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221K 2KV Cap Cracked In Power Supply

By on December 8, 2017
how to repair switch mode power supply











Received one desktop computer for repair; stating the problem symptom of no power.

atx power supply repair

I have checked computer by applying the power to the SMPS but there is no sign of life. I have removed the SMPS from the PC and opened it for the inspection. On visual inspection I did not found any physical damage or burnout signs.

So I took out my Multimeter and started “Cold testing” of the equipment. (Here term “Cold testing” is the process to check the equipment without applying the power i.e. resistance checking and “HOT Testing” is for testing the equipment by applying POWER and doing Voltage and Current testing.)

On cold testing I found Fuse is open circuit so I have removed the fuse this is 3.15Amp 203V ceramic fuse . And attached 100w Bulb in place of fuse to find out that only the fuse is blown? Or some other culprits are cause to blow the fuse by short circuit.

how to fix power supply

So for confirmation I have applied the power to the SMPS, and bulb steadily glow Bright that means some other culprits are there (shorted components.)

Note: On this symptom of bulb – advisable to instantly “put-off” the power or you can lead to damage more components on the PCB.

how to repair power supply

On applying power I found one high value capacitor suddenly omitting black fume so instantly I have switched off the power and started the process to find culprit.

I have removed the high value capacitor which has value marked  as 221K 1KV that is 220PF 1KV.

how to fix atx power supply

So I have again started cold testing on primary side to find what cause this part for failure. So i have start testing one by one surrounding components and I found one Zener diode shorted on PCB. I have taken out the Zener diode for the testing.

This Diode is 1N4734 5.6V 1W. I have removed this diode from the circuit because I have found one fusible .22 low Ω resister connected parallel with this diode and it may mislead you for finding shorted component.

how to fix and repair power supply

Now I have removed the low ohm resistor and again checked surrounding components seems ok. So replaced high value capacitor and zener diode

atx power supply fix

and by re attaching the 100W bulb I have turned on the SMPS this time Bulb light up bright for a moment and goes dim. That means there is no short circuit. For conformation I have checked voltage on Power on Green wire on connector side and I got 3V DC.

fixing power supply

That means SMPS is ready for running hence I have removed the multimeter probe from the connector and shorted green wire with black wire for starting the SMPS and instantly SMPS FAN started rotating that means now power supply is working. For my satisfaction I have tested voltages on the connector.

how to repair atx switch mode power supplies

After this test I have connected my SMPS Tester unit and see the result.

capacitor and zener diode bad

So finally I have replaced these culprits to get back this SMPS in working condition.

This article was prepared for you by Yogesh Panchal who works as a Computer Hardware Engineer in Mumbai India.

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Note: You can check his previous repair articles in the link below:




  1. Suranga Electronics

    December 8, 2017 at 7:15 pm

    Hello Mr.Yogesh .

    Well done..

    Nice Power supply Repair. and Most Popular Fault in power Unit.

    • Yogesh Panchal

      December 11, 2017 at 5:06 pm


      Thank you!

  2. Albert

    December 8, 2017 at 9:17 pm

    Good job Yogesh! These are the most satisfying repairs we engineers can do. Thanks for the well presented article.

    • Yogesh Panchal

      December 11, 2017 at 5:07 pm

      Thank you! Albert

  3. angelo

    December 9, 2017 at 6:39 am

    thank you sir
    i thought one more transistors or diode caused this issue
    keep it up

    • Yogesh Panchal

      December 11, 2017 at 5:08 pm

      Angelo ,
      I have checked surrounding components seems OK.

  4. Rajesh Narula

    December 9, 2017 at 8:21 am

    Good job Mr.Yogesh

    • Yogesh Panchal

      December 11, 2017 at 5:09 pm

      Thank you! Rajesh

  5. ramli

    December 9, 2017 at 12:31 pm

    good job sir...

    • Yogesh Panchal

      December 11, 2017 at 5:09 pm

      Thank you! Ramli

  6. Robert Calk

    December 9, 2017 at 2:12 pm

    Nice work, Yogesh. Thanks.

    • Yogesh Panchal

      December 11, 2017 at 5:10 pm

      Thank You! Sir.

  7. Mugabira Paul

    December 9, 2017 at 3:04 pm

    Good job Mr.Yogesh,
    Thanks for the well presented article.

    • Yogesh Panchal

      December 11, 2017 at 5:10 pm

      Thank You! Mugabira

  8. Henrique Jorge Guimarães Ulbeich

    December 10, 2017 at 5:45 am

    Very good, Mr. Yogesh.

    • Yogesh Panchal

      December 11, 2017 at 5:11 pm

      Thank you! Sir

    • Yogesh Panchal

      December 11, 2017 at 5:12 pm

      thank You! Henrique

  9. Samir edarous

    December 10, 2017 at 12:59 pm

    Hi Mr yogesh,good article thanks.

    • Yogesh Panchal

      December 11, 2017 at 5:12 pm

      Thank you! samir

  10. malamig

    December 11, 2017 at 7:06 am

    What is the purpose of a zener when there is a parallel fusible resistor?

  11. Yogesh Panchal

    December 11, 2017 at 5:36 pm


    Zener diode is used in Parallel with the load.
    It regulate and provide a constant output voltage to a load connected in parallel with it in spite of the ripples in the supply voltage.
    and resister is used for loading the current.

  12. Ulises Aguilar Pazzani

    December 12, 2017 at 11:56 am


  13. Geoffrey

    December 15, 2017 at 10:40 pm

    I enjoy the thoroughness and step-by-step walk through that you give in your article.  Makes for a good approach to adopt in troubleshooting. Thanks.

  14. Parasuraman S

    December 23, 2017 at 11:45 pm

    Good Job! Servicing SMPS is my craze!

  15. Muhammad Ashfaq

    February 15, 2018 at 12:42 pm

    ur fault finding is remarkable sir thanks .

  16. Francisco Rica

    February 1, 2019 at 1:38 am

    Good job Mr.Yogesh!! I have enjoyed much with your repair work and I have learn much!

  17. Marinko

    March 5, 2021 at 11:32 pm

    Thank you for the pictorial explanation in solving the problem.


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