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.
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.
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sekar
May 5, 2010 at 6:54 am
in 5v/40a smps output is come only 3v.how it rectify this problem
admin
May 5, 2010 at 8:33 am
HI Sekar,
Check all the filter e-caps for high ESR value with ESR meter.
Jestine
naresh fuke
May 9, 2010 at 6:18 am
respected sir
i have't ohammitter that time how will check my smps
please give me information.
admin
May 9, 2010 at 8:37 am
Hi naresh,
You need in meters in order to repair any electronics circuit which include SMPS.
Jestine
Bijay
May 10, 2010 at 2:39 am
I want to learn smps repairing, please tell me
admin
May 10, 2010 at 6:16 am
Hi Bijay,
Get my ebook on SMPS repair at http://www.PowerSupplyRepairGuide.com
as it contains lots of my SMPS repair secrets.
Jestine
Nirmal Mandal
May 10, 2010 at 10:51 am
Respected sir,
My computer power supply(model no:jil-2414D)is not working.Sutten the driver coil's(WYEE 16C) side condencer 1mfd/63volt is blust and now bord is short.please tell me about it with circuit diagram.
admin
May 11, 2010 at 10:20 am
HI Nirmal,
Sorry, i do not have the diagram. Just replace the components and checkk the corresponding components and retest.
Jestine
lawrence
July 2, 2010 at 9:50 am
Hi,
I salute you Mr.Jestine,thanks very much for the kind of information you have for who world. I want to request you to help me in getting one of your books because i having looking for it ,thanks
Lawrence (Kenya)
Rhodes Kufakunesu CHINYOKA
July 3, 2010 at 11:27 am
I did not know that there was such a wonderful and brilliant engineer like you sir.Thank you very much for your tips.Do you have repair manuals for specific brand of TVs particularly PHILIPS?What makes them continously blow the mosfet even after one has replaced a number of components with new ones?
admin
July 3, 2010 at 8:11 pm
HI Rhodes,
Thanks! Sorry i do not have schematic diagram and i guess you may need to search it from this link:
https://www.jestineyong.com/?cat=59
By the way, there are many reason why the mosfet blow. It could be due to shorted bridge rectifier, power ic, posistor, shorted primary winding of power transformer and even short circuit in the secondary side. I suggest that you check all the components above before putting a new mosfet and on.
Jestine
Rhodes K CHINYOKA
July 4, 2010 at 8:46 am
Thanks once again.Iam a polytechnic electronics and electronic comms tutor in ZIMBABWE.I hold the following qualifications:Advanced Technician DIPLOMA,Diploma and Certificate in Telecoms and Electronics (London-UK) ,a National Certificate in Electronic Serving(Radio and TV -Repairing).I would like to familiarise with new technology such as PLASMA .LCD TV and MONITORS.How much do your courses on these cost plus how long do they take to complete ?QUOTE in US Dollars
admin
July 5, 2010 at 6:06 am
HI Rhodes,
Nice to know about your achievement and thanks for your interest in the course but sorry we are no longer taking in international participants.
Jestine
murugan
July 8, 2010 at 2:38 pm
i have frontech smps (450w)
it is not working....
i want to fix it and
am thinking to use it as a regulated power supply,,,
pls help me 🙁
admin
July 8, 2010 at 8:00 pm
Hi Murugan,
I suggest that you open up the power supply to check the components in it. If the fuse blown then check all the primary side components especially the semiconductors. If it is okay may be you need to concentrate on the secondary side filter caps.
Jestine
Rhodes .K.CHINYOKA
July 11, 2010 at 3:50 am
Thank you Sir,My wish was to meet you and learn a lot about repairing and serving electronic equipment,unfortunately you are no longer taking in foreigners.My aim was to open a repairshop immediately after my return from your country.Anyway we shall always remain in touch .Thank you once again for the free tips you give to the world.You have become a global teacher .Pass my greetings to your family.
admin
July 12, 2010 at 4:27 am
HI Rhodes,
You can get my ebooks that comes with my support that can make you to become good in electronic repair. Thanks for the regards too.
Jestine
Rhodes Kufakunesu CHINYOKA
July 15, 2010 at 6:59 am
Sir
I take electronic eng students for workshop practice for 8 hours every week.Last week they were working on a SMPS of a Sharp DVD.A Zener diode on the secondary side was shorting.A thorough search for source of the problem has yielded nothing.I removed the shorted zener put a replacement and it became a short.I removed it .The DVD now functions normally with an open circuit.My fear is that the voltage is no longer regulated this might lead to more problem.What might the source of this short circuit?
admin
July 15, 2010 at 8:23 am
HI Rhodes,
First you must make sure the zener diode you replaced was the original value and next you need to check the surrounding components for bad components that had shorted the zener diode.
