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Sanyo Flat Shutting down

Discussion in 'Repairing Electronics' started by buddwisemonk, Oct 27, 2008.

  1. buddwisemonk

    buddwisemonk New Member

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    is it possible to test a rectifier with a standard meter?
     
  2. crutschow

    crutschow Well-Known Member Most Helpful Member

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    Smaller rectifiers (as would be in a TV) are typically axial lead, tubular type devices with a metal or plastic case. A Google for "axial diode picture" will show some.

    Some meters have a diode check mode (usually one of the resistance modes that has a diode symbol next to the settng). A normal diode will indicate some low resistance value in the forward direction (+ on anode) and an open circuit in the reverse direction.
     
  3. buddwisemonk

    buddwisemonk New Member

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    Sanyo Tech support says they got the part from Delta Corp and have no schematics. Tech support also says they don't provide any support for the board but would sell me a new board for $103 plus shipping =/ and of course my meter does not check rectifers like I had hoped. Beginning to become annoyed.
     
  4. dave

    Dave New Member

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  5. buddwisemonk

    buddwisemonk New Member

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    I tested for continuity on all the caps on the board and all of them seem to pass. not sure if that means they are good or not but there was one component that did not have continuity. There is a clear glass almost light bulb like component that I can get no continuity through. Any Idea on what it is or why it has no continuity? ....sorry if this is not of much help..doing the best I can here.

    There are 3 larger caps on the board..2 that are 820 UF and one that is 470uf. I replaced the 820's b/c they were bulging but not the 470.
    Well after no results with prior attempts I decided to test the voltage while TV is plugged in. Some of you are cringing i can tell. Well the 820's showed no reading but the 470 shows full read... Actually turning it on resulted in 820's showing read as well as the 470. Not sure if this helps but more info for you pros to use.
     
    Last edited: Nov 4, 2008
  6. buddwisemonk

    buddwisemonk New Member

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    still looking for any info you guys could provide and thank you for all your help thus far.
     
  7. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Like I said above, check all electrolytic capacitors in the PSU using an ESR meter, if you're using a multimeter you're not checking anything.

    There's also no guarantee that the fault is even on the PSU.
     
  8. flat5

    flat5 Member

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    Replace the 470uf. It may help. It's cheap and simple.
    The bulb thing might be an LED. Your meter will not test it directly.
    Have you Googled on the model number of the monitor.
    Sometimes you can find repair histories that way.
     
  9. cfbrooklyn

    cfbrooklyn New Member

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    Wow!

    Wow all you members know what your talking about! Great answers. I am going to need to brush up on my knowledge!
     
  10. Mickster

    Mickster Well-Known Member

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    Why? You got the TV for free and with the price of the caps you have replaced, you can't be out of pocket much more than a couple of $... :D

    What is the manufacter's name on the 470µf cap?

    If it's listed on the badcaps link I pointed you to previously in the thread, chances are it needs replacing too. Even if it isn't listed, it could still need replacing.

    How about posting a couple of quality photos of the board/section of board that contains your unknown component. Small/out of focus images are of no use.
     
  11. tonigau

    tonigau Member

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    Are you still trying to fix that screen buddwisemonk.

    Usually successful repairing of equipment needs technical competence (& experience) so expect to get frustrated.

    If the power supply on this set is a separate board then this helps to isolate faults.

    It helps to be able to identify different parts of the supply & the associated
    fault.
    If the screen just goes dark (but still sound from speakers) its likely the CCFL inverter section (for backlight).
    Weird behaivour or no start is most common the low voltage supply rail(s) fault & as advised is often overstressed Electrolytic caps.

    All the Elecrolytic caps on the output of the power supply that are filtering power should/must be LO-ESR for the power supply to operate stable.

    I source my Quality Electrolytic caps from RS or Farnell (Brand - type Rubicon YXF, Nichicon LXY, panasonic FC all have good ripple current spec) as the quantity I need is usually small.

    Part of a repair process should include supply rail checks before & after to help confirm the work but this could pose a danger if you are not experienced in working close to lethal voltage.
    I dont suggest you take any measurements with power applied !!

    The mains bus capacitor(s) don't need to be Lo esr (should be 105 deg C) & rarely require replacing.

    Look for overheated Board areas. This would indicate stressed parts (but not nessesarily failed)

    Also look for bad solder joins while you have the board out.

    As Mickster suggested attach a good photo or 2 & someone can Identify the caps that should be replaced or other parts you can check.

    Attached photo of power supply from a zerox LCD (with comments) just for info.
     

    Attached Files:

  12. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    May I just say, that's an appalling quality PSU, presumably out of a really cheap and nasty TV :D
     
  13. tonigau

    tonigau Member

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    Yep, cheap but typical. Its out of a Xerox 17" LCD monitor. The rest of the unit looks good quality though.

    Heres one from a Benq 17" LCD mon. The power supply is about 20% of the quality of the rest of the unit (this one has a LG/Phillips LCD Panel so its was worth fixing).
    Notice the heat stressed PCB, one of the output capacitors (C712) is almost on top of (opposite) to a SMD schottky diode surface mounted on the Solder side. No matter how good the quality of this cap is it will be seriously life affected from the heat.
    So its not always the capacitors fault, often I see life expired electrolytics that are pedigree but they are just over stressed (too miuch ripple current causes internal heating + heated from other parts.)

    Both these supplies needed Capacitors changing only, they were bulging/pressure relief open & leaking. (The HV input filter cap was fine, so were some others but replaced anyway)

    My advice to all is turn stuff off (at the wall) when its not being used, this way cheap stuff should last +3 years instead of 9 mths.
    Standby might be low pwr but the on time is large so it adds up.
     

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  14. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Among other things I repair Sony LCD TV's - I'm pleased to say that the quality of the PSU's is MUCH higher than those pictures. However, they do look pretty typical for all the cheap junk that's about - no wonder it doesn't last long :)

    I'm typing this using a 19 inch Digimate monitor, that I swapped for a satellite box - from cold it flashes the LED for a while before it comes on, then it's fine. I'm pretty sure it needs capacitors, but I can't be bothered to take the back off - perhaps when it gets worse?. Apart from that it's a really good monitor, and I'm very pleased with it.
     

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