sharp television no display.

Discussion in 'General Electronics Chat' started by imraneesa, Jun 19, 2015.

  1. imraneesa

    Thread Starter Member

    Dec 18, 2014
    184
    4
    Dear Sirs,

    I have sharp 27h-s60 crt TV which was functioning very good. then suddenly when we on it yesterday we did not get the display and some humming sound was heard.
    i opened the tv and checked the volates. i got good AC entering into 115V AC. and when i checked near filter capacitors and before that i on the television i did not get good amount of DC voltage on filter capacitors. i was getting very low voltages.

    and the ac current is directly connected to the transformer on the other side.

    i am in doubt that filter capacitor might be a fault? can anybody give me any ideas. now when i on the tv nothing happens, not even any sound.

    Please throw some light on this.
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,747
    759
    What is the DC voltage at filter capacitor ?
     
  3. imraneesa

    Thread Starter Member

    Dec 18, 2014
    184
    4
    As I on the power button it read 22v then it came down to 9v. Transformer giving output as 13v DC.
    The filter capacitor is 820uf and 200v.
     
  4. imraneesa

    Thread Starter Member

    Dec 18, 2014
    184
    4
    As I on the power button it read 22v then it came down to 9v. Transformer giving output as 13v DC.
    The filter capacitor is 820uf and 200v.
     
  5. electronis whiz

    Well-Known Member

    Jul 29, 2010
    519
    27
    I would guess capacitor issue. They seem to always fail in these things. They use some cheap cr@p capacitor brand like samxon, sanwha, etc then they fail. The hum you heard is probly either the PSU or the backlight inverter. Based on the output voltages I'd say you have some issue in the main PSU unit. My suspect would be the filter cap has become low impedance thus dropping the output.

    What I would do is take your PSU board remove everything from it except the control buttons for power, etc. Turn it on see what output is if normal then you have a short elsewhere. If still wrong outut I'd remove the caps measure again see if you get close to the proper DC output.
     
  6. bwilliams60

    Active Member

    Nov 18, 2012
    722
    88
    Couple of questions. On the perimeter of your power supply you will find IO connectors with voltages marked on the board. You need to check all these voltages to see if they are what they should be. My first question should be as to whether or not you qualified or capable of measuring these voltages as there are components in this set that can kill you or at least knock your socks off. If you are not familiar with TV's, you may want to do some reading or hire a professional to look into it.
    Secondly, true a lot of televisions have capacitor problems but you need to know what to look for before condemning them. the first sign would be a bulged top. Second may be leakage around the cap and the true way of checking them is with an ESR meter. Check your voltages first.
     
  7. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,747
    759
    Post some pictures.
     
  8. sheldons

    Active Member

    Oct 26, 2011
    616
    101
    Nonononono.......if you have limited servicing knowledge and no service manual you will end up going round in circles....post a photo of the chassis used in your set....then people may talk you through the necessary steps in order to find out what is wrong
     
  9. imraneesa

    Thread Starter Member

    Dec 18, 2014
    184
    4
    here are the photos of the board.
    [​IMG]

    [​IMG]
     
  10. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,747
    759
    You need to post closeups.
    I believe you have a stby transformer.
    Measure the AC voltage at primary and secondary of transformer
     
  11. sheldons

    Active Member

    Oct 26, 2011
    616
    101
    Ok ......first things first check the power supply actually works by either removing the lopt and line op transistor or remove the feed to the line op stage ....load the ht line with a lamp,40w, switch on and check the ht supply is present. . if you had a scope and isolation tx you could also check line drive is present. ...
     
  12. ian field

    Distinguished Member

    Oct 27, 2012
    4,413
    782
    That's what I thought when I looked - so where's the main chopper transformer?!

    Some sets combined the SMPSU with the horizontal output stage - but I thought that died out in the 90s.

    They can be a real pig to troubleshoot!
     
  13. ian field

    Distinguished Member

    Oct 27, 2012
    4,413
    782
    Just looked again at the screen print on the solder side - the isolation barrier marking splits the horizontal transformer's pins, that means the SMPSU and horizontal output stage are one and the same.

    They can be a real pig to sort out - you need to work through the schematic and test any remotely likely suspects out of circuit before even thinking about taking readings powered up!
     
  14. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,747
    759
    No need for main chopper as the input is 115VAC.
    Just a bridge and series regulator to reduce the B+, probably.
     
  15. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,747
    759
    Need to know if the Stby is working or not.
    And a schema is very helpful with this TV as the TS is a n00b.
     
  16. ian field

    Distinguished Member

    Oct 27, 2012
    4,413
    782
    I'm pretty sure you'll find its a combined SMPSU/horizontal output.

    Its not so much what voltage a SMPSU puts out, as how stable that voltage is with mains variations.
     
  17. ian field

    Distinguished Member

    Oct 27, 2012
    4,413
    782
    Those standby transformers invariably have a thermal fuse bound under the tape insulation - failure of that isn't exactly rare, but the TS mentioned some symptoms of a TV in its death-throes, with a dead standby transformer it'd simply not start up, AFAIK: most sets would carry on working if that transformer died while the set was operating - it just wouldn't start next time.
     
  18. imraneesa

    Thread Starter Member

    Dec 18, 2014
    184
    4
    Here is the big image.
    http://tinypic.com/m/ipsehu/3
    http://tinypic.com/m/ipseib/3

    i am getting 110v ac on the primary of the transformer. and 9v dc secondary side after diodes.

    i am only getting 25v on big filter capacitor. and there is another small transformer. give me some ideas so i will test and let you know. snubber capacitor has some bulg on top it also.
     
  19. ian field

    Distinguished Member

    Oct 27, 2012
    4,413
    782
    The only other transformer I noticed is the small "jelly-mould" one which is probably the driver for the flyback transistor.

    The one right in the corner looks like the mains common mode choke.
     
  20. imraneesa

    Thread Starter Member

    Dec 18, 2014
    184
    4
    Yes that right side big transformer is getting AC current direct from the input. and it outputting 9V DC after diodes.
    What i am asking is why am i not getting 150vDC near filter capacitor? i am only getting 25V DC near big filter capacitor. if the capacitor internal resistance increase does voltage drop? is that big capacitor is the problem.

    i have studied all the risk and safety dealing with the television before i opened it. i bet my in-laws that with i can fix the TV. so i want to try my fullest best to prove that i can do that. so please help me guys.
     
Loading...