always.

  • Andre Taillefer Feb 26, 2009

    Again, I was told by "jonb3838" to check the Cable. I will repeat that it was tested on 3 different cables, in 3 different cities. IT'S NOT THE EXTERNAL CABLE!!!

  • Andre Taillefer Feb 26, 2009

    I was told by "localwonder" that 4 parts are to be change and it will solve the problem. I will try it!!!

  • Andre Taillefer Feb 26, 2009

    The precisions of "welcomejee" is VERY appreciated. I'm in the process of trying the filter ceramics.

  • Andre Taillefer Feb 26, 2009

    Again the comment of "dragonsthatk" about the external cable is not useful because the TV was tried at different places.

  • Andre Taillefer Feb 26, 2009

    Again, again and again... it's not the CABLE as "simard2" seems to think.

  • Andre Taillefer Feb 26, 2009

    Thanks very much to "ginko" for the pricisions on the filters.

  • Andre Taillefer Feb 26, 2009

    Again, the cable IS NOT THE PROBLEM... as "sizemoreboy" suggest!!

  • Andre Taillefer Feb 26, 2009

    "emjem74" proposes to try "... an external sound device with this problem as it sounds to me like it could be the set itself as apposed to the channels...". It an interesting thing to try, but... I still don't see what would be the link with some specific channels and not with others. Don't forget that the TV can work HOURS, DAYS, WEEKS... without loosing the sound, as long as I don't choose a channel between 20 and 29.

  • Andre Taillefer Mar 01, 2009

    Again, "ioant27" is suggesting to check the cable provider. Obviously, he didn't read me numerous posts about it.

  • Andre Taillefer Mar 01, 2009

    Thanks to ginko for the professionnal post. We are now in the process of trying his suggestions.

  • Andre Taillefer Mar 01, 2009

    the web link of "APremkumar" was already given by someone else. Thanks.

  • Andre Taillefer Mar 01, 2009

    "blueextc3221" proposes a video processor problem. I'll remember it but I really don't think it will help.

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19 Answers

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Hello taiandre,

I give you some suggestions based on having dealt with this kind of problem before. First of all, you need to isolate the possible causes, here is a procedure for that:

You must have a RF-IF signal generator to do this isolation test, tune your TV to channel 2, tune the signal generator to channel 2 an set the video out put to color bars and the audio out to 1KHz. You should see color bars and hear a 1KHz tone. do this for channel 5, 4, 7, and 9. Then tune your TV to channel 20 and set the signal generator for channel 20, do this for all of the channels between 20 - 29.

Now for the reason, you have to isolate this problem to determine if it is an RF or IF problem. The outcome of this test is to see if the audio cuts off when you use a know good signal (the RF-IF generator)

The next test is to set the RF-IF generator to IF and inject the same signal only at the IF (post tuner) ranges. You will have to inject the signal at the first IF point (usually after the tuner) and see is the IF injected signals have the same problem, if they don't, then the problem is in the tuner stage and you will just have to replace the tuner. If the test shows the problem still occurs after the tuner, then this becomes an IF issue and you can inject the signal and by using an oscilloscope you will be able to trace the signals through the IF/AUDIO stages to see where they are dropping off. Personally I believe that this is a tuner issue, but the only true way to tell is by using proper troubleshooting technique.

Because until now what I have seen is a lot of shotgunning, and that works sometimes but this problem needs actual troubleshooting to be done.

The Signal Generator (I use the Sencore VA62A) will give you a know good reference source,

The Oscilloscope (I use the Sencore SC3100 and the SC61) Will give you a way of looking at the waveforms you need to see to help you diagnose this problem.

Now, If you don't have the equipment mentioned above then don't bother trying to troubleshoot this problem, because these are the tools you will need, to do the job properly. In this case take the TV to a TV repair shop and inform them that you believe that the tuner is malfunctioning, and you would like them to use an RF-IF generator or a Universal Video Analyzer to test if the tuner is working and to isolate the problem between the RF and IF sections of the TV.

I would rather not be rated if you do not like this suggestion, I am basing my suggestion on sound troubleshooting methods, and I understand that these methods are not what people are looking for, but they are what has to be done.

