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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202 Comments

  1. lee tucker

    April 30, 2012 at 5:10 am

    hi jestine,i was reading one of your articles about testing diodes that breakdown under a load,and that a analog meter is the best meter to test with,as long as the meter has a 12v output while in the times 10k and times 1k it will show up a leakage in the diode,my analog meter is a micronta fet,ive used my dmm to test the voltage coming out of the analog meter probes in the times 1k and times 10k settings ,and i get about 1.5 v,in this meter there is a 9v and a 1.5v battery in it,ive looked everywhere trying to find a analog meter that has the 12v output at the probes in the 10k and 1k settings but cant find one in the uk can you give a recomendation as to where i can get the right one? in diode setting on my dmm i get the 9v output at the probes !,but not the analog,thanx jestine,lee

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    • Jestine Yong

      April 30, 2012 at 9:05 pm

      Hi Lee,

      Try ebay:

      http://www.ebay.com/itm/New-Sunwa-YX-360TReB-19-Range-Analog-Multimeter-Continuity-/160671105426?pt=LH_DefaultDomain_0&hash=item2568be8192

      Jestine

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  2. lee tucker

    May 2, 2012 at 8:30 am

    thanx jestine,does that meter output the 12v at the probes in times 10?,looks like a nice meter

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    • Jestine Yong

      May 3, 2012 at 1:00 am

      Hi LEE,

      Yes at 10X KOHM it will output 12 volt.

      Jestine

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  3. mark sanders

    May 3, 2012 at 8:05 am

    hey there jestine,on that post above about the analog meter,how can that meter output 12v @10xk ohm when the meter only has 2 AA batterys in it at 1.5 volts each? just curious ,mark s.

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    • Jestine Yong

      May 3, 2012 at 9:53 pm

      Hi Mark,

      You have to make sure the meter has x10 k ohm range. If the meter has x10k ohm range this mean the meter internal is using 2 x 1.5aa battery and a piece of 9 volt battery.

      Jestine

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  4. mark sanders

    May 5, 2012 at 5:05 pm

    i understand now jestine,also how do you test a 4 pin optocoupler,i know how to test the led side,(reading in only one direction) but how do you test the photocell side??

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    • Jestine Yong

      May 5, 2012 at 10:36 pm

      Hi Mark,

      Check this out http://www.jestineyong.com/testing-optoisolator-pc123/

      Jestine

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  5. mark sanders

    May 9, 2012 at 4:43 pm

    hi jestine,can you show a way to test a 33167T 5 leg switching regulator ,and a kia78r09pi 4 leg low drop voltage regulator?,many thanx ,mark
     

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    • Jestine Yong

      May 11, 2012 at 12:55 am

      HI MARK,

      For any switching regulator ic, just check the supply voltage and measure the waveform of the output. You need a datasheet to do this. 78r09 has an additional pin. Check the datasheet and make sure the control pin have some voltage so that the output can be produced when there is a supply voltage to the input pin. The control pin act as a switch and usually the control signal is coming from MCU.

      Jestine

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  6. mark sanders

    May 11, 2012 at 6:43 am

    many thanx jestine,thing is im learning by removing most components to test them,im working on a samsung power supply at the moment,that just will not power up,standby voltage is there,when you press the remote power on the red light goes off,when you press the power on buttons on the tv,they are not ,responsive,all the caps test good on esr and capacitance,resistors all good,diodes test good,viper12a  pwm chip replaced ,also a F9222L 13 PIN CHIP,transformers tested good with my blue ring tester,all the transistors on heatsinks tested on my peak atlas dca meter have been recognised so assume no faults there,i can hear the pwm chip hiss then it clicks repeatedly every few seconds,but still no output voltages,ps-on voltage is there,voltages are up and down in sync with the pwm chip hiss and click,the psu is a BN44-00158A,http://monitor.espec.ws/files/158_109.jpg,REALLY STUMPED !

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    • Jestine Yong

      May 13, 2012 at 10:48 am

      HI Mark,

      Your case seems to be the standby problem. You may need to check if the CPU is getting the right supply voltage and make sure there is sinewave in the cpu crystal. When you press the remote or the on button the CPU has to output an on signal to the power side through optoisolator IC or a relay (through a driver transistor). If the CPU, relay or any component in the optoisolator circuit is bad then the primary power side will not be energized.

