help with part please

Discussion in 'General Electronics Chat' started by sacha100, Oct 3, 2017.

  1. sacha100

    Thread Starter New Member

    Oct 3, 2017
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    Hi guys new to the forum so please be gentle,
    I have a Dell U3011t monitor which has a supply problem from what I can see, monitor switches on ok but after 5 mins it switches of and can not be turned back on without removing power and then powering back up of which the same thing happens again.

    I stripped down the outer casing and had a good look and tested voltages which shows the circuit to run at 30v, this is all good but as said after five mins circuit shuts down and voltage is lost.

    A bit more investigating and found one of the heat sinks getting very hot so put a fan blowing cold air over it and the monitor stays on, also there is a slight amount of heat generated burn around the transistor area so have removed the K10A60D Transistor nearest to the burning and have tested it and as far as I can see this is the problem.

    Anyway I am now looking for this part and am having problems because I am not 100% sure what it is called, also apart from the K100A60D marking there is another marking of 2:E of which I am not sure when ordering would make a difference or not.

    Any help would be much appreciated, also the best pace to order the part from
     
  2. ericgibbs

    Moderator

    Jan 29, 2010
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    hi100,
    This is the datasheet, you can buy these switchers.
    E
    What is your location?
     
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  3. ericgibbs

    Moderator

    Jan 29, 2010
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    hi 100,
    When you inspect the electrolytic capacitors located near the transistor are any of them showing signs of 'bulging' at the ends.??

    Failure of old electrolytic's is a common problem.
     
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  4. sacha100

    Thread Starter New Member

    Oct 3, 2017
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    Thanks for the info.

    I'm In Essex, England.

    So any Transistor with part number TK10A60D will do, I was not sure if the 2 had any reference at all. As you said E is for location would the number 2 be the same.

    I have tried the likes of maplin and RS components but they do not stock this item.

    Many Thanks once again
     
  5. sacha100

    Thread Starter New Member

    Oct 3, 2017
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    No bulging of any caps just a slight discoloration around the problem transistor
     
  6. ericgibbs

    Moderator

    Jan 29, 2010
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  7. sacha100

    Thread Starter New Member

    Oct 3, 2017
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  8. ericgibbs

    Moderator

    Jan 29, 2010
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    sacha100 likes this.
  9. sacha100

    Thread Starter New Member

    Oct 3, 2017
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  10. philba

    Active Member

    Aug 17, 2017
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    If it were me, I'd probably replace any nearby electrolytic caps. Might not make a difference but can't hurt and easier than opening it up again if it's a cap problem. Of course there is a risk of damaging the circuit board when removing any component that has to be considered... Kind of sad that modern electronic devices aren't designed with repairability in mind.
     
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  11. sacha100

    Thread Starter New Member

    Oct 3, 2017
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    Ok Guys still got problems with monitor switch off after 10 minuets or so.

    Changed out the two K10A60D Transistor which has made no difference what so ever, [​IMG]
    the heat sink is still getting hot to touch but from what I can tell now it is not the transistors causing the heat its an IC that is stuck under the heat-sink. [​IMG]

    I have tried to remove the heat-sink but without any luck as the IC is well and truly stuck to it. as you can see there is some kind of white mastic which is also attached to the side of what looks like a transformer.
    [​IMG]


    I have tested voltages, from what I can see is the voltage stabiliser/conditioner when unplugged from the rest of the circuit it is outputting 243 volts and when connected remains at 243 volts. from live to neutral and live to earth.
    [​IMG]

    Got a little shock when touching the hot heat-sink as my other hand was grounded on the monitors casing, did not think this should have happened so measured the voltages from the heat-sinks marked in red to the ground of the casing and it measures 131 volts all the others output 0. volts so nothing on them.
    [​IMG]

    Again I have had a good look all over the boards and from what I can tell there are no bad caps, no bulging or burning, the only slight marking to the board was around the K10A60D Transistor area off which I have changed out now.

    apart from removing and replacing components ( pot luck ) is there a way to start testing and ruling out comports which will lead me in the direction of the failed parts.

    I am a retired electrician so not to shy around voltages but have very basic knowledge when it comes to electronics so any help in pointing me in the right direction would be most welcomed.
     
  12. ericgibbs

    Moderator

    Jan 29, 2010
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    hi 100,
    As we suspected the most likely cause of the power supply failure of a switched mode power supply are the supporting caps.
    You could measure the ESR of each electrolytic cap, located close the K10 transistor, this means removing the caps.

    In the past for SMPS, I have found it easier and more effective to replace the 3 or 4 electrolytic caps, if you decide to go that route, get low ESR caps.

    As a very rough guide, run the defective SMPS until it shuts down, then ensure that the SMPS is unplugged from the mains.
    Pinch each cap in turn between finger and thumb, they should not be hot,,,, please take care.

    E
     
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  13. sacha100

    Thread Starter New Member

    Oct 3, 2017
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    Thanks for the info, the monitor I have is Dell U3011t LCD, the screen is good and has no problem running the LCD conditioning program with no dim areas.

    I can run the monitor without any problems with a small fan blowing over the IC chip that is covered by the heat-sink, but rather than doing this would like to find the cause of the problem and fix it,

    I have put a thermal gun over the caps and components and all are running around 25c that is all except the IC chip that runs around 40c then the monitor will shut down without a fan blowing over it.
    upload_2017-10-6_11-40-25.png

    I am still not convinced that I should be getting current of 131 volts from the heat-sinks marked in red to the ground casing. to me this is some kind of leakage.
    upload_2017-10-6_11-40-3.png


    Thanks again for all your help.
     
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