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What Voltages To Expect From The Secondary Output Of SMPS?

By on February 17, 2009


Is the secondary output voltages important? Yes definitely, in fact all these output voltages are the testing point to check how well is the SMPS. That means by just placing your test probe on those output pins you would know if the SMPS is working good, bad or have intermittent problem. The question now is what if you have not repair that type of SMPS before? What are the voltages you should expect? Its easy, just look at the working voltage of the filter capacitors. If the filter capacitor is rated as 1000uF 25 VOLT then you can expect the output voltage somewhere from 14 to 18 volts. If you get about 5 to 6 volts then you know the SMPS is not producing the right voltage. The marking on the filter capacitors is a very good indicator  of what output voltages that you should expect.

boost circuit

If you are repairing the Monitor SMPS, then surely you will know what output voltages to expect because CRT Monitors generally have a standard heater voltage which is 6.3 Volt DC. Not only that if you are checking the Boost circuit (that consist of B+ coil, B+ FET, B+ Diode, B+ Filter capacitor and current sense resistor) voltage line then you can expect about 45 to 50 VDC. If you get lesser than that say 25 volt, this clearly indicates the SMPS or the secondary side components that had caused the output to go low. This you have to troubleshoot and find it out with your troubleshooting skill.

Assuming you have not repair any Monitor (it can be other type of electronic equipment) before, what you need to do is to download the Monitor schematic diagrams and compares each of the SMPS output voltages so that you will roughly know what voltages a CRT Monitor can produce. Use this way to apply on other types of SMPS to locate the right output voltages.

Sometimes one have to spare some of their precious time to do their own research as with this way you will become independent faster than you can imagine. Without any sacrificial of your own time, you will only get slower result and this will overall affect your skill in electronic troubleshooting. Always think of a way that can help you to repair faster with accurate result either with the help of test equipments, coming out your own universal schematic diagram for a particular equipment or even from your own research and development (R & D). All the best to you!



  1. raja

    February 21, 2009 at 8:22 pm

    IT was very nice and helpful, awesome .

  2. admin

    February 21, 2009 at 10:01 pm

    You are welcome!


  3. teza

    May 13, 2009 at 3:06 pm

    smps circuiyschematic diagram 10a,20a, 12v, 12 in 220v out
    i want tis circuit detail diagram

  4. admin

    May 13, 2009 at 7:47 pm

    Hi Teza,

    Sorry i don't carry schematic diagrams.


  5. teza

    May 16, 2009 at 3:11 pm

    i want to testsmps circuit schematic diagram of 300watt interver can y help me .i very interst of your technology

  6. admin

    May 16, 2009 at 11:43 pm

    HI Teza,

    Sorry i do not carry inverter schematic diagram.


  7. leonard williams

    August 22, 2009 at 1:46 am

    i have 14 inch tv that i just cant get the smps to work i change the fet and up amp ic noting seems to work help me pleased thanks to you .

  8. leonard williams

    August 22, 2009 at 1:49 am

    hello jestin i would like to now how to arrive inthe factory setting menue of apex tv model#at 2002 thanks to you jestin.

  9. admin

    August 23, 2009 at 11:11 pm

    Hi Leonard,

    Sorry no information on that.


  10. admin

    August 23, 2009 at 11:12 pm

    Hi leonard,

    Have you check all the components in the power side? Is there any output voltage from the smps?



    September 30, 2009 at 5:30 pm


    I have a power supply on which it is indicated:
    Input:90V - 230V AC
    Output:12V 2A AC
    But when I chek the Output the numeric multimeter indicates 10.9V DC only.
    Tell me please, if the power supply is not good or i must put a load in the Output before cheking the Output voltage.
    Best regards

  12. admin

    September 30, 2009 at 7:46 pm

    Hi Nejib,

    12 V 2A DC or AC? If it is 12 volt 2 A dc and you got only 10.9vdc then it could be fault in the filter capacitor. It could also be no load problem. I guess you may need to open the power supply to lok for bad e-cap first.



    September 30, 2009 at 11:33 pm


    Think you for your answer I'm Sorry JESTINE it is indicated Output: 12V - 2A DC.

    best regards.