Jestine
jaygupta
July 17, 2010 at 5:03 am
hai sir i have a big problem in smps.
how to check smps and fault?
i want to good tips for smps.
pleas sir help me.
admin
July 17, 2010 at 7:40 am
Hi Jaygupta,
Please visit this website:
http://www.repairfaq.org/sam/smpsfaq.htm
Jestine
vinayak
July 19, 2010 at 12:53 am
moniter and sms capeciter check the multimeter book details .
capeciter and ic check the mutimeter deails ,
admin
July 19, 2010 at 4:33 am
HI Vinayak,
Could you elaborae because i don't get your meaning?
Jestine
Christopher Anderson
July 29, 2010 at 12:27 am
i have experince this problem alot but resently i get konka tv to repair with a varistor connecting with ser in circuit and measure near 0 ohm is that possible
admin
July 29, 2010 at 8:49 am
HI Christopher,
Sometimes repair tech can be confused between varistor and ntc. A ntc is connected in series and have low ohm while varistor usually is connected between the live to ground and neutral to ground. However, a shorted varistor can read zero ohm.
Jestine
Shyam
August 11, 2010 at 2:12 pm
Sir ,
i am from India, i having problem with SMPS
i Switched ON the Smps ,it suddenly busted and nothing went ON in my PC.I removed the Smps and checked it without connecting to PC . , nothing worked . I thought the fuse may have gone wrong so shorted it and then ONed th SMPS , again it s busted. what the problem what should i do ? hope u reply
admin
August 11, 2010 at 7:25 pm
Hi Shyam,
If the fuse blow again then there must be some semiconductors have shorted. I suggest that you check on the bridge rectifier and also the switching transistors for short circuit.
Jestine
CHINYOKA Kufakunesu Rhodes
August 18, 2010 at 7:26 am
Sir
Thank u very much for information on payment methods for the books.My family and I ve decided to open an electronic repairing technical school.We need your assist in area of training by sending a list apropriate textbooks you authored because we will selling some of them.
I aim to produce advanced skilled technicans hence the planning.
Sorry for replying late .I had to South Africa to do a practical test .Im studying towards a B.Tech in Telecoms(Electronics).
Im making arrangements to make a payment this August.
Greetings to your family and friends.God bless.
admin
August 18, 2010 at 8:02 am
HI Chinyoka,
I have replied to your email.
Jestine
kilevox
August 18, 2010 at 2:47 pm
Dear Jestine,
I am experiencing troubles with fixing SMPS of DVD player. I have located the problem (the MOSFET and zener diodes were shorted). Now while i replaced this components with new, the output voltage is too high - it reads 27VDC insted of 12VDC. Can this be problem in regulation (optocoupler and TL431), or elsewhere?
Best regards
Robert
admin
August 18, 2010 at 7:44 pm
Hi Robert,
Yes it can in that area. Check the surrounding for bad component especially the resistors and if all tested ok then directly replace the optoisolator and TL431 and retest.
Jestine
kilevox
August 19, 2010 at 12:43 pm
Hi Jestine,
I have tested surrounding for bad component - result was all ok, then i replaced optoisolator and TL431 - result is the same, still 27VDC on the output of 12VDC.
The other thing is, that there were absolutely NO marks on MOSFET transistor (typical so you can't repair the device). However i replaced bad MOSFET transistor first with IRF740 and further with P4NB80 - in both examples the output was 27VDC.
So can wrong MOSFET transistor cause this?
Best regards
Robert
admin
August 19, 2010 at 7:46 pm
Hi Robert,
Usually wrong substitution will cause the mosfet to run hot and blow. Try use K2645 and directly replace the power ic and retest.
Jestine
Manish
September 22, 2010 at 10:50 pm
Dear Sir, i want to check the smps to know that weather is it working or not. how should u suggest me..
admin
September 23, 2010 at 2:34 am
HI Manish,
Place the load and power on. If no output then the smps is not working.
It could be the fuse open circuit or other parts that have problem.
Jestine
Daniel F
September 23, 2010 at 6:06 pm
Hi Jestine,
I'm finding your website extremely useful and have already purchased one of your ebooks just the other day, LCD Repair. I am only novice to the electronics world, I usually work with computers and software.
I have an Acer 17" LCD Computer Monitor which had the 2 second to black fault. This particular model is well known for the e-caps failing on the secondary side. So I replaced a total of 7 e-caps with the same specification but better quality. The main filter cap tests okay using an esr and dmm.
Once I powered up the monitor instead of the 2 seconds to black I got a picture for 1 second then went black, then I got a picture for 1 second then black again and this cycle continued until I turned the monitor off.
So I assumed at this point that the PWM IC was cutting power because either the ccfl may be faulty or there is an over/under voltage.
Unfortunately, in the small time I had the monitor powered on, it seems to have damaged one of the n-channel mosfets which connect to the ccfl transformers on the inverter section. I have since replaced that bad mosfet and also a TL431 which I suspected of leaking, now I am back to the 1 second on, 1 second off cycle when powered on.
