SMPS Repair

By on August 26, 2008

 smps repair

Recently one of my friend who work in the maintenance field sent me a switch mode power supply board for repair. This SMPS board comes with a control board for controlling display. The complain was no power and the fuse blown into a very dark color. There must be some components that had developed a direct short circuit that could have cause the fuse to turn into black and by replacing the fuse only will not solve the problem. My next step was actually to use a series light bulb trick but have decided to just scan from above to see if there is any visual indication of components blown. Scanning from above i could see the varistor have some problem. After taken out the part and check with ohmmeter and found that it was totally shorted.

 smps repairing

As usual one have to check for any corresponding parts first before you put back a new component and power On it. I have tested the bridge rectifier, power fet and check the big filter capacitor and components in the EMI filter circuit and found all of the components to be good. Conclusion, this switch mode power supply problem was caused by only a shorted varistor and a blown fuse. The indicators (LED’s) in the controller board  lit proof that the power supply was working fine upon power On.

 varistor

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208 Comments

  1. admin

    February 1, 2011 at 12:26 pm

    HI Bryan,

    Have you check the dc supply to the main power supply power ic? Certain power supply use optoisolator ic and the cpu will send a signal to the optoisolator ic in order to fully turn on the main power supply. If there is a missing signal or the cpu is bad then check the optoisolator ic area or replace the cpu.

    Jestine

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  2. Jay

    February 6, 2011 at 12:37 am

    Hi Jestine,
    In continuation to the previous post,I have checked bridge diodes which is there in primary section & those components seems to be fine and I have opened all other cap also. From the figure my problem is the 100ohm resistor before the bridge diode continues to burn even though I opened the secondary diodes. Ans my observation says the pin 5(drain) & 8(Source) shows shorted in the LNK304PN IC. Is this by design or the IC is blown. Also would like to know whether is there any chance of opto couplers be defective in any case. As a major components I have this power IC, 2 opto couplers and 2 FET's in secondary.

    Here is the datasheet of this IC and a sample diagram.

    http://www.2shared.com/document/SqwqLRc5/LNK304P.html
    http://www.2shared.com/photo/THz43RS9/SMPS_PowerIC.html

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  3. admin

    February 7, 2011 at 10:21 pm

    HI Jay,

    The drain and the source pin should not have a shorted or low ohm reading other wise it is shorted. Most likely the ic shorted that had caused the resistor to burn. As for the Optoisolator IC, yes it can be shorted.

    Jestine

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  4. Jay

    February 12, 2011 at 12:28 am

    Hi Jestine, Thanks for your valuable input. I have replaced the power IC and the 100 ohm resistor burning is stopped now. To my knowledge the primary is OK, but there is no output in secondary. I am confused whether this could be problem with the 2 opto-isolators or with secondary winding in transformer or with the 2 mosfets. Is the optoisolators related to secondary output switching by providing feedback to powerIC. Kindly suggest where I could start next.

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  5. admin

    February 12, 2011 at 5:35 am

    Hi Jay,

    Actually, any bad component either in primary or secondary side could cause no power symptom. Yes, if the optoisolator ic did not get any signal (feedback) from the secondary side then there will be no power.

    Jestine

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  6. vidya

    February 20, 2011 at 4:32 pm

    what is the work done by the optocoupler in computer smps & what is the main use of it.

    Likes(0)Dislikes(0)
  7. admin

    February 22, 2011 at 1:59 am

    HI Vidya,

    Try this link below:

    http://en.wikipedia.org/wiki/Opto-isolator

    Jestine

    Likes(0)Dislikes(0)
  8. gaurav

    March 15, 2011 at 5:40 am

    Respected sir,
    i want to learn smps repair please tell me about it

    Likes(0)Dislikes(0)
  9. shamsudheen

    March 15, 2011 at 8:19 am

    sir
    i want circuit diagrams of smps using transistor13007 and thats working thiory

    Likes(0)Dislikes(0)
  10. admin

    March 15, 2011 at 10:44 pm

    HI Gaurav,

    You can get my SMPS repair ebook at http://www.PowerSupplyRepairGuide.com or you can visit this link:

    http://www.repairfaq.org/sam/smpsfaq.htm

    Jestine

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  11. admin

    March 15, 2011 at 10:50 pm

    HI Shamsudeen,

    Sorry i do not carry any circuit diagram. I suggest that you search from this link:

    http://www.jestineyong.com/?cat=59

    Jestine

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  12. Nadeem

    April 7, 2011 at 5:36 am

    Dear Sir,

    I need your ebook " Testing of Electronic components" badly and trying to reach you for past three weeks. I do not have a credit card and can pay through WEstern Union bank ( 37 $ ). On receipt of amount you can provide the codes to download for the book and bonus books, thanks.