I hope this helps

Shuttle83

http://www.electron-age-technologies-llc.com

Posted on Mar 01, 2009

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  • Master
  • 15,935 Answers

Have you tried a different connection method to your cable? IE - a cable box with component outputs? Or in a different room to eliminate the source wiring as the problem?

Unfortunately it sounds like the video processor chip is at fault. This is a nasty chip to change as it has something like 40 pins on it and is soldered in. You may have a cracked solder joint or a previous repair's lousy soldering job and the results of that are now being seen due to thermal stress as it warms up between a certain channelset. The processor chip is - fortunately - cheap, it sells for between $ 10-15 but putting it in properly really calls for a vacuum desoldering station, which is an expensive tool which not every repair tech has.
In any case, I don't think there's any solution other than either resoldering the chip pins or replacing it.
You probably have a combination of problems With the Tuner and Processor. I would suggest another repair center if they have had the set 4 months and cannot root out the problem!!

Thanks for using FixYa - a Fixya rating is appreciated!!

Posted on Mar 01, 2009

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  • 63 Answers

First of try moving the TV to another coaxial output and see if you are able to catch the channels from there. If no luck, then contact your Cable Provider Company and tell them about your problem. If you can watch TV in one room and not in the other there might be a problem with the connections of cables inside your house. Hope I Helped!

Posted on Feb 26, 2009

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Have you got any external sound devices you could try with this problem as it sounds to me like it could be the set itself as apposed to the channels, if problem goes away with external sound eevice then you can guarentee the set to be faulty sound card, and this is not easy fix

Posted on Feb 26, 2009

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  • 76 Answers

Hi, This sounds like it a problem with the cable and not the TV . I would recommend calling your cable company and have them come out and check you cable box for a bad wire.

Posted on Feb 26, 2009

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Hi there, i did some research and found four parts that are defective in this model run. I have placed the model numbers on the side of each part and, you can purchase each part online if you would like. Click here for the parts store.


IC - EEPROM - (244878)
TUNER- (247225)
TXSTR- (482213060373)
DIODE- (198589)

Posted on Feb 24, 2009

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  • 237 Answers

The problewm is not with your tv at all its going to be 2 things the cable line or the cable service. There Is a bad wire either coming in the house or inside the house. Call your cable company. They will be able to resolve the issue

Posted on Feb 24, 2009

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Get you board main circuit board checked at the tv repair center.as they have checking units with then as the board is connected to the checking machine the faulty part will get detected and that component has to be replaced.as if you r sayionmg at all the remaining channels the picture and sound is perfect.only at few channels between 20 -29.and as if its the problem od filters and capacitors they are not at all too costly to get it replaced.the reparing cost will be negligible.

Posted on Feb 24, 2009

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  • RCA Master
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As said already, test the ceramic filters, or IC on IF circuit.
Function of filter is to attenuate bad signals, as video and sound IF components otherwise capable of interfering with and distorting the input television signals.
Between the tuner signal input, and the amp final there are two IF stages.
If filters can fail at at determined frequencies and that is the cause for your problem.
To test and locate the if filter I suggest buying a service manual for this model.
This is an example.
Here you can buy the download for the service manual for your model: Thomson RCA TV Television Service Manual pdf F25305
Below there is also link to whole tuner board replacement for your model.
247225

Posted on Feb 24, 2009

  • 2 more comments 
  • Ginko
    Ginko Feb 24, 2009

    It is not the cable filter, it is one of the two IF stages, either on TV or on receiver box.

    I re-post my last comment, read also welcomejee.

    As said already, test the ceramic filters, or IC on IF circuit.
    Function of filter is to attenuate bad signals, as video and
    sound IF components otherwise capable of interfering with and
    distorting the input television signals.
    Between the tuner signal input, and the amp final there are two IF stages.
    If filters can fail at at determined frequencies and that is the cause for your problem.
    To test and locate the if filter I suggest buying a service manual for this model.
    This is an example.
    Here you can buy the download for the service manual for your model: Thomson RCA TV Television Service Manual pdf F25305
    Below there is also link to whole tuner board replacement for your model.
    247225


  • Ginko
    Ginko Feb 24, 2009

    And also , a ceramic filter is not a Capacitor, they usually work on a Piezoelectric principle and can filter certain frequencies, they are used in different circuits with different purposes.

