Did you test that poly mains class x cap ? It got a kick when the diodes and fuse went. Is it interfering with the power to the small controller chip ? Thanks for the interesting, deep dives 😉
@@jdaraireland I didn't John. I did check the start up capacitor on the SMPS controller (After the 2x 750K resistors) but I only did it in circuit with the capacitance meter, it's reading 9.9uF so it looks good. I will be revisiting this one and the two others I did not already look at in a part 3 after some parts arrive which is likely to be a few weeks so we will all find out more then 😁
I really enjoy watching these videos on SMPSs. It’s great that you go thru the details, over and over for each video, as that works so well for clarity. Thx.
I am SO glad to see this video. I have been waiting for part 2, ever since part 1. I never thought you would post it in the middle of the night, but thanks. I really appreciate your videos, and am hoping you will tackle some bench power supplies. Keep up the good work.
Haha It was published at 8:30am Sunday Morning here, just before I went to the car boot sale. I had to leave it overnight as UA-cam was still checking for restrictions. Actually I started uploaded the 24 hours video earlier on Saturday morning, which took a couple hours, but when I went bed about midnight it was still processing so I gave up waiting. Yeah I would like to get my hands on some faulty bench PSU to repair.
These videos are gold. I have a laptop power supply that died, so opened it up and found the main fuse blown, along with the high voltage mosfet shorted and the sense resistor open. Replaced the components along with all electrolytic's but no joy, then went looking for shorts but found nothing. Its a toshiba power supply, the driver chip is unobtainable and with no simple way to test it, I put it aside until I could be motivated having another go tracking down the fault. Will definitely watch part 3 if you make it.
Thanks Richard for parts 1 and 2, looking forward for part 3. I have watched many videos on SMPS , but yours is the one that gets down to earth (no pun intended) on repairing them. Not only good explanations but also practical demonstration too. My background was linear psu's and I was shy of starting hands on repair of SMPS, but now I feel much more confident in giving them a real go. Thanks again.
Every time I expect you to say it isn't cost effective and give up I'm thrilled to see you keep trying to fix it. Thank you for sharing your expertise and I can't wait for the next part.
Sometimes I fix stuff just for the satisfaction of it and expanding my own horizons. That's kinda how I got to here - keep on trying to fix some stuff and by doing so learn how to do it much quicker next time. 🙂 This is what I will say to anyone who wants to learn electronics repair - try to fix as much stuff as you can get your hands on, even if it costs more to fix than it is worth, and even if you can't fix it in the end, you can't put a price on the experience you gain in the attempt.
Thanks to your videos, I've managed to repair (and also understand a little better) a 230v to 12v SMPS for a Heat/Cool Box. Your explaining and commentary feels very natural and easy-going which makes it much more interesting, than watching a video where it feels like someone's just reads from a script. Keep up the good work!
Excellent, Richard.. thanks very much for part 2. Would be interested to see those last two if you wish to do so. Also, to see when you replace those smd pwm chips.
Hi Rich following your videos and really enjoying them. I too am a fellow clayhead. from the posh end. ( sneyd green ) . i too played with electronics in the early 1970s. but lost interest but now i'm retired have started to take an interest again. learning all the things i should have learned back then. I would love to see you get those power supplies going with the new chips you ordered. and tackle the ones you ran out of time on. Loved the nostalgic bit about shorting your train transformer out with your BUGGERS . I think your explanations are very easy to understand you must have spent months in a classroom learning all this to give us a simple abridged version. My interest was rekindled by a fruit machine psu i volunteered to repair everything works except the 44 volt output for the lamps. on power up it works then after 10 seconds or so the voltage drops away slowly down to a couple of volts having watched and understood your psu videos i reckon it's probably the feedback circuit or the chip feed capacitor gone proper leaky once warmed up. i've yet to test it. but i feel confident now i can diagnose the problem. Would love to know where in the potteries you lived. I'm watching your component explanations too. Nice and easy to understand. Best Wishes Paul Dickinson
Thanks Richard for all your hard work and sharing knowledge, I have picked up a lot of tips from watching you and another video would be appreciated...Greetings from New Zealand
Excellent, Richard.. thanks very much for part 2. Would be interested to see those last two if you wish to do so. Also, to see when you replace those smd pwm chips. Bravo, sir!
You are AWESOME Richard! Thank you, thank you, thank you! So enlightening and so passionate that I literally can’t stop watching your videos and sometimes even more than one time. Keep up the great content!