    Nadeem Sabir
    Jeddah, Saudi Arabia.

    Likes(0)Dislikes(0)
  13. admin

    April 7, 2011 at 6:11 am

    HI Nadeem,

    I have sent a private message to you.

    Jestine

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  14. Yaman Shrestha

    July 2, 2011 at 2:44 am

    Sir,
    I am from Nepal , I am a junior technician in this field , my problem was TV smps, all primary part are in the condition and STR also heating but no secondary out put what can i do please suggestion me

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  15. admin

    July 2, 2011 at 9:45 am

    Hi Yaman,

    Try replace the power ic and retest assuming you have check all the components in the primary side. Make sure also you check for bad diodes in the secondary side.

    Jestine

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  16. hafeez

    July 8, 2011 at 4:06 am

    Hi Jestine youg sir iam from india sir u r realy a great electronics engineer.I need your help i want to learn smps repair please tell me about it.
    Thank you sir
    your student
    Hafeez

    Likes(0)Dislikes(0)
  17. admin

    July 9, 2011 at 8:28 am

    Hi Hafeez,

    Get my ebook at http://www.PowerSupplyRepairGuide.com because it can help you to become a good repairer in tackling power supply problem.

    Jestine

    Likes(0)Dislikes(0)
  18. Gerald Factor

    July 17, 2011 at 11:10 am

    good day sir, varistor is usually connected parallel to ac line of smps? And sir what is the color black component in smps tv it has 3 pins,its look like a relay and connected to relay switch.

    Thanks and Godbless..

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  19. admin

    July 18, 2011 at 9:17 pm

    HI Gerald,

    Yes the varistor is connected parallel and the 3 pin black box component is a posistor for use in the degaussing circuit (to remove impurity in the crt colors)

    Jestine

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  20. Gerald Factor

    July 24, 2011 at 9:54 am

    Thanks for the info sir about the varistor and the posistor, how to check a posistor sir?

    Thanks and godbless.

    Likes(0)Dislikes(0)
  21. admin

    July 25, 2011 at 3:17 am

    HI Gerald,

    Posistor can't be checked and need to direct replace and retest.

    Jestine

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  22. harish kumar

    September 15, 2011 at 6:38 am

    I want to learn about smps pwm control ic 2005z

    Likes(0)Dislikes(0)
  23. admin

    September 15, 2011 at 6:59 am

    HI Harish,

    All PWM ic receive supply voltage and output a waveform. I suggest that you download the spec and read the datasheet as it has more information.

    Jestine

    Likes(0)Dislikes(0)
  24. Md. Shahjahan miah

    October 29, 2011 at 5:47 am

    I think, I will be benefited if I follow this documents.

    Likes(0)Dislikes(0)
  25. lee

    November 20, 2011 at 9:52 pm

    hi jestine,im repairing a smps ,on a venturer lcd tv,no power symptom,the problem is a 4 pin line filter on the ac side,which is sparking and now burnt out,is it possible to remove and bridge this for testing?everything else tests ok,just this problem line filter,the part number is lcl-1608wh other numbers on this part are 608980002050,hope you can help this has been on my bench for months now!!

    Likes(0)Dislikes(0)
  26. admin

    November 22, 2011 at 9:39 am

    Hi Lee,

    Yes you can bridge it with normal wire to test it out.

    Jestine

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  27. lee

    November 24, 2011 at 4:47 pm

    hi jestine ,further to the line filter i asked you about in last post,can i replace the line filter with another if it differs in specs?,or can i leave it bridged?,will it cause any concern?,thanx jestine

    Likes(0)Dislikes(0)
  28. admin

    November 25, 2011 at 11:58 am

    Hi lee,

    You can use another type or bridge it.

    Jestine

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  29. mahuvagara

    December 1, 2011 at 10:10 am

    jestin,

    I had purchase whirlpool white magic F65 Fully automatic washing machine . suddenly it is out of order, no power on no indicater.I had showed repaier of washing machine, he had simply asked to changed the circuit board. I am basiclly T V repaier. i had personlly checked circuit board, Find that Ac 230 volts comming but 12 volts dc is not generated. all diodes found ok one chip IC LNK304PM converter ic may be doubutful. please guide me if possible.supply its circuit diagrams if possible.It is fault of SMPS.

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  30. admin

    December 2, 2011 at 2:09 pm

    Hi Mahuvagara,

    I have not repair washing machine before but i believe all circuit board are quite common. In your case, did the power IC get the supply voltage? Sorry i do not keep any schematic diagram.

    Jestine

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  31. ranjith

    December 17, 2011 at 4:58 pm

    dear sir, i am a electronic student from srilanka. I would like to learn LCD and LED Tv repairing. Those tvs arrived srilanka before 1 year. After this year there will be so many sets out of warrenty. If you have a ebook on this please send me it. This will be a great help for me. Thank you so much.