      Jestine

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  7. mark sanders

    May 11, 2012 at 6:46 am

    sorry link wrong here it is     http://monitor.espec.ws/files/158_109.jpg

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  8. mark sanders

    May 13, 2012 at 1:01 pm

    what other pins would i need to connect together to eliminate the power supply ?,i know the 5.3v needs to go to the ps-on pin,are there any others?ive included the pin configurations,thank you jestine

    connector 1,24 pin to main board:

    pin1,ps-on pin13,n/c
    pin2,5.2v pin14,gnd
    pin3,gnd pin15,gnd
    pin4,9.2v pin16,9.2v
    pin5,gnd pin17,gnd
    pin6,gnd pin18,gnd
    pin7,5.3v pin19,5.3v
    pin8,5.3v pin20,5.3v
    pin9,gnd pin21,gnd
    pin10,12v pin22,gnd
    pin11,12v pin23,12v
    pin12,n/c pin24,n/c

    connector 2 5pin to main board:

    pin1,det
    pin2,gnd
    pin3,pwm
    pin4,adim
    pin5,blu

    connector 3 14pin to inverter board:

    pin1,24v pin11,n/c
    pin2,24v pin12,b/L
    pin3,24v pin13,adim
    pin4,24v pin14,pwm
    pin5,24v
    pin6,gnd
    pin7,gnd
    pin8,gnd
    pin9,gnd
    pin10,gnd

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    • Jestine Yong

      May 16, 2012 at 2:45 am

      Hi Mark,

      From the pins result I can't make any conclusion unless I have the schematic. Since you mentioned that the PS-ON have voltage then try to trace where this line goes. I presume that it will end up in the optoisolator circuit. If the optoisolator circuit have bad component/s then the PS-ON signal can't turn on the photo transistor in the secondary side of the optoislolator ic. This in turn no full power will be output and the standby light remains red.

      Jestine

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  9. mark sanders

    May 16, 2012 at 7:52 am

    do you mean trace back the ps-on signal on the main board? and check components around there?,or on the psu?,when first plugged in the tv will have its red standby light on,when remote button is pressed to turn the tv on the red light will go off (samsungs do this apparantly ,normal),i used your trick with 2 analogue multi meters joined together to test optoisoltors and they give a reading only one way ,which is good.should the detect pin have voltage on it?,or does the main board supply that voltage when tv is turned on?.

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    • Jestine Yong

      May 21, 2012 at 8:55 am

      HI Mark,

      The CPU should send an on signal to the optocircuit (assuming if the CPU is good) and you could see some slight changes in voltage in the opto LED anode pin. Before that did the power IC in the main power supply getting any supply voltage?

      Jestine

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  10. mark

    May 22, 2012 at 8:07 am

    i removed the sheilding where i think the main cpu is,but it is one of those chips where you cant see any pins showing so i could test to see if there was voltage getting to the cpu,it is a chip where the tabs of the chip are underneath the chip,when you say the main power ic ,do you mean the 8 pin smd chip that is on the solder side of the psu?,the only other chip which is 8 pin is the pwm chip on the component side of the board ,(viper12a dip8) this one has been replaced, i think this chip deals with the standby section?

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    • Jestine Yong

      May 27, 2012 at 4:30 am

      Hi Mark,

      It depends on the design and yes some main power chips have it soldered from behind and it was a small 8 pins smd chip. You need to check the part number to double confirm. In other words the sub power supply has to function first and turn on the CPU before CPU sends out another signal to turn on the main power supply.

      Jestine

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  11. Raju

    August 11, 2012 at 9:13 pm

    Hi jestine
    When i reparing smps of the printer i found that mosfet shorted and also register also open 22 ohm that connected to drain the mosfer  then i changed the register and mosfet  after that  register heated and blow
    then i 1kv cermic capacitor on that line  i changed to 2kv cermic but again blow the mosfet and register
    please help sir

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    • Jestine Yong

      August 14, 2012 at 3:00 am

      Hi Raju,

      I suggest that you check all the components first before you replace and turn on the printer. Check if secondary side diodes shorted or not. Could you confirm if the resistor is 22 ohm or 0.22 ohm?