I would like to test the voltages on the PWM IC to determine if a over/under voltage exists but I am afraid that if I turn the monitor on again It will blow another component.
What would you recommend at this point?
Thank you, it is nice to find someone as polite and helpful on the www for a change.
Regards
Daniel F.
admin
September 24, 2010 at 10:12 pm
Hi Daniel,
The problem can be in the high voltage transformer dry joints or one of the lamp have problem. I do not suspect the power PWM IC because when the lamp have problem the feedback circuit will kick in and disable the waveform output from the high voltage transformer.
Jestine
basher
September 29, 2010 at 7:15 am
hi,i have hp workstation xw 6200 PC , but this PC not working , when i am connect power direct into smps its working good without shorting(green wire and black wire ), would u help , his this smps or PC problum
admin
September 29, 2010 at 7:44 pm
Hi Basher,
I'm not sure on that type of power supply whether need to short the pins or not. If you get the right output voltages then most probably the power supply is good. When you say the power not working, does it mean that when the power supply was connected to the board and not working and after removal from the board it was working? If yes then it could be the motherboard of the PC that have problem.
Jestine
sunny
November 19, 2010 at 12:47 pm
hello sir,i have a problem on lazerjet 8ooon smps,it was not powering at all so,when i checked on it one of the filter cap,was bad so i change the two capacitor.but it could not work.i have checked on transistors,diodes,bridge rectifier,though the I.Cs on the board i dont know how to read them if anyone is bad or not.so pls what next will i do?thanks
admin
November 20, 2010 at 5:13 am
HI Sunny,
If you have checked all the components in the power board then you may need to directly replace the power ic and retest. Usually for laserjet power IC spec is quite hard to get from the internet.
Jestine
Salman Sadiq
December 5, 2010 at 2:55 am
I am a repair technician, kindly help me time to time in giving me tips.
Thanks
Salman
Lincoln .O
December 5, 2010 at 7:57 am
Hi there! Yea, my DVD player was hanging. After ON/OFF it plays fine. Now, though, it's dead. No blown fuse but the 5volts output output is reading Zero?! Please, help.
admin
December 5, 2010 at 11:17 am
HI Lincoln,
I suggest that you check all the components in the power primary side. Make sure the secondary diode is not shorted. If all the components in the primary side is good then directly replace the power IC.
Jestine
admin
December 6, 2010 at 12:47 pm
HI Salman,
Please visit this link:
http://www.repairfaq.org/sam/smpsfaq.htm
Jestine
ilanthamizhan
December 10, 2010 at 6:20 am
i want to learn smps repair please tell me about it.
admin
December 14, 2010 at 9:12 am
HI Ilanthamizhan,
Get this ebook on power supply repair http://www.PowerSupplyRepairGuide.com
Jestine
Jay
January 27, 2011 at 1:09 pm
Hi Jestine,
I have a whirlpool whitemagic F65 washing machine. Suddenly it stopped with no power and I found that the 100 ohm resistor (fuse) is burnt. I have checked the bridge and seems to be normal as suggested in testing electronic components. Opened secondary winding diodes also, but 100 ohm seems to be continuing burn. To my understanding the IC LNK304PM pin5 and ground seems to have 0 ohms(shorted). But I can't conclude whether this is by design or the this IC is shorted.
kindly help and suggest the way forward to find where the short circuit occurs.
admin
January 28, 2011 at 9:49 am
Hi Jay,
Do you have the datasheet for the ic? I suggest that you trace along that burnt resistor circuit line. It could be semiconductor or other components have shorted.
Jestine
Bryan Simmons
January 30, 2011 at 6:51 am
hi mr. yong,
i am a level ii repair tech. in a military/medical electronics manufacturing company well seasoned in trouble-shooting very complex electronic assy.
I purchased both your lcd tv repair guide, and your smp repair guide. and might i say these books are outstanding!
i have a scott mod# lct37sh inch lcd tv with a MLT386X smp. that quit working. and when i checked out the supply it had a couple of blown smt caps in the primary circut, the fuse was blown and the inverter FET was shorted. i replaced these components, and now i get the 5v stanby voltage, but when i hit the power button the power led just blinks red a few times then goes back to standby dim red.
i have checked all the caps smt and through hole. they all test ok. i have checked all the through hole diodes and smt and they all check out fine. all resistors are within tolorance not sure about the smt caps though no way to tell what they are supposed to be with out the schematic. do you have any thoughts on what it could be that i'm missing? i can't seem to find any service manual or any support for this tv. i was wondering if you have run across these supply's in you daily trouble-shooting these seem to be a very common supply in a lot of lcd tv's and from what info i can find on these they have a bad overheating problem and burn them self's up. where should i look next? can't find a schematic of this supply anyplace it's made by megmeet any advice you could give me would be greatly appriciated
thank you for your time,
Bryan S.