Very interesting. The procedure for finding faults brought me a lot for these switching power supplies. A little more editing or using time lapses (for the soldering and desoldering parts) would help reduce the length of your videos. 2:24 for this one! To check if the other viewers are more or less of my opinion. Keep up this exciting work!
I guess then some others would say 'but you don't show the desoldering and soldering techniques properly, and I'm trying to learn how to do it' 😉 I'm glad you liked it though, I think we can all agree there is very little 'filler' in the videos. I think putting chapters into the long tutorials is a good compromise, but then sometimes I deliberately don't do that and sometimes even say at the start 'spend the time to watch this through and you will learn some stuff, skip parts of it and you won't' LOL
Wow the Pet Shop Boys, a real blast from the past, enjoy the concert Rich. I wonder if they will mime or actually sing. Let us know what you find out when you go see them. Unfortunately some of the old bands don't sound anything like they did when they were in the charts. Some still sound fantastic.
Noting that at 1:16:43 when you are measuring the from the mosfet gate to the chip, the resistor you are going across is a 000 ohm resistor/ jumper so shouldn't have been interfering with the reading on a continuity test. That would suggest perhaps that jumper has a higher resistance than it normally should?
hi Richard, enjoyed the video. I especially liked the idea of injecting 5v into the secondary side of the power supply to stabilise the feedback circuit. What do you think to this idea? Remove the Optocoupler and replace with a diode on the primary side then measure the voltage across the capacitor near the Octocoupler and if the voltage is not stable the fault is in the primary side, if it is stable the fault is in the secondary side, any components that are shorted on the secondary side will now begin to heat up because the primary side is fully on, then use your thermal imaging camera to find the shorter component in the secondary side. Hope you enjoy the concert with the Pet Shop Boys they make some really good songs, love them when I was a kid, but I was into the group madness and I think they're in their 70s now. time flies two fast.
@@LearnElectronicsRepair sorry Richard should have been a bit more descriptive I was thinking more in line with an ATX power supply with multiple Schottky diodes on heatsinks on the secondary side. It was not my idea, I saw it on another UA-cam video. thought I'd share it with you because I thought it was a good idea 🙂
If you externally drive the output voltage above the normal regulation point you will drive the duty cycle of the converter to zero which means the output of the winding which powers the control circuit will produce no output. The circuit will then rely entirely on the start-up circuit. It will therefore try to start, fail, delay, try to start again and cycle forever in failure. It isn't really common but some controller ICs, especially those with an integrated switch, will shut down if they detect excessive voltage on the switch. This can happen if the network (R, D & C) that snubs the leakage inductance spike has failed. The resistor in these snubbers often runs quite hot and may fail. The fact that the circuit (#5 ?) worked when warmed very strongly suggests to me a flaky solder joint somewhere. There is a small chance that shift in the current transfer ratio of the optocoupler may be at play.
Thanks a lot again for your fascinating tutorials. I hope you'd decide to fix more of them (like part 3 or something) for us. That'd be hell of a huge help:) Thanks in advance
The tube has its share of repair people who magically unsolder anything in one second top, and own 10 boutique irons that instantly melt any solder, specialized tips and all, never having any trouble thanks to the power of video editing. It's refreshing to see somebody doing real work, struggling to cut heatshrink open or fighting with a soldering blob. Repairing stuff is a rewarding but often painful, frustrating, long and tedious task. Your workbench somehow resembles mine. And things get disconnected, pieces wobble at just the worst moment, you never have enough fingers, the right tool is off or to the other side of the lab and you resort to undo screws with pliers and stuff :D That's my kind of workflow. Of course, your experience and knowledge are on a different level, and I'm learning a lot. Thank you!
Does the usb-c power delivery change the basic structure of the output side? Do they require something else than an additional chip for handshake? Thanks for the superior series! It has taught me a lot more than electrician school in 3 years.
Looking forward to part three. When the scope showed that the transformer wasn't powering up, what would you have concluded if it had been powering up? I have a USB charger that is pulsing 4V@1Hz on the output, so I'm wondering if the PWM is not getting its second source to VCC, and the startup circuit charges the capacitor enough to run for only a second.
Thanks Rob, I found a few more descriptions giving page not found error on the patreon link- it seems like the error crept in somehow on one of the videos in the PSU playlist a little while ago. I generally use the UA-cam option to reuse the details from a previous video (in the same playlist category) and then edit the description to suit the new video, so I must have reproduced the same error. I think I found them all now. Cheers. If anyone would like to help support this channel you can subscribe at Patreon on this link and select your donation amount www.patreon.com/learnelectronicsrepair Thank you
Your videos are amazing, you explain everything simply. I really do understand transformer’s a lot more. Richard how does a toroidal transformer differ?
