Small Switch Mode Power Supply Repair Guide - Consumer Electronics SMPS How To Fix 

Glad to be of service Rob 🙂

Absolutely - I always get a high when I fix something and that feeling of achievement can be worth more than the item is 😀 True it also made a good educational video. If you liked this one (and didn't find it pointless) wait till you see tomorrow's repair! 😛

Just keep at it and you will find you start to recognize building blocks of a circuit rather than just a PCB

@@LearnElectronicsRepair Thank you

The reverse engineering thing is a skill you can learn. Just keep at it, learning electronics and how components/circuits work and you will get there I am sure. Reaching that point is something of an epiphany and this is where you should be aiming to be as your knowledge of electronics improves, When you get there I can guarantee to will get an amazing sense of achievement. Enjoy the ride on the way, Rich

@@LearnElectronicsRepair Thanks for your reply good Sir :)

Thanks for the info Pete - continually pressing the button to get the range you want is a bit of a pain

101% true - that is why I left it in rather than edit it out. It's a valuable lesson IMHO but also something you either develop for yourself or you just keep on getting zapped. No other way to describe it to anyone who doesn't already have it LOL

@@LearnElectronicsRepair Back in the 1980's I was working in a lab and got distracted and a few minutes later when I came back to the job inadvertently connected mains 240 v to the input of a 7805. Instantaneously there was a loud bang/crack and the body of the 7805 bounced off the ceiling and scattered cross the lab. The three pins were still in the board ! Of course I wasn't wearing safety glasses and if I had been looking over the board I could have lost an eye or worse. As they say, what doesn't kill you makes you stronger - or at least it frightens you enough to develop some sense of self preservation.😁 I would say to anyone getting into electronics - before you switch anything on just give it a once over in case you have done something stupid.

@@we-are-electric1445 Yeah I used to work for ICL back in the 80's in their Central Spares And Repairs workshop - with about 100 other engineers all doing component level repair. One of the product lines I worked on were large linear voltage regulators with banks of 2N3055 (or similar) type transistors on huge heat sinks and very large electrolytic capacitors the size of a Heinz Beans tin. This kit was already some years old and was built before switch mode PSUs were common. As was normal, there was a particular work bench for each product line and this one had huge linear transformers under it, some current trips (like 25A or 50A or something) and a socket where you could plug the board under test. I had been fixing these for a couple of days, then plugged one in and the current trips jumped out. I reset the trips and plugged it in again - they tripped out. So undeterred I threw the current trips to the on position and held them there..... the thing hummed like an electricity substation for a few seconds then one of the large electrolytics exploded with a very loud bang! As I sat there under this huge mushroom cloud with little bits of white paper like stuff raining down on me like confetti, the cheer that went up from the rest of the workshop was louder than the explosion! Of course it was all over the canteen and I got ribbed about it for a couple of days.... until...... There was another guy working on the high speed 'band printers' that could chuck out about 20 lines of computer paper a second (the paper was about 18 inches wide, had green and white lines on it, and sprocket holes down the sides and perforations so it neatly stacked itself into huge reams of paper). Anyway the 'band printer' had what can only be described as a large rubber band, wider than the paper, and fixed to it were all these lollipop stick type things. Each stick had one letter or number/symbol on the end of it (A-Z 0-9 repeated many times over and over again across the rubber band). Between the lollipop sticks and paper was an inked ribbon and in front of the lollipop sticks were these hammers (solenoids), one for each character position on one line of paper. So you can imagine how this worked, the rubber band rotated around two drive pulleys at high speed, the ribbon rotated on spools at a lower speed, and as the appropriate lollipop stick passed each hammer, it would hit it and print that letter. So basically after a short distance of travel, every possible character would be available for each hammer to strike once, and it had then printed an entire line of text, so it would then feed up the paper for the next line and continue. Now this thing screamed like a banshee when running so it had a big soundproofed cover over it. So one unfortunate guy was working on it and had some hard to find fault on a control board so he was probing around with his meter and had the screaming banshee running with the cover off (annoying everyone else) so he could take his measurements with the machine powered up. Anyway of course he slipped with the meter probe and shorted some pins on a logic chip. Suddenly there was this sound like a rail crash and thousands of lollipop sticks came flying out if this thing like a swarm of locusts on a biblical scale - some landing many meters away in every possible direction!! Well after that the banshee somehow realised it was dead and stopped moving and there was this sudden silence that fell across the workshop for about five seconds. Then we all did the only thing a self respecting engineer could do in that situation... everyone fell about the place crying with laughter and giving the unfortunate engineer more 'stick' than he had already had in his hair, clothing and god knows where else. It took about 30 mins for everything to clam down properly, and I had an easy time in the canteen after that as my little incident was clearly forgotten! The banshee incident would be raised in conversation every so often for years afterwards. Working at ICL were some of the best days of my life.