  • Ginko
    Ginko Feb 24, 2009

    Ceramic filters come in different shapes, see the link below:

    CERAMIC FILTER (CERAFIL ).

    To locate the IF circuit you need to buy the service manual, or to have enough experience on TVs to find it at a glance.

    Thomson RCA TV Television Service Manual pdf F25305




  • Ginko
    Ginko Feb 27, 2009

    Let us know if you have found the fault on your TV.

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  • 564 Answers

Hi,
Check the Wire connection and if you have any other speakers try to connect and check.

Hope This Helps!!!  Please Rate my Response!!! Thanks!!!
PREM


Posted on Feb 23, 2009

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  • 164 Answers

It sounds like the "Filter" is bad on the trunk line.
Call the cable company and ask them to have a look. How far from the cable's "NODE" are you?

Posted on Feb 23, 2009

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  • RCA Master
  • 1,800 Answers

If u r defintely sure from the settings of TV: especialy a feature nammed Guide+ that locks some chanels check it in tghe manual.

then a shematic of TV's Tune Ic is needed to change any shorting out or defective part also check the provider before taking tv apart.

Posted on Feb 23, 2009

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  • 2,267 Answers

Click here to find more info if you have a CTC203 chassis.

Posted on Feb 23, 2009

  • Jaime Hernandez Feb 23, 2009

    Capacitors are known as filters as well. Ceramic is the material they are made of. If you check the link provided, you will see that most audio related failures are due to a defective ceramic filter/capacitor(s).

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  • 326 Answers

Its the board problem in your tv get it checked .the sound filters on the tv are near to its end can be getting faulty.so its not supporting some channels and supporting some channels.that has to be replaced.get it repaired from any local repair shop,

Posted on Feb 23, 2009

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  • 124 Answers

It sounds to me as a Wire Connection, but check all the settings in the TV menu. Let me know.

Thank you for using Fix Ya!

Posted on Feb 22, 2009

  • Frank Simard
    Frank Simard Feb 23, 2009

    Yeah, what micromaster said, call your Cable Provider.

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  • 547 Answers

This is a conection problem please check all conections and let me know

Posted on Feb 22, 2009

  • albert getty
    albert getty Feb 22, 2009

    some times the cable wires are not made right do you have same problem with dvd or vhs on channel 3?

  • albert getty
    albert getty Feb 26, 2009

    do you have it hooked to a digital box? If no it may be the cable in to your home

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OK, sounds you are TV tech or repairing TV at yourself. Great.
I do not have related service manual and if you have, please email me at welcomejee@yahoo.com so I will help you out to rectify problem.

Problem should be in tuning section in TV.

Posted on Feb 22, 2009

  • 2 more comments 
  • Shahid Electronics
    Shahid Electronics Feb 22, 2009

    It looks problem in Sound IF stage and you can guide service guys to check / change ceramic filters of sound IF, normally these are 2


  • Shahid Electronics
    Shahid Electronics Feb 22, 2009

    I would recommend to replace Sound Filters in sound IF section.



  • Shahid Electronics
    Shahid Electronics Feb 23, 2009

    It looks problem in Sound IF stage and you can guide service guys to
    check / change ceramic filters of sound IF, normally these are 2 installed in IF stage to filter sound carrier waves and extract sound frequencies.

  • Shahid Electronics
    Shahid Electronics Feb 23, 2009

    Following is an image of ceramic filter..



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Hi there,

check the cable connections, also all input and output wire connections.

Posted on Feb 22, 2009

  • micromaster
    micromaster Feb 22, 2009

    better to call your cable provider.

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  • RCA Master
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Sounds like one of the output power transistors is failing from heat, as the demand to amplify the sound increases the heat increases, this is when all electronics start to show problems of breakdown, i.e. heavy heat load.

Posted on Feb 22, 2009

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