Heya, 1 more good vid learned some more so that is great thanks. I'm going to make a empty bedroom into my elektronic repair hobby room to see if your explanation ( and my 30 years ago electronic school learning) are good to start repairs myself. I told a colleague of my about this and he brought me a psu like the 1 you show in 1 of your vlogs it is the 1500 W psu only this 1 is 1200W pritty simialer. I have a youtube channel is I'm gone film it and afterwards gone upload it if you like I can sent U a link wen I have uplooad it.
Hi Richard, very interested to see your method of testing the feedback circuit. I'm gonna try this. I have seen another version online (from Haseeb Electronics) where he puts a diode across the primary side pins of the optocoupler, which allows him to test for issues with the feedback circuit.
Excellent advice as usual Dicky, thank you for sharing this information on the black art of PSU's, it really helped me to understand how they work. Please can you show the control chips repair if you can, would be nice to see the last 2 fixed 👍🏻 😁
Yes, I've ordered the parts and I will review this with a part 3 when they arrive but they will take a month or more from China, then I will look at the other two. I also have one more repair technique up my sleeve for a part three.
@@LearnElectronicsRepair that's great to hear your going to finish off the repairs, and now reading you are going to show another technique is even better, that trick you showed putting voltage on the output blowed my mind, I would never of thought of doing this but yet it made perfect sense when you explained it yeah 👍🏻 😁
Well in the first PSU you check the driver pin goes to the resistor and the other ebnd of the resistor goes to gate, but you did not notice that the resistor is zero ohm and meter didnt show that. It is possible that the first failure broke the 0 ohm resistor to the gate, the resistance drops down when parts are heated that can explain why it stabilizes () maybe even resistor on the gate drops the resistance when heated. Can you do follow up with check if chagne that 0 ohm resistor will not resolve the issue?
Richard, can you please explain a bit more about the +vcc supply to the PWM which comes from one of the secondaries of the switching transformer? As these voltages are galvanically isolated what reference voltage is being used to provide a potential difference to feed the chip? I assume hot ground but would like a refresher on how it works, my electronics theory is very rusty (I stopped working as an electronics engineer in 1992! Love the videos BTW. Thanks, Dave
Dave Adams Technically speaking the secondary that provides the Vcc to the PWM chip is galvanically isolated from the primary but one end of the winding is then connected to hot ground so that effectively defeats the isolation. As the PWM chip is on the hot side of the PSU the Vcc supply does not require isolation, but it does need to be referenced to hot ground, same as the PWM chip itself is. One may think you could use a tap on the primary winding, like an auto-transformer to supply Vcc, but this is not the case as neither end of the primary connect to hot ground. So we are not really using the secondary to take advantage of the galvanic isolation, we are doing it that way so we can efficiently create a low voltage (usually 15V) Vcc supply AND reference it to (hot) ground. Usually there is no regulation on Vcc (apart from that provided 'second hand' by the regulation of the output voltage) but sometimes there is a zener diode from Vcc to ground as I mentioned in the video.
Nice teaching, the feedback circuit testing method is really amazing but i think it works only with a psu that has one output voltage, what about a psu that has two or more output voltages, i have two psu one with 5v and 12v output and the other one with different output voltages 3.3v 5v 12v 24v i've tried to inject voltage a bit higher for each output but nothing shows up on the dmm on diode mode across the optocoupler collecror to emitter pins. Thank you
That water wheel analogy is just bizarre, especially that weird bypass circuit. It completely fails to illustrate the most fundamental operation of a flyback converter. The energy stored by the flywheel effect is, when the valve is closed, delivered to something totally lacking in the diagram - the output circuit. When the switch turns off the vast majority of the energy stored in the inductor (so-called "transformer") is delivered to the secondary circuit. Ampere-turns are conserved. If the charge winding ('primary") has 100 turns and a peak current of 1 ampere at the instant the switch turns off and discharge winding ("secondary") has 10 turns, its current at the instant the switch turns off will be 10 amperes. That current ramps down linearly with time, all the way to zero in most flyback converter designs ("discontinuous current mode") though not in all designs. If it _does_ go to zero, the current in the charge winding and FET starts at zero and ramps up linearly with time. The diode in the output circuit prevents any current from flowing simultaneously in the charge and discharge windings. The purpose of the snubber is to discharge "leakage inductance." Leakage inductance is modeled as a small inductance in series with the primary winding . It has no magnetic coupling to anything but itself. It is the result of imperfect magnetic coupling between the charge and discharge windings. A little bit of energy is stored in the leakage inductance when the switch is on but it can't put that energy into the discharge/secondary circuit. The leakage inductance causes a very narrow but high voltage spike as the switch (FET) turns off. The spike energy is dumped into the snubber capacitor via the diode. The resistors then discharge the cap in preparation for the next cycle. The diode is usually an ultrafast recovery type, though if the circuit is done carefully an ordinary diode can be used and the reverse recovery energy actually helps to discharge the capacitor when the switch turns on, reducing the amount of energy that has to be dissipated by the resistors across the cap. In fact with discrete FETs the avalanche energy rating of the intrinsic body diode may be adequate to handle the energy from the leakage inductance. The capacitor value is fairly critical.