    Likes(0)Dislikes(0)
  32. admin

    December 18, 2011 at 7:19 am

    Hi Ranjith,

    Try this link:

    http://www.electronicrepairguide.com/lcd-television-repair-ebook.html

    Jestine

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  33. Nagarajan

    December 25, 2011 at 7:10 am

    Dear Jestine Yong,

    I am a Computer Service Engineer and i run my own business since 1999. i always rely on other person to service my clients monitors and motherboards facing lot of problem due to delay and i am tired with triangular communication. Last week i googled about LCD monitor repair. there i got your blog it was fantastic. i registered with my email id and i received an article about repairing BENQ 17" monitor. i am surprised because i am looking for the same issue. Today i serviced this monitor by replacing C5705 Transistors and other suspicious Capacitor 1000Mfd 16V. Ha Ha it worked now i am typing this with my repaired monitor. Also i serviced Samsung 740 N 17" with backlight issue by replacing faulty Main Capacitor 100Mfd 450V with 100mfd 500V now it works perfectly (please advice if anything wrong replacing with higher voltage).you are awesome. you saved me lot of money as well as time(Time is Money). Thanks once again. please send the details what ever you have related desktop computers, Laptop LCD repair i am glad to purchase it.

    Nagarajan.K
    admin@ibeamit.in
    India

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  34. admin

    December 27, 2011 at 9:00 pm

    HI Nagarajan,

    Congratulation on your repair! It is ok to replace a slightly higher e-caps.

    Jestine

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  35. Sampat S. Pisal

    January 3, 2012 at 11:26 pm

    Very good,visual observations
    also makes man perfect in this field.

    Likes(0)Dislikes(0)
  36. Altaf

    January 17, 2012 at 10:23 pm

    Dear sir
    i have power supply of dell computer gx620, it has special fault when i turn on the power supply it happen on but not working and not taking load. please help
    thanks
    your student
    Altaf

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  37. Luciano F. T. Khware

    January 19, 2012 at 3:11 am

    Hi Mr. Jestine Yong,
    i am very happy with you sir. to say the truth i am learning alot from your articles that i receive every month. i feel blessed and enriched by your experience in electronics repair tips. i promise to be your faithful student.

    PROSPEROUS 2012!!!

    Best Regards,
    Luciano Francisco Thomas Khware

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  38. admin

    January 19, 2012 at 7:22 am

    Hi Luciano,

    You are welcome!

    Jestine

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  39. admin

    January 19, 2012 at 7:25 am

    HI Altaf,

    Do you mean the power supply can be turned on but shutdown under load? May i know what have you checked?

    Jestine

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  40. Mitch Aquino

    January 25, 2012 at 12:25 pm

    Hi Jestine,

    I’m trying to repair the SMPS of my 24″ LED TV. My suspect is the opto-isolator PC123, I’ve already bought a replacement but the only available in 4N35 (haven't installed it yet). Below are the symptoms my TV exhibits:

    At first power-up, it will work, then after 10 to 15 mins it will go on standby mode abdruptly. Upon powering it back up, sometimes it will come to life but will go on standby mode again after a few minutes. But most of the time it will not power-on, looks like it is stuck/locked in standby mode, even pulling the plug or setting it off for an 1/2 hour.

    This could be an opto-isolator problem? I’ve already checked the SMPS and it looks okay. I have voltages on the +12V, +5V, and in the +5Vsb. in the +12V rail, I do get +13V and one of the +5V rail has only +4.6V. Measuring the optocoupler, I have 1.1V accross the LED side and I think +2V on the photo transistor side.

    The PWM IC the TV uses is the MP1482DS, I haven't probe on this one yet, I just found out that it was sitting in the TV board and not in the PSU. I also suspect that some of my capacitors is a little bulged when using a flashlight (the bulge shines).

    Also as an added info there is a adjustable voltage regulator KA431AZ before/after the optocoupler, not sure on how to test it though.

    Your help would be appreciated greatly. This TV already testing my skills and know-how to the limit. Thanks.

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  41. admin

    January 29, 2012 at 5:05 pm

    HI Mitch,

    If the CPU and the eeprom have problem the power will go to standby also. I suggest that you directly replace the bulged e-cap and retest.

    The tl431 ic can't be tested with multimeter and you need to directly replace it and retest.