@@LearnElectronicsRepair Aye ! Those were the days. Every time I blew something up I was praying for someone else to have a bigger 'event' ASAP so mine would be forgotten. Trouble is, some of the 'events' pass into fokelore and get trotted back out at Christmas parties ! 😂😂😂😂😂😂😂😂😂😂

Also the glue they sometimes use to hold down the inductors or large capacitors (to help prevent them breaking away from the PCB due to vibration or physical shock) goes dark brown.black and becomes conductive. This is something else to look out for.

@@LearnElectronicsRepair Yamaha products often had this problem.

Hi Max. This isn't the easiest circuit to understand but you find it (or a version of it) in almost all switch mode power supplies so it is a very important one to get your head around. Let's try it again from the basics: The controller chip that drives the transformer needs power to work. This power supply voltage is called Vcc. When you first power up (and the power supply isn't running yet), the 1 Mega Ohm resistor connected to the 320V from the incoming mains supply, charges the little 10uF 25V capacitor - I made a video 'all you need to know about capacitors' if you need to learn about capacitors first. There is also a Zener diode which prevents the capacitor from over charging - again I made an 'all you need to know about zener diodes video' if you need a refresher course. *Capacitors* ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-R9slJUqT6Ls.html *Zener Diodes* ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-trjbHhLERic.html Once the 10uF 25V capacitor charges up to around 15 volts, the controller chip turns on and starts working, so the controller chip starts to draw power from the 10uF 25V capacitor. The controller chip then drives the switch mode power supply which starts running and you get output voltages on the secondary windings of the transformer. WHAT HAPPENS IF THERE IS A FAULT CONDITION If the power supply does not start after a short period of time (due to some fault) the controller chip stops running because the 1 Mega Ohm resistor can not supply enough current to keep the 10uF 25V capacitor charged and the controller chip running. Basically, the controller chip is drawing more power from the capacitor than the 1 mega ohm resistor can provide to recharge it, so the 10uF 25V capacitor gradually discharges and when the supply voltage drops to about 9V the controller chip switches off again and stops drawing current from the 10uF 25V capacitor. At this point the 10uF 25V capacitor starts to charge back up again via the 1 Mega Ohm resistor and when the supply voltage (Vcc) gets back up to 15V the controller chip switches on again. This property of switching on at one supply voltage (15V) then not switching back off until a lower supply voltage (9V) is called Hysteresis. The power supply will keep cycling on/off like this and often causes a chirping noise or you see the power supply LED pulsing on and off as long as the fault condition exists. . WHAT HAPPENS IF ALL IS OK If all is OK, the secondary on the high voltage side of the circuit (the one with the diode and two 100 ohm resistors) starts to generate voltage and this also charges the 10uF 25V capacitor. Now the capacitor has sufficient voltage supply (current) supply to stay fully charged and power the controller chip indefinitely, so the power supply keeps on working as long as you have it plugged into the mains. See if that helped you, then try that section of the video again: If it's still clear as mud let me know and I'll try to think of some other way to explain it. Once you master this part of the circuit you can repair just about any switch mode power supply.