I have found that in some instances of an unstable output the main bulk cap would be bad. This and failed switching transistors seems to be the most common things in those cheap SMPS modules from China that you can buy off ebay as LED lighting power supplies. I can repair these things or better yet out of the box "upgrade" them with better transistors and caps, though I do have a youtube channel I am not good at presentation and explanation of what I am doing and why. I have a few videos on communications related electronics and some video gam related stuff but they are nothing to write home about. My thinking is maybe a video covering those SMPU modules that are rated over 10 amps and of 5 and 12 volts types since there are plenty of videos on 24 volt 10 amp versions out there. Reason I mention over 10 amps is because the actual design of the SMPU changes physically.
Nahh it will just stop the resistor from blowing again LOL. It's not like it is supposed to be a fuse and a lot of current can't really flow that way due to the 3x 180K resistors in parallel. Actually I'm a bit surprised the 0R went open at all - or the blown up track. Looks like some sort of liquid got into the PSU if you ask me, but there is nothing around there for liquid to short to
Interesting UA-cam videos like this one are a form of software since you make it once and every view counts as revenue. That is the economic explanation and that is why you will find lots of videos in UA-cam that don’t make sense but they do through the UA-cam lens.
I like the ol' e SWASTICKA looking resistor at the beggining AUSSIE AUSSIE AUSSIE!!!!@!........ OE,OE ,OE.....😅😅😅😮😢😂😀🫠😃😄😁😅😅🤣😂😂😂😂😅😆😁😉😉😉😉😉😉😉😉😉😉😉😉, JUST KIDDING MAN.....😢😢??
NOTE:
The Diode D5 at 02:02:07 tested OK
Did you test that poly mains class x cap ?
It got a kick when the diodes and fuse went.
Is it interfering with the power to the small controller chip ?
Thanks for the interesting, deep dives 😉
@@jdaraireland I didn't John. I did check the start up capacitor on the SMPS controller (After the 2x 750K resistors) but I only did it in circuit with the capacitance meter, it's reading 9.9uF so it looks good. I will be revisiting this one and the two others I did not already look at in a part 3 after some parts arrive which is likely to be a few weeks so we will all find out more then 😁
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I really enjoy watching these videos on SMPSs. It’s great that you go thru the details, over and over for each video, as that works so well for clarity. Thx.
I am SO glad to see this video. I have been waiting for part 2, ever since part 1. I never thought you would post it in the middle of the night, but thanks. I really appreciate your videos, and am hoping you will tackle some bench power supplies. Keep up the good work.
Haha It was published at 8:30am Sunday Morning here, just before I went to the car boot sale. I had to leave it overnight as UA-cam was still checking for restrictions. Actually I started uploaded the 24 hours video earlier on Saturday morning, which took a couple hours, but when I went bed about midnight it was still processing so I gave up waiting. Yeah I would like to get my hands on some faulty bench PSU to repair.
These videos are gold. I have a laptop power supply that died, so opened it up and found the main fuse blown, along with the high voltage mosfet shorted and the sense resistor open. Replaced the components along with all electrolytic's but no joy, then went looking for shorts but found nothing. Its a toshiba power supply, the driver chip is unobtainable and with no simple way to test it, I put it aside until I could be motivated having another go tracking down the fault. Will definitely watch part 3 if you make it.
a good video im sure many would like to see and useful is setting up our own current limiting bulbs with dangerous mistakes ect to keep everyone safe
Thanks Richard for parts 1 and 2, looking forward for part 3. I have watched many videos on SMPS , but yours is the one that gets down to earth (no pun intended) on repairing them. Not only good explanations but also practical demonstration too. My background was linear psu's and I was shy of starting hands on repair of SMPS, but now I feel much more confident in giving them a real go. Thanks again.