    Jestine

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  42. lee

    January 30, 2012 at 5:06 am

    hi there again jestine,im trying to repair a bush 32"lcd tv,the symptoms are no video,back lights are working and on,there is sound when connecting a input (ps3),there are no menus coming up on screen,i am suspecting the t con board,have tested the t con smd fuse and that is fine,ive come across what looks like another fuse (smd)on the t con, it has a marking of the letter"E" on it im not sure what this is?,it is white just like the fuse i tested earlier,when i tried testing on my dmm it went from 0.086 and kept climbing,also the outputs from the psu are fine all voltages are present,is there a way of testing the t con ?,im a little stumped on this one,many thanx jestine,lee

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  43. admin

    January 31, 2012 at 10:14 pm

    Hi Lee,

    No video and the sound/backlight is good most probably the problem is in either the t-con or the mainboard. Do you see any other "E" marking or just one? Make sure the t-con is getting the right supply voltage.

    Jestine

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  44. lee

    February 1, 2012 at 6:05 pm

    thanx for reply jestine,the smd with the "e"printed on it is the only one on the tcon board,the other that looks exactly the same is marked with"f" which is the fuse and has tested good,when you say check the voltage going to the t con board ,is that on the lvds cable from main board too the tcon?,i cant find any schematic for the t con ,so am not sure what the voltage should be going into the t con,if its any help the panel number is t315xwo1 v.2 and the t con board is 04a05-1e,and the tv is a bush lcd32tv022hd,i always thought if t con fuse is open then the display would be a bright white screen

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  45. lee

    February 1, 2012 at 6:22 pm

    ive tested all pin outputs from the lvds cable and the maximum voltage i get from any one of the pins are 5.0v dc

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  46. admin

    February 2, 2012 at 8:54 pm

    HI Lee,

    Yes you are right and the voltages should be 1.8v, 2.5 v, 3.3v or even 5 v. But then again it depends on the lcd tv model.

    Jestine

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  47. admin

    February 2, 2012 at 8:55 pm

    HI Lee,

    Try if the ICs in the t-con board getting lesser voltage than 5 volt. Afraid if any one of the voltage regulator ics will fail.

    Jestine

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  48. lee

    April 10, 2012 at 4:27 pm

    hi jestine ,can you tell me how to test a pwm ic?, part number (viper12a),this smps is not starting up ,its only got 5v standby,no other output voltages,ive tested mostly all of the components,mosfets ,capacitors,fuses,transformers,optocouplers,all tested good,the supply when plugged in is hissing " (2sec pause)hissing (2 sec pause) hissing etc etc,the voltage to the pwm chip is steady at 21v,on probing on the transister sides of the optocoupler im getting voltage going up and down,there is nearly 400v at the primary cap,dissconnecting the main board,and,inverter, jumpering the ps-on signal gives the same results,if the pwm ic was faulty would it not blow the mosfets?all these have tested good,helllllp!!

    Likes(0)Dislikes(0)
    • Jestine Yong

      April 11, 2012 at 12:38 am

      HI lee,

      To check pwm ic is to check the supply voltage and the output waveform. PWM IC faulty not necessary will cause problem to the fet. If it is direct short then only it will blow the fet. You also need to know that the shorted fet could also blow the power ic. In your case you need to connect to the original board to test it. Check the ps-on wire components because if there is any leaky component expecially the transistor could cause a no power symptom but still have 5 volt output.

      Jestine

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  49. lee

    April 11, 2012 at 11:24 am

    many thanks for you reply jestine,im right on it!,also i want to build a smps output tester which consists of 12v,24v,6v for testing the outputs on these supplys also with a built in current limiter as in the series light bulb trick,the 12v,24v,6v bulbs i will use, will be proberly be about 5 watts each,so will 5watts per bulb be ok as a load? ,there will be a  bulb on every voltage output pin of the smps ,and also a switch with a resistor to turn the ps-on signal on,all this will be contained in its own project box,and when finished i will be more than happy to supply you with pictures of the finished project,and how its made, for your website, to help others in the repair of these supplys,again many thanks jestine,always love reading your news letters you send me,i wish i had your knowledge !,lee.

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    • Jestine Yong

      April 12, 2012 at 11:50 pm

      HI lee,

      The wattage is depending on how big is the output ampere too. Yes you can use 5 watt as a test. Some use high wattage resistor as a load. Is this type of tester just for your type of power supply? If it is successful yes i need to put it into the website and let other ERG members to see. Check the website below to see if there is any help:

      http://www.soloelectronica.net/fuentes/Power%20Supply%20Repair.pdf

      http://www.repairfaq.org/sam/smpsfaq.htm

      Jestine

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  50. lee

    April 13, 2012 at 7:55 am

    it wont be for just one smps,it will be for multiple different suppys that need repairing,more like a self contained tester for testing the smps without the main board,inverters,t con board etc,(mostly lcd tv smps).

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    • Jestine Yong

      April 13, 2012 at 8:58 am

      HI Lee,

      Noted and all the best to you.

      Jestine

      Likes(0)Dislikes(0)

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