    October 6, 2009 at 2:23 am

    I have to think you about the advise that you gave me, about bad e-cap. It is really the case. I have to tell you that when I changed the first filter e-cap (470µF-16v) the voltage measured is 11.8 V dc and when I replaced the other one (1000µF-16v) the voltage became 12V dc. So think you very very very much for your help.

    Your faithfully

    Best reguards.

  15. admin

    October 6, 2009 at 7:56 pm

    HI Nejib,

    You are welcome!


  16. Damian Dubrocq

    June 10, 2010 at 12:31 pm

    Jestine: I have been years try to find a serious web site where you can download schematics from different manufactures of LCD monitors and never found, sometimes something very limited and more related to the schematics these people have already but not the one you need. I know from other people that are some web site that you pay (really not too much) and can get the schematics, list of comps etc, but I never find anyone who want to share with me these sites. Do you have something of these. Thank you for your attention, Regards, damian dubrocq.

  17. admin

    June 13, 2010 at 8:43 am

    HI Damian,

    Try this link:



    June 19, 2010 at 1:35 pm

    Nejib Hamouda again after about one year
    I have to say that you are a reference or a school that any one should refer to in any time...
    Please if you can help me: I have bought recently an SMPS I don't realy know what is it for. But on it, it is marked EPSON / AC ADAPTER /
    INPUT 220-240V AC 50-60Hz 0.25 A 22W
    The strange is that this SMPS has 3 Female pins:
    - one red wire:42V
    - one black wire: ground
    May question,if you can help me please, what the white wire is used for??? and If I chek with the multimeter the red & the black wire there is a slight tention.
    If you can help me please

  19. admin

    June 21, 2010 at 9:07 am

    Hi Nejib,

    I'm not sure about that wire in your type of power adapter. It could be a feedback from the on/off switch to trigger the power supply. You may need to check where the white is connected to.



    June 22, 2010 at 10:24 am

    Thank you for the attention that you have payed for my problem.
    After investigation the SMPS was for EPSON picturemate.
    An other information is marked on the cover of the SMPS for the third wire which is:CONTROL
    Can you tell me please if those information confirm your thoughts and how can i get 42v DC (+ and-) from that SMPS (how the smps can operate).
    thank you again and best regards.

  21. admin

    June 23, 2010 at 8:27 am

    HI Nejib,

    I believe the word "Control" to is trigger the power supply to turn on when the control wire is shorted to ground. I can't confirm on that because i do not have this complete system.


  22. Eric Smith

    June 2, 2011 at 10:50 pm

    Thanks Jestine this information will go a far way in helping me to repair SMPS

  23. admin

    June 3, 2011 at 4:45 am

    HI Eric,

    You are welcome!


  24. Pradip

    July 3, 2011 at 1:58 am

    we design 24V/3A SMPS,but Output Voltage is Vary from 22V to 28V so
    what can I do for regulate to this volatage at 24V exactly

  25. admin

    July 4, 2011 at 6:48 pm

    HI Pradip,

    Since I'm not a smps designer, thus i suggest that you either visit the designer forum or download many smps schematic and begin to analyze the circuit especially the circuit that have the feedback using optoisolator IC.


  26. nanhe

    July 22, 2012 at 8:10 am

    rispected sir 
     sorry for my poor english im from india i am reguler reed your electronics news  iam fesing a problum can you solve my problum i need  to change one indestreal crt moniter to lcd moniter but converter box(xvga box) not avalebal in india how can got it plese help
                                                                                                                                                   nandu (india) 

  27. nanhe

    July 22, 2012 at 8:29 am

    how can change any moniter oseletion friquncy 30k to 25k  with adde any component for use in fanuc cnc  
                                                                                                                                           nanhe (india)

    • Jestine Yong

      July 22, 2012 at 10:22 am

      Hi Nanhe,

      Sorry no info on this.


  28. Boyd Nyirenda

    January 30, 2020 at 3:47 pm

    Hi Jestine, I have a crt philip TV and after doing some troubleshooting, i found that there is only 1.4v from filter cap but with for rectifier diode on the same primary side the Ac voltage am getting 102v and no voltage on the secondary side of the board. What could be the problem?

    • Jestine Yong

      January 31, 2020 at 2:52 pm

      Hi Boyd,

      It could be caused by many factors, such as bad resistors, capacitors, fets, power IC, shorted primary winding and etc. I suggest that you read this link to get more repair ideas of power supplies.



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