“It’s AC .. it doesn’t care which way round. If you touch it (hot ground), ‘you’ will care”. Good one Richard!
Fantastic explanations! Fantastic videos!
Greetings from Brazil.
Every time I expect you to say it isn't cost effective and give up I'm thrilled to see you keep trying to fix it. Thank you for sharing your expertise and I can't wait for the next part.
Sometimes I fix stuff just for the satisfaction of it and expanding my own horizons. That's kinda how I got to here - keep on trying to fix some stuff and by doing so learn how to do it much quicker next time. 🙂 This is what I will say to anyone who wants to learn electronics repair - try to fix as much stuff as you can get your hands on, even if it costs more to fix than it is worth, and even if you can't fix it in the end, you can't put a price on the experience you gain in the attempt.
Thanks to your videos, I've managed to repair (and also understand a little better) a 230v to 12v SMPS for a Heat/Cool Box. Your explaining and commentary feels very natural and easy-going which makes it much more interesting, than watching a video where it feels like someone's just reads from a script. Keep up the good work!
That's probably because i make most of this stuff up as I go along LOL 🤣
Thank you very much Richard, a true gem for the newbies like myself!
Can't wait for part 3...cheers.
I want to thank you a lot for your videos, that i expect every day ! Thanks for your time and please continue !
your video is really helpful for beginner like me , please make a video about PWM in your all you need to know series. thank you sir
Excellent, Richard.. thanks very much for part 2. Would be interested to see those last two if you wish to do so. Also, to see when you replace those smd pwm chips.
Gracias Maestro , looking forward for part 3.
Hi Rich
following your videos and really enjoying them. I too am a fellow clayhead. from the posh end. ( sneyd green ) . i too played with electronics in the early 1970s. but lost interest but now i'm retired have started to take an interest again. learning all the things i should have learned back then. I would love to see you get those power supplies going with the new chips you ordered. and tackle the ones you ran out of time on. Loved the nostalgic bit about shorting your train transformer out with your BUGGERS . I think your explanations are very easy to understand you must have spent months in a classroom learning all this to give us a simple abridged version. My interest was rekindled by a fruit machine psu i volunteered to repair
everything works except the 44 volt output for the lamps. on power up it works then after 10 seconds or so the voltage drops away slowly down to a couple of volts having watched and understood your psu videos i reckon it's probably the feedback circuit or the chip feed capacitor gone proper leaky once warmed up. i've yet to test it. but i feel confident now i can diagnose the problem. Would love to know where in the potteries you lived. I'm watching your component explanations too. Nice and easy to understand.
Best Wishes
Paul Dickinson
Nice that the meter beeps on diode mode 😮
yep im interested for another continuation for those 2
Thanks Richard for all your hard work and sharing knowledge, I have picked up a lot of tips from watching you and another video would be appreciated...Greetings from New Zealand
Thanks once again for this👍 and yes, even though you've covered all the faults, I would like to see the last two getting analyzed.
Måns
Great job 👏
Thanks for so detailed explanation 👍👍👍
Part 3, yes please 😁👍.
keep going these videos are great. please finish the rest and let us know if replacing the chips works.
Excellent, Richard.. thanks very much for part 2. Would be interested to see those last two if you wish to do so. Also, to see when you replace those smd pwm chips.
Bravo, sir!
Learnt a bunch from this , thankyou Richard
Thanks for sharing your knowledge... Greetings from Portugal 🇵🇹 🌟
Can't wait for part 3. Thank you for the video, enjoyed every part of it.
Plenty of requests for a part 3 - I'll wait for the parts to fix the other two to arrive first - likely to take a month or more from AliExpress,
You are AWESOME Richard! Thank you, thank you, thank you! So enlightening and so passionate that I literally can’t stop watching your videos and sometimes even more than one time. Keep up the great content!
That was very good! Looking forward to to watching more.
Very interesting. The procedure for finding faults brought me a lot for these switching power supplies. A little more editing or using time lapses (for the soldering and desoldering parts) would help reduce the length of your videos. 2:24 for this one! To check if the other viewers are more or less of my opinion. Keep up this exciting work!
I guess then some others would say 'but you don't show the desoldering and soldering techniques properly, and I'm trying to learn how to do it' 😉 I'm glad you liked it though, I think we can all agree there is very little 'filler' in the videos. I think putting chapters into the long tutorials is a good compromise, but then sometimes I deliberately don't do that and sometimes even say at the start 'spend the time to watch this through and you will learn some stuff, skip parts of it and you won't' LOL
Wow the Pet Shop Boys, a real blast from the past, enjoy the concert Rich. I wonder if they will mime or actually sing. Let us know what you find out when you go see them.