      Jestine

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  12. Salim

    September 14, 2012 at 5:25 am

    Hi Jestine
    I have a problem with a wii remote. Does not work. I did voltage testing from battery which is 3V. I continued testing and found voltage on smd resistor 3V. After the resistor the supply goes through a smd capacitor on the + line. On the one side of the cap the voltage reads 3V but on the other side of the cap the reading is OV. Does that mean the cap is open circuit? I checked the cap with multimeter and shows open circuit.
    Regards,
    Salim

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    • Jestine Yong

      September 14, 2012 at 9:32 pm

      Hi SALIM,

      If the cap is located in the supply line it suppose to work that way because the cap one pin is connected to vcc supply line and the other to ground. To check the cap you need digital capacitance meter and to check electrolytic capacitor you need ESR meter.

      Jestine

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  13. mubashir

    November 13, 2012 at 2:38 am

    Dear Jestine, Good day
     
    Sir I have posted couple of problems on this this website. During view pages I came to this page. I want to ask that how can I check smd capacitors on board with ESR meter. Kindly help me to repair this kind of circuits boards. Thanks
     
    Mubashir

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    • Jestine Yong

      November 13, 2012 at 7:32 pm

      Hi Mubashir,

      Just use the ESR meter and measure across the two pins of the SMD e-caps. If it is a non polar caps you need to remove and test it with a digital capacitance meter.

      Jestine

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  14. mubashir

    November 17, 2012 at 12:14 pm

    Dear Jestine,
     
    I am working on HP Compaq Evo D510 Power Supply. You can view this power supply on this link http://webdevsys.com/d510psu.htm. I think you have worked on it. In this power supply I checked on primary side where voltage on filter capacitor is ok. I check other components on primary side with oscilloscope. I got same wave form on both terminal of capacitors. There is no voltages on secondry side. Kindly help me.
     
    Mubashir

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    • Jestine Yong

      November 19, 2012 at 10:09 pm

      Hi Mubashir,

      I have not repair such model before but almost all computer power supplies are the same. In your case have you check all the components in the primary side? check also for shorted secondary diode. Make sure the power supply is connected to the original board. If this power supply is using power ic then have you check what is the supply voltage to the power ic?

      Jestine

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  15. koppula siva kishore

    November 22, 2012 at 2:06 am

    sir i have 11 frontech (750) ups in my office. iam changed the new battery but its not working connections all are fine ,its just oneyear old,  
    im checking so many times but its not working ,Kindly help me to repair this kind of ups"s . Thanks

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    • Jestine Yong

      November 24, 2012 at 9:52 am

      Hi Koppula,

      Sometimes it can be corrupted eeprom data that could cause not charging or charging led error.

      Jestine

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  16. mubashir

    November 24, 2012 at 3:30 am

    Dear Jestine, Good Day
     
    Sir I checked it and found that there some parts are missing. Sir without schematic how can I solve this issue. I don't have any other supply like it.  What to do ?
     
    Mubashir

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    • Jestine Yong

      November 24, 2012 at 9:51 am

      HI Mubashir,

      Without a schematic it would be very tough!

      Jestine

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  17. yaman

    December 18, 2012 at 3:29 am

    Hi jestine thanks for news leter and happy new year 2013 you too also ,
    I've one smps 12 output which is totaly parts (pre) damage and I replace all parts.after
    Replace all parts smps run well but output voltage is only 7.5 ,what the problem on ?

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    • Jestine Yong

      December 18, 2012 at 5:57 am

      HI Yaman,

      Have you direct replace the low ohm resistor (maybe 0.22 or even o.33 ohm). What about filter cap at the 12 volt-have you checked it?

      Jestine

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  18. Rad

    December 19, 2012 at 4:10 am

    Hi jestin , what is  the filter used for that connect across the smps tansformer  pri and sec GND, and if it is deffective what are the symptom?

