Okay, maybe it's not economical to fix as a repairman. But that's a far cry from not being worth repairing. There's so much more to it than just economy. Experience, morals, ethics, the concept of not creating more ewaste, ... I'm for one proud I can repair things rather than tossing it!
Repairing junk is so much fun and rewarding, sometimes exciting or even frustrating. I'd even say it's one of the more emotional hobbies. Too bad that nobody around me shares my interests. It's sad that I have to watch vids of ppl repairing stuff on the other side of the world.
The real value for me repairing the stuff that is uneconomical to repair, is the educational value. You learn so much trying to repair those things, both in reverse engineering stuff that doesn’t have a circuit diagram available and learning some tricks that they use in equipment unfamiliar to you, as well as to how that type of equipment works, even though it might take a long time to repair.
Exactly. In this case I also might end up getting more of those PSUs so investing some time understanding how they work at the beginning will allow you to pinpoint new issues in the future in less time.
Hi Tony, and nice job, as usual! Thank you so much for mentioning me! I know i have to switch to English soon, it's just that i fear my English accent is horrible and will turn people off, but i will try it none the less. About the video. The main advantage of switching power supplies is their size, they are usually much smaller than their linear counterparts. The reason is that the higher you go in frequency, the smaller the magnetics and filter caps can be. There are allot to say about the magnetics size related to frequency, but most of it can be summed by the fact that the higher the frequency, the smaller the number of turns ( of the coils/windings ) needed for a given core size, one simple way to view and understand it is that with higher frequency, each cycle the winding "sees" its voltage less time, thus less magnetic force ( less B ) on the core. Also, the switching action means they can regulate any voltage with much, much higher efficiency ( the power devices are always either fully on, or fully off, thus losses on them are small, direct conduction and switching ), so heatsinks are way smaller. PWM indeed always deals with a fixed frequency, and regulation is obtained by modulating the duty cycle, with the help of the LC tanks on the outputs. There are another class of switching supplies that modulate the frequency in order to regulate the output, they are called resonant switching supplies ( LLC for example ), they use a resonant LC tank on the primary side of the supply with which the output is regulated by modulating the frequency. Ah, and just one more thing ( you know me and my "one more things" ), all switching supplies that rectify the direct voltage on the secondary ( forward with one or two transistors, half bridges, full bridges, push pull ) have a TRANSFORMER ( all PWM ones anyway, let us not enter the resonant discussion still ), that basically works the same way as the 50/60Hz transformer ( the basics ), just at a much higher frequency. Flyback supplies on the other hand, although most of the paperwork on then relate to them as also having a transformer, still it is best to view it a a coupled inductor with two or more coils. That is because just like in the basic boost regulator, the diode on the output rectifies the "flyback" voltage, so does the rectification on the outputs of any flyback supply, their output diodes are "ON" when the primary mosfet is "Off", when the coil generates its "flyback" voltage ( with reverse polarity ).
Thanks for the extra info, always welcome a very easy to understand! You don't have to do anything of course. And there are many succesfull youtubers with thick accents (and I am sure I have my own as well of course) but people don't care if the content is good. That said, as I keep saying, take your time! But please don't feel that you have to do anything! :) Thanks again for all your help :)
Nice job. We all learned something. I don't think I'll ever get bored by good SMPS repairs. But now we'll never know if that broken cap was the reason Vref wasn't smoothed out properly before, preventing the whole thing from switching. That poor chip might be totally innocent. You know it ;-)
Yes good point. Those ICs are not expensive so I didn't think of soldering the old back in - you know, every time you solder and de-solder those traces weakens. I could have left the broken capacitor in place and test though.
I had a similar case where the power supply started during measurements, but the culprit was a small electrolytic decoupling capacitor for controler IC. The golden rule with capacitors is that the smaller the size, the sooner it needs to be replaced. In application notes, such capacitors have the shortest lifespan.
oh cool! That's why I see capacitors of the same series with different ratings, I never considered that. I've just checked the FR series datasheet and indeed it's as you said. Thank you! I did replace the startup capacitor just for precaution.
It's almost always the caps on any piece of equipment. Flat panel displays, power supplies, motherboards, and start/run caps on a variety of motor driven equipment. First thing I do is look for the bulge.
Let me chime in with another vote for "the Vcc cap for the chip might be the real culprit as well". Everything you saw on your scope with the supply not operating is consistent with the chip failing to start up and ending up in hiccup mode: @13:19 - we are seeing the Vcc cap being charged through the startup resistor (rising part of the "sawtooth"), but then being discharged quite quickly when the chip reaches the startup threshold, until Vcc drops to the under-voltage lockout (UVLO) threshold. The Vcc cap needs to power the chip until switching starts to produce energy on the auxilliary winding, which does not start till UVLO kicks in. @14:55 - While the chip is not running (because the startup voltage has not yet been reached or UVLO kicked in), the VREF regulator is turned off. So you would expect to see 7.5V while the chip is running and ~0V when the chip is suspended. The width of the pulses here is approximately consistent with the width of the falling slop at the Vcc pin (the time the chip is running). @16:30 - This might be the death knell to the theory the Vcc capacitor is to blame. For the Vcc to be powered from the Aux winding instead of the startup resistor, there need to be switching pulses. On the other hand, you are looking at just one of the two switch outputs, possibly the