Unfortunately some of the old bands don't sound anything like they did when they were in the charts. Some still sound fantastic.
Excellent video, some great techniques.
Noting that at 1:16:43 when you are measuring the from the mosfet gate to the chip, the resistor you are going across is a 000 ohm resistor/ jumper so shouldn't have been interfering with the reading on a continuity test. That would suggest perhaps that jumper has a higher resistance than it normally should?
hi Richard, enjoyed the video. I especially liked the idea of injecting 5v into the secondary side of the power supply to stabilise the feedback circuit.
What do you think to this idea? Remove the Optocoupler and replace with a diode on the primary side then measure the voltage across the capacitor near the Octocoupler and if the voltage is not stable the fault is in the primary side, if it is stable the fault is in the secondary side, any components that are shorted on the secondary side will now begin to heat up because the primary side is fully on, then use your thermal imaging camera to find the shorter component in the secondary side.
Hope you enjoy the concert with the Pet Shop Boys they make some really good songs, love them when I was a kid, but I was into the group madness and I think they're in their 70s now. time flies two fast.
I've never tried that but it may have some merit. however anything that is short on the secondary side should be easy to find anyway
@@LearnElectronicsRepair sorry Richard should have been a bit more descriptive I was thinking more in line with an ATX power supply with multiple Schottky diodes on heatsinks on the secondary side. It was not my idea, I saw it on another UA-cam video. thought I'd share it with you because I thought it was a good idea 🙂
@@davesdigitaldomain Bahhhhh, I just posted about this. You stole my thunder! Where did you see this Dave, I saw it on Haseeb's channel on UA-cam.
If you externally drive the output voltage above the normal regulation point you will drive the duty cycle of the converter to zero which means the output of the winding which powers the control circuit will produce no output. The circuit will then rely entirely on the start-up circuit. It will therefore try to start, fail, delay, try to start again and cycle forever in failure.
It isn't really common but some controller ICs, especially those with an integrated switch, will shut down if they detect excessive voltage on the switch. This can happen if the network (R, D & C) that snubs the leakage inductance spike has failed. The resistor in these snubbers often runs quite hot and may fail.
The fact that the circuit (#5 ?) worked when warmed very strongly suggests to me a flaky solder joint somewhere. There is a small chance that shift in the current transfer ratio of the optocoupler may be at play.
Thanks a lot again for your fascinating tutorials.
I hope you'd decide to fix more of them (like part 3 or something) for us. That'd be hell of a huge help:) Thanks in advance
The tube has its share of repair people who magically unsolder anything in one second top, and own 10 boutique irons that instantly melt any solder, specialized tips and all, never having any trouble thanks to the power of video editing.
It's refreshing to see somebody doing real work, struggling to cut heatshrink open or fighting with a soldering blob. Repairing stuff is a rewarding but often painful, frustrating, long and tedious task.
Your workbench somehow resembles mine. And things get disconnected, pieces wobble at just the worst moment, you never have enough fingers, the right tool is off or to the other side of the lab and you resort to undo screws with pliers and stuff :D That's my kind of workflow.
Of course, your experience and knowledge are on a different level, and I'm learning a lot. Thank you!
Interested... 👍
Does the usb-c power delivery change the basic structure of the output side? Do they require something else than an additional chip for handshake?
Thanks for the superior series! It has taught me a lot more than electrician school in 3 years.
I would change the zener and the cap. A zener in the circuit backwards provides voltage regulation.
Looking forward to part three.
When the scope showed that the transformer wasn't powering up, what would you have concluded if it had been powering up?
I have a USB charger that is pulsing 4V@1Hz on the output, so I'm wondering if the PWM is not getting its second source to VCC, and the startup circuit charges the capacitor enough to run for only a second.
If it was then about the only thing what would make sense is an open circuit secondary winding
Rich, whats your thoughts on leaky capacitors? I know you test Capacitance and ESR but how about EPR or Leakage?
Hi Richard, just noticed the link to your Patreon in the description is wrong... missing an 's'. Thought you might want to know.
Thanks Rob, I found a few more descriptions giving page not found error on the patreon link- it seems like the error crept in somehow on one of the videos in the PSU playlist a little while ago. I generally use the UA-cam option to reuse the details from a previous video (in the same playlist category) and then edit the description to suit the new video, so I must have reproduced the same error. I think I found them all now. Cheers.