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    • Jestine Yong

      December 21, 2012 at 7:56 am

      Hi Rad,

      For main isolation purpose. Some power supply will have no effect on the output. However to some, it could cause some minor disturbance in the output causing the monitor display to have some sort of small wavy lines across the display.

      Jestine

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  19. Rad

    December 21, 2012 at 9:25 pm

    Thank you again for the info.

    Likes(0)Dislikes(0)
  20. yaman

    December 25, 2012 at 5:41 am

    Hi Justine, in that smps only one resister fuse out it value is only 48 ohm and it replace wall, next one low ohm ( 8 ohm) used in opto. section it is not bad .

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    • Jestine Yong

      December 25, 2012 at 6:49 am

      HI Yaman,

      Sorry I don't get your question. Could you send some photos to jestineyong(at)electronicrepairguide.com (at) means @.

      Jestine

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  21. Charles

    April 1, 2014 at 9:47 am

    i have a question on SMPS repair, and it may seem elementary to most here but, here goes i have an old danika power supply and have no clue as to what the output is supposed to be danika went out of business years ago and i can not find a schematic online for this power supply so by looking at the components what is my output it has 32 pins

    thanks for your hard work and dedication to your craft Jestine

    Charles

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    • Jestine Yong

      April 1, 2014 at 7:34 pm

      HI Charles,

      I'm not sure what will be the output voltages. You need to test it with your dc voltmeter. I guess this could be a special type of power supply and not easy to locate the schematic.

      Jestine

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  22. Amir Mukhtar

    April 10, 2014 at 11:03 pm

    Sir Jestine Thanks you for your Sharing learning Articles.
    i do lot of learn and get knowledge about that.
    however, i have some problem in repair power Supplies.

    please guide me and refer easy way to clear mis-understandings with SMPS Repair.

    yours Student
    Amir Mukhtar Ashrafi

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  23. joy

    July 14, 2014 at 7:00 pm

    why desktop computer smps fuse and ntc damage ?

    Likes(0)Dislikes(0)
    • Jestine Yong

      July 14, 2014 at 9:13 pm

      Current surge.

      Jestine

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  24. Sam Medina

    November 27, 2014 at 5:30 am

    Hi, Jestine

    I´m trying to repair an ATX/2 PC SMPS that has a funny behaviour. when switched to 115 V or switched and conected to 230 V doesn´t turns on but if switched to 230V and conected to 115 V turns ON normally except that the outpit voltages are almost the half as U can expect conecting in a lower input voltage

    ¿any clue on what is happening?

    Many thanks in advance

    Likes(0)Dislikes(0)
    • admin

      November 30, 2014 at 9:20 pm

      HI Sam,

      If the power supply is switched to 115 volt with 230 v input, most of the time the components inside will blow but I guess this design could have the protection circuit preventing the components from blowing. If the power supply is running on a 230 volt but you only pump in 115 volt this means it received less voltage and full power can't be produced. To solve the problem just give what the power supply need. If it is a 230 volt power supply then supply 230 volt input.

      Jestine

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      • Sam Medina

        December 1, 2014 at 11:05 pm

        Thanks, but U don´t got the full picture, the problem is:

        switched to 115 V conected to 115 V = NO POWER UP

        switched to 230 V conected to 230 V = NO POWER UP

        switched to 230 V conected to 115 V = POWER UP, but voltages are roughly the half (12 V ~ 7 V, 5 V ~ 3V, etc)

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        • admin

          December 3, 2014 at 9:02 pm

          HI Sam,

          Although I have not come across such problem, I believe the problem could be an open resistor in the primary side that is nearby to the two big filter capacitors. Or try check all the components in that circuitry.

          Jestine

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          • Sam Medina

            December 4, 2014 at 3:06 am

            Many thanks,

            I noticed some silicon glue crystalized around the main filter caps, I removed all and for now the PSU is working normally I have it in test in my workbench, seems to be solved, once i finish testing will comment about to you,

            thanks again

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          • admin

            December 4, 2014 at 8:02 am

            Hi Sam,

            Decayed glue could cause problem to electronics circuit. Hope to hear good news from you.

            Jestine

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