1. Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
    Dismiss Notice

TV Set 'Fails' Now and Then

Discussion in 'Repairing Electronics' started by MrAl, May 23, 2014.

  1. MrAl

    MrAl Well-Known Member Most Helpful Member

    Joined:
    Sep 7, 2008
    Messages:
    11,032
    Likes:
    952
    Location:
    NJ
    Hi again,

    Ok thanks. I dug into it again and replaced the other caps and now the repair is complete, except for the push button problem.
    I also did not realize it at first but two of the caps i had where slightly larger in diameter, so unfortunately they are now even closer to that transformer so there's no room for a heat shield. There was barely any room before anyway. I'll just have to wait and see how long they last like this, and if there's another problem i'll have to work that out then. I probably only have to get another 2 years or even less out of it now anyway.

    Also i thought i would mention that the two 2200uf caps that i already had were Panasonic :)
    The new ones i had to buy (1000uf) are Rubycon. All the caps are 105C and 10000 hrs, but it's interesting the one 1000uf i already had (to do the test with) was only 85 deg C, but that's replaced now too with a 105C unit.

    It will be interesting to see how long it lasts now that it has some good caps in there. In retrospect though, i think i should have measured the voltage being used with the caps in the circuit before committing to any particular parts. They are only rated 16v and i know the TV manufacturers like to push the envelope so maybe they are running them at 15v, but hopefully not. If i found out they were i could have ordered 25v units, as long as i could get them to fit in the confined space.
    Also a little interesting is two of each set of caps are in parallel. Two 1000uf's in parallel, and two 1500uf (now 2200uf) in parallel.

    Unfortunately though the problem with the push buttons still remains. I checked out the little PC board they use for the push buttons and it looked fine with no problems. The switches are very simple in operation, they simply ground a pin when they are pressed. There is no shorts or anything that could cause a problem, so i have to guess now that it is noise that is getting into the microcontroller that detects the switch closures or else they are not properly debounced. When either of the volume buttons is pressed the input source (TV, HDMI, etc.) switches by itself and of course it should not do that. If i have it set to HDMI for example when i press "Volume up" or "Volume down" it switches to TV input, which is the antenna, which is not right as it should stay on the HDMI input source.
     
  2. tvtech

    tvtech Well-Known Member Most Helpful Member

    Joined:
    Mar 27, 2010
    Messages:
    3,166
    Likes:
    348
    Location:
    South Africa
    Hi Mr Al

    Simpler than you think....those little tac Switches cause loads of problems....makes some CRT sets look like the Microprocessor has lost it's marbles.

    Solution: Buy a can of Switch cleaner...and spray that into/onto the switches one at a time while pushing them on and off rapidly...works here. Takes patience but is worth the while...

    Try it Buddy :)

    Regards,
    tvtech
     
  3. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

    Joined:
    Nov 17, 2003
    Messages:
    39,234
    Likes:
    641
    Location:
    Derbyshire, UK
    I can't tell from the picture where the switches are?, but if they are on the top of the set I've had two Sony sets, both the exact same model, with something spilt in the buttons on the top - causing them to do weird things. It's worth a go at trying cleaning, but in my experience such switches generally don't clean well.

    Going back a LONG time (KV2212 era) Sony used to use switches mounted on the top of the set where the switch used a rubber disc as the return 'spring' - the rubber would split, and the button fall down, closing the contact - I've changed hundreds of them :D

    No good changing just the faulty ones, if you did that they just came back a few weeks later with another one gone, so I used to change the lot.
     
  4. dave

    Dave New Member

    Joined:
    Jan 12, 1997
    Messages:
    -
    Likes:
    0


     
  5. tvtech

    tvtech Well-Known Member Most Helpful Member

    Joined:
    Mar 27, 2010
    Messages:
    3,166
    Likes:
    348
    Location:
    South Africa

    Hi Nigel

    The tac switch problem has been getting worse lately...causes crazy to stuff happen...set starts Auto Searching and half way through that decides to shut off/go into standby. And other weird stuff...