@@LearnElectronicsRepair My goodness, and thank you so kindly for your reply - it’s truly appreciated. Yep, this is a LOT to wrap my head around, but I don’t give up easily. I will watch this video many more times, as I often do with your videos, because your approach seems so… natural, to me - I wish you were my uncle. And I won’t hesitate to ask more questions, you don’t have to worry on that front [I can be quite annoying]. Anyhoo, thank you so very much, for your help. Keep making videos, good sir. Cheers!

if i put the old knackered capacitors back in it powers up?? and mixer works apart from slight hum

It is actually a real Seasonic or a PC power & Cooling which at that time was getting their power supply from Seasonic ?, I have since 2009 about 18 PC power & Cooling PSU and some of them fail due to I gess aging electrolitic capacitors inside

Check in BIOS what the voltage readouts are - as long as they read above 12v, 5v and 3.3v then the psu is good for powering your PC, when under load some of these voltages can droop but if they get too low then there isnt enough voltage to power your PC, Seasonics are very good - doesnt suprise me its fine after 10 years if its been lightly used - the other thing to look for would be weird voltage spikes - like 5v spiking to 6.7v that could also be bad for the PC - what you want is nice stable voltages at say 12.3V, 5.1V and 3.34V

@@NOMADCREATIVESOLUTIONS Thanks for the info. I actually ran HW monitor and the lowest vdroop I got under load is 11.7 volts, spikes only to 12.4 the 5v is stable never goes under 5 and 3.3v is stable as well.

@@enriconapolitano4321 It's a Seasonic PSU bought alone, the model is SS-750JS.

11.7v is starting to get low but it probably will still power.. starts getting to 11.5v I'd maybe look at replacing it..

You shouldn't be able to find it yet. I always upload as unlisted until I complete any notes, chapters, thumbnail etc. It will be live very soon It never occurred to me it would appear on the playlist until it was public. Now I know, I wont add videos to playlists until they are ready 😉

@@LearnElectronicsRepair Probably the first time I’ve ever been the first view, first comment, and first thumbs up on any RU-vid video.😂😂😂 guess I was tossing and turning in the middle of the night and I’m always looking for new troubleshooting and electronics videos to listen to 😂 and as I think about the repair process while I’m listening… sometimes it distracts me enough so that I can drift back off to sleep.

Hehe no - but this is Gran Canaria and though it almost never rains in the south of the island (where I am) we get a lot of dust due to the Calimas which we get quite often www.lag-o-mar.com/lanzarote-hit-by-high-temperatures-what-is-a-calima/

@@LearnElectronicsRepair 😂 i know the island...( vacation ) But i was thinking more of the blue carpet pad and the power supplies

@@allinclusive5762 Hmmmmm.... Maybe I should get the wife to clean my workbench 😅

@@LearnElectronicsRepair That was my thought! 😉👍

Are you referring to the power supply in this particular example, or in switching power supplies in general? In my particular experience of dealing with many different varieties of power supplies, the primary failure is one of the switching components, either mosfets used for the actual power supply switching, or the PFC(power factor correction) mosfets or a combination of those with the driver ICs and coupling components for the mosfet switches. Only about 10% of the time do I see the bridge/main rectifiers go. And, if they do go, it's usually because something upstream already failed. The typical PSU failures are mostly the cause of some kind of abnormal stimulus to the PSU, such as a high temperature/inadequate cooling, a dead short on the output from something external to what the supply is driving, or at the end of life for the electrolytic caps and their leaking or exploding. Your comment is certainly an easy very fast first check with a continuity meter but also, while in diode check, quickly one can go for all the mosfets and switching diodes. But the rectifiers are certainly not 99% of the time with switching PSUs in general, believe me, I'd love for them all to be so easy to fix and have some nice quick checklist to get these things fixed fast. But it's not so easy many times with more complicated designs especially with ones using unusual and weird switching ICs without available datasheets and schematics.

There's 2 of them with domed tops at the edge of the board. They're obvious as soon as the lid is off.

@@1magnit Isn't that exactly what I showed at 04:25, immediately after explaining the *MOST* important thing first - which is to check the main (bulk) capacitor does not have a dangerous high voltage charge in it before looking for anything else?

@@LearnElectronicsRepair Sorry, I was skipping parts of it. Just look for the obvious first before getting out the meter. Often with those things there's a power transistor mounted on a heat sink and one of the small coupling capacitors is right next to it. Those dry out but they don't get a bulge in the top so test them in circuit with the ESR box. It's pretty much ALWAYS a capacitor that's failed in those things