If anyone would like to help support this channel you can subscribe at Patreon on this link and select your donation amount
www.patreon.com/learnelectronicsrepair
Thank you
Your videos are amazing, you explain everything simply. I really do understand transformer’s a lot more.
Richard how does a toroidal transformer differ?
Heya, 1 more good vid learned some more so that is great thanks. I'm going to make a empty bedroom into my elektronic repair hobby room to see if your explanation ( and my 30 years ago electronic school learning) are good to start repairs myself. I told a colleague of my about this and he brought me a psu like the 1 you show in 1 of your vlogs it is the 1500 W psu only this 1 is 1200W pritty simialer. I have a youtube channel is I'm gone film it and afterwards gone upload it if you like I can sent U a link wen I have uplooad it.
Thanx you for this other lovely vídeo :)
Hi Richard, very interested to see your method of testing the feedback circuit. I'm gonna try this.
I have seen another version online (from Haseeb Electronics) where he puts a diode across the primary side pins of the optocoupler, which allows him to test for issues with the feedback circuit.
An excellent into to walk warts and the fixing thereof 😁
Oh yes, do those two SMPS' too
Great Video well explained
Thank you, nice to hear you enjoyed it 😁 and good luck with your own repairs
Excellent advice as usual Dicky, thank you for sharing this information on the black art of PSU's, it really helped me to understand how they work. Please can you show the control chips repair if you can, would be nice to see the last 2 fixed 👍🏻 😁
Yes, I've ordered the parts and I will review this with a part 3 when they arrive but they will take a month or more from China, then I will look at the other two. I also have one more repair technique up my sleeve for a part three.
@@LearnElectronicsRepair that's great to hear your going to finish off the repairs, and now reading you are going to show another technique is even better, that trick you showed putting voltage on the output blowed my mind, I would never of thought of doing this but yet it made perfect sense when you explained it yeah 👍🏻 😁
@@Backcountry_Bodger ha if you liked that one you will like the other one too 😉
Fantastic videos, just great. Thank you so much for sharing that amount of well served knowledge. Very, very useful stuff. :)
Well in the first PSU you check the driver pin goes to the resistor and the other ebnd of the resistor goes to gate, but you did not notice that the resistor is zero ohm and meter didnt show that. It is possible that the first failure broke the 0 ohm resistor to the gate, the resistance drops down when parts are heated that can explain why it stabilizes () maybe even resistor on the gate drops the resistance when heated. Can you do follow up with check if chagne that 0 ohm resistor will not resolve the issue?
Of course, I will be making a part 3 anyway once the ICs arrive and yes you could be correct there about the resistor 🙂.
marsma18
I checked that gate resistor as soon as I arrived at the workshop this morning and it reads zero ohms, well spotted though.
Really good video nice test and well explained in laymens terms lol thank you keep at it 👍
Thanks sir from india
Thanks
Sending full support here
Great stuff
Thank you.
I only started working on smps after I bought a isolation transformer. But you have still be careful….
Really good. Thanks.
Richard at 1 hour why did the cap charge to 15v when the source is only 5v?
what is the main work of ceramic capacitor between hot and cold parts
Richard, can you please explain a bit more about the +vcc supply to the PWM which comes from one of the secondaries of the switching transformer? As these voltages are galvanically isolated what reference voltage is being used to provide a potential difference to feed the chip? I assume hot ground but would like a refresher on how it works, my electronics theory is very rusty (I stopped working as an electronics engineer in 1992! Love the videos BTW. Thanks, Dave
Dave Adams
Technically speaking the secondary that provides the Vcc to the PWM chip is galvanically isolated from the primary but one end of the winding is then connected to hot ground so that effectively defeats the isolation.
As the PWM chip is on the hot side of the PSU the Vcc supply does not require isolation, but it does need to be referenced to hot ground, same as the PWM chip itself is.
One may think you could use a tap on the primary winding, like an auto-transformer to supply Vcc, but this is not the case as neither end of the primary connect to hot ground. So we are not really using the secondary to take advantage of the galvanic isolation, we are doing it that way so we can efficiently create a low voltage (usually 15V) Vcc supply AND reference it to (hot) ground. Usually there is no regulation on Vcc (apart from that provided 'second hand' by the regulation of the output voltage) but sometimes there is a zener diode from Vcc to ground as I mentioned in the video.
Was there ever a part 3?