    I think Mr Al will be fine if he just cleans them patiently with a Switch cleaner....some take a while but...it is worth it.

    Strange hey...the whole tac switch problem was not heard of here in 2007 when I came back here.....I had to try and figure it out myself when it started a Year later in 2008....

    Money for jam now....It always looks like the Micro has gone nuts.....

    If I had to charge for Micro's that others change to try and fix the problem, I would be a very rich person by now....luckily I don't work that way.

    Who could think that a stupid friggin cheap push button switch could cause chaos and make the Micro look ill/sick/crazy.

    Anyway, glad I could share this.

    Regards,
    tvtech
     
  6. MrAl

    MrAl Well-Known Member Most Helpful Member

    Joined:
    Sep 7, 2008
    Messages:
    11,032
    Likes:
    952
    Location:
    NJ
    Hi again,

    I have included a picture of the switches and board they are mounted on.

    As you can see, these are small tac switches but they are independent and are not made by the manufacturer of the tv.
    Yes they are cheap ones, but they usually dont go bad especially since i've hardly used them in the whole life of the set.

    The way it looks like they work is when you press one, it grounds it's secondary terminal. The primary terminal is always grounded on every switch, so it makes a contact between it's other terminal and ground and that must tell the uC that the switch was closed. The connector and wires bring the signals to the main board, and the cable run is rather long being at least 12 inches.

    As you can see the volume switches are on the left side of the board, and the "Enter" switch is on the far right. That made it seem strange that one switch so far away from the other could cause a problem with the other, but then i found out that when you press the channel switch (up or down) THAT causes the ENTER function to execute, so that means that it's not the enter function it's the channel function that is being executed, and that's right next to the volume switches. So all along it looked like the "Enter" function was being executed (by cross talk between the volume switches and the Enter switch) but now i see it looks like some sort of cross talk between the volume switches and the channel switches. But either volume switch can cause the problem.
    And normal operation by pressing either channel switch on purpose always causes it to go to TV channel 9 when it is originally on HDMI input.
    This makes it hard for me to believe that it could be a dirty switch. These kinds of switches are normally open type, and you really have to press one to get a contact. It's hard to believe that one could close all by itself, unless it was damaged, and then it might take less force to close it.
    I suppose i could solder wires on to one of the volume switches and see if connecting the wires together causes the same problem. If there is no physical movement involved on the circuit board then i would seriously doubt that it could be a switch problem.

    It was hard to trace out the circuit path because that connector was in the way of seeing the board properly, i guess i should have gotten out the ohm meter, but i really had hoped to see the paths and how close they were to each other.
     

    Attached Files:

  7. tvtech

    tvtech Well-Known Member Most Helpful Member

    Joined:
    Mar 27, 2010
    Messages:
    3,166
    Likes:
    348
    Location:
    South Africa
    Hi Mr Al

    Some things can not be logically understood. It does not help using a Multimeter for testing good or bad tac's....
    Your meter will not guide you.

    It does not matter if the tac's have not been used. Trust me on this. They need cleaning or replacement if not available...and lot's of patience if you decide to clean them.....please just try my advise anyway no matter how crazy and illogical it sounds...

    All it will cost you is a little can of switch cleaner. And patience.

    Regards,
    tvtech
     
    Last edited: Jun 7, 2014
  8. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

    Joined:
    Nov 17, 2003
    Messages:
    39,234
    Likes:
    641
    Location:
    Derbyshire, UK
    You're rather missing the point :D they go bad (contacts get dirty) exactly because they have never been used.

    They work by switching different value resistors to ground, so if the contacts are dirty (and so too high resistance when pressed) then you get the wrong value resistance presented, so the micro thinks you've pressed a different button. It's a VERY common problem.
     
  9. MrAl

    MrAl Well-Known Member Most Helpful Member

    Joined:
    Sep 7, 2008
    Messages:
    11,032
    Likes:
    952
    Location:
    NJ
    Hi again,

    Ok then i guess i'll have to try an experiment. I'll solder two wires to one of the volume switches. I'll use a brand new switch or just short the two wires and see if it works without a problem that way.

    I dont really have any switch cleaner on hand, but i think i still have some general purpose cleaner spray. I'll have to see if i still have it.

    I do have some new tac switches around, quite a few actually, and maybe even those very same size and lead spacing.

    I would not even care if i had to mount two brand new switches myself and just not use the old ones anymore. No problem there.
     
  10. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

    Joined:
    Nov 17, 2003
    Messages:
    39,234
    Likes:
    641
    Location:
    Derbyshire, UK
    Don't you have WD40?, I've been using that in preference to switch-cleaner for decades now, it's far better at cleaning switches and controls.
     
  11. killivolt

    killivolt Well-Known Member

    Joined:
    Mar 12, 2008
    Messages:
    3,212
    Likes:
    121
    Location:
    U.S.
    GP cleaners sometimes are to harsh and can melt some plastics; use WD40 like Nigel said. He suggested it to me sometime ago when I had tuner problems on my guitar amp. Works well.
     
  12. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

    Joined:
    Oct 30, 2010
    Messages:
    9,918
    Likes:
    1,098
    ONLINE
    tvtech:

    Unless someone used some precious metals on the contacts, you really need to pass about 1-10 mA through them to "clean" the contacts. Unfortunately, that's the job of the designer, not you. I designed something for a research setting and had to use mercuty wetted relays. The price has gone up considerably. http://www.newark.com/coto-technolo...pst-no-5vdc-2a-thd/dp/87F145?MER=BN-PG-87F145 One of the ranges was 1uA full scale.
     
  13. MrAl

    MrAl Well-Known Member Most Helpful Member

    Joined:
    Sep 7, 2008
    Messages:
    11,032
    Likes:
    952
    Location:
    NJ
    Hello again Nigel, killivolt, and KISS,


    Thanks for the suggestion to try WD40, and yes i do have that around here somewhere.

    I am aware that mercury wet contacts are used in relays that have to pass small currents, and that the switches will not have this feature. What i did not know until Nigel suggested it was that they may be using reverse analog multiplexing for the switches, as i originally jumped to the conclusion that they would be using a digital technique. I can prove this using a couple wires and a pot, where i should be able to 'tune' in any of the several switch functions with the pot using only a single switch, but maybe i'll just try shooting it with a couple shots of the WD40 and see what happens. I can try one switch at a time and observe the results right away.
     
  14. tvtech

    tvtech Well-Known Member Most Helpful Member

    Joined:
    Mar 27, 2010
    Messages:
    3,166
    Likes:
    348
    Location:
    South Africa
    LOL..this is funny :). I suggested cleaning the switches to start with....and then I am conveniently ignored..

    No sweat. Been there before where intelligent people get simple, straightforward answers to an "apparently" complicated question....and then do not trust or believe the advise given...."because it is too simple"....:D:D

    Mr Al

    Step 1. Disconnect the Tac's switching pins with a solder sucker...all of them one Tac at a time. So now, as far as your TV is concerned...it has no tac switches.
    Step 2. Turn the TV on. See if nothing crazy is happening...like if you are maybe on Video and it stays there....nothing else.
    Step 3. Reconnect one Tac at a time....until the problem comes back...and you will of nailed the one screwing up everything.

    If you want your TV to work tonight, you would or should maybe follow this simple advise from a simple tvtech...I deal with this stuff daily....