Nice teaching, the feedback circuit testing method is really amazing but i think it works only with a psu that has one output voltage, what about a psu that has two or more output voltages, i have two psu one with 5v and 12v output and the other one with different output voltages 3.3v 5v 12v 24v i've tried to inject voltage a bit higher for each output but nothing shows up on the dmm on diode mode across the optocoupler collecror to emitter pins. Thank you
nice vid
Brill very informative
Watching full pack sending support enjoy cu
Would a normal light bulb work as a cap discharger ? I have to admit im a screwdriver discharger
Go west ... with the Petshop Boys 😊
... and lets have a few more challenges !
Thank you :D
That water wheel analogy is just bizarre, especially that weird bypass circuit. It completely fails to illustrate the most fundamental operation of a flyback converter. The energy stored by the flywheel effect is, when the valve is closed, delivered to something totally lacking in the diagram - the output circuit.
When the switch turns off the vast majority of the energy stored in the inductor (so-called "transformer") is delivered to the secondary circuit. Ampere-turns are conserved. If the charge winding ('primary") has 100 turns and a peak current of 1 ampere at the instant the switch turns off and discharge winding ("secondary") has 10 turns, its current at the instant the switch turns off will be 10 amperes. That current ramps down linearly with time, all the way to zero in most flyback converter designs ("discontinuous current mode") though not in all designs. If it _does_ go to zero, the current in the charge winding and FET starts at zero and ramps up linearly with time. The diode in the output circuit prevents any current from flowing simultaneously in the charge and discharge windings.
The purpose of the snubber is to discharge "leakage inductance." Leakage inductance is modeled as a small inductance in series with the primary winding . It has no magnetic coupling to anything but itself. It is the result of imperfect magnetic coupling between the charge and discharge windings. A little bit of energy is stored in the leakage inductance when the switch is on but it can't put that energy into the discharge/secondary circuit. The leakage inductance causes a very narrow but high voltage spike as the switch (FET) turns off. The spike energy is dumped into the snubber capacitor via the diode. The resistors then discharge the cap in preparation for the next cycle. The diode is usually an ultrafast recovery type, though if the circuit is done carefully an ordinary diode can be used and the reverse recovery energy actually helps to discharge the capacitor when the switch turns on, reducing the amount of energy that has to be dissipated by the resistors across the cap. In fact with discrete FETs the avalanche energy rating of the intrinsic body diode may be adequate to handle the energy from the leakage inductance. The capacitor value is fairly critical.
Muito bom !!!!!
I have found that in some instances of an unstable output the main bulk cap would be bad. This and failed switching transistors seems to be the most common things in those cheap SMPS modules from China that you can buy off ebay as LED lighting power supplies. I can repair these things or better yet out of the box "upgrade" them with better transistors and caps, though I do have a youtube channel I am not good at presentation and explanation of what I am doing and why. I have a few videos on communications related electronics and some video gam related stuff but they are nothing to write home about.
My thinking is maybe a video covering those SMPU modules that are rated over 10 amps and of 5 and 12 volts types since there are plenty of videos on 24 volt 10 amp versions out there. Reason I mention over 10 amps is because the actual design of the SMPU changes physically.
Cool...
Where are the little tiny ones that weigh 30 grams ?
I from Congos
You are going to change that 20 Amp (ho, ho) piece of tinned copper wire for a 0 Ohm resistor aren't you?
Nahh it will just stop the resistor from blowing again LOL. It's not like it is supposed to be a fuse and a lot of current can't really flow that way due to the 3x 180K resistors in parallel. Actually I'm a bit surprised the 0R went open at all - or the blown up track. Looks like some sort of liquid got into the PSU if you ask me, but there is nothing around there for liquid to short to
@@LearnElectronicsRepair Liquid is to be expected in power supplies fitted with pumps and waterwheels. Ho, ho.
@@ralphj4012 Ain't that the truth 😅😅😅
Stop with commertials please
Fascinating to see how these devices work, but why bother repairing them? However little you pay yourself per hour, it makes no economic sense.
Interesting UA-cam videos like this one are a form of software since you make it once and every view counts as revenue. That is the economic explanation and that is why you will find lots of videos in UA-cam that don’t make sense but they do through the UA-cam lens.
Good work.
Love the take a picture with a phone, " modern technology of this day " for me this look to be a hold technology 🤣🤣
I like the ol' e SWASTICKA looking resistor at the beggining AUSSIE AUSSIE AUSSIE!!!!@!........ OE,OE ,OE.....😅😅😅😮😢😂😀🫠😃😄😁😅😅🤣😂😂😂😂😅😆😁😉😉😉😉😉😉😉😉😉😉😉😉,
JUST KIDDING MAN.....😢😢??