    The choice is yours.

    tvtech
     
    Last edited: Jun 15, 2014
  15. killivolt

    killivolt Well-Known Member

    Joined:
    Mar 12, 2008
    Messages:
    3,212
    Likes:
    121
    Location:
    U.S.
    I'm glad this subject came up; I had no idea the problem even existed until now? Now I know and how to solve it :smug:

    However, I observed you suggestions:rolleyes: As everyone else did I'm sure. Great advice; it will be nice to have you around when my samsung drops dead some day > :grumpy:


    I hope all is well in SA and your partner on the bench is still working out:D
     
  16. tvtech

    tvtech Well-Known Member Most Helpful Member

    Joined:
    Mar 27, 2010
    Messages:
    3,166
    Likes:
    348
    Location:
    South Africa
    Hi KV

    SA the same but my partner on the bench is awesome. Only contracts here one or two days a Week...when I am a bit flooded with sets....hey, the best there is. He knows his stuff and I am flat out happy to work next to him.....we get along very well...crazy amazing difference to what I had before....

    Like chalk and cheese. Day and Night. Wonderful.

    Stay well Buddy,
    tvtech
     
  17. MrAl

    MrAl Well-Known Member Most Helpful Member

    Joined:
    Sep 7, 2008
    Messages:
    11,032
    Likes:
    952
    Location:
    NJ

    Hi,

    Ignored? Never :) Overlooked perhaps.

    Did you suggest WD-40? I thought you meant another type of cleaner which i dont have anymore. I had some 'regular' cleaner way back then, but dont have that anymore and didnt feel like buying any. But when Nigel suggested WD-40 my eyes lit up a little more because i happen to have some of that, around somewhere.

    Just to note, the troubleshooting you suggest will have to wait because it means taking ALL those screws out AGAIN, and i dont think i want to do that right away. But i can reach the switches through the back panel with a spray can cleaning tube, so i will try that.

    Sorry if you felt ignored, as i am sure it couldnt have been me, unless i missed something though, and you'll note that in my sig line i suggest PM'ing me if i miss something you (or anyone else) said that you (or anyone else) thinks is important.

    Thanks again for the suggestions.
     
  18. tvtech

    tvtech Well-Known Member Most Helpful Member

    Joined:
    Mar 27, 2010
    Messages:
    3,166
    Likes:
    348
    Location:
    South Africa
    Hi Mr Al

    I never meant to chirp too much....thing is...the repair is taking way too long.
    I would have liked to see all up and running long ago. :(. I am like that with rush/easy jobs like maybe your one???

    Hey, maybe you will learn from this......

    I try and teach people that if they have to take a thing apart (lots of screws and time and stuff) to fix something like a simple Aerial socket..they might as well check the PCB for dry joints too while they are at it.....

    I know how you feel though. You do not do this on a regular basis...and to take a flipping thing apart again is a mission...for a pesky tac switch is nothing but pure irritation....

    So, I suggest this: When you find the time to take the whole thing apart again....PM me or post here. I am more than happy to help. We will go through it together and joke and fix it and the problem will be solved.

    Looking forward to it :)

    Regards,
    tvtech
     
  19. MrAl

    MrAl Well-Known Member Most Helpful Member

    Joined:
    Sep 7, 2008
    Messages:
    11,032
    Likes:
    952
    Location:
    NJ
    Hi again,

    Well after the caps got replaced the rush was off. I have time to fix it, as long as i need, so there's no rush now. When the caps went it was another story though because i either had to get it fixed or go out and get a new TV or wait for a delivery from an online outlet. But now that they are completely replaced, i dont have to rush especially because i dont need to use the buttons that often. It's just that when i do have to use them it can be annoying.

    I was also going to dig into it further when i took it apart to do the final cap replacement, but i changed my mind when i found out it was going to be much more involved to get into the next level of the guts. It appears that they are using one of those poly connectors for something and taking that apart means it may be very hard to get back together, along with another set of screws (ha ha).
    So i never got to actually see the bulbs, but that's the way it goes.

    I also saw something on the web a while back where the guy replaced his tube bulbs with white LEDs. That would be interesting to do too, but not easy with this stupid set.
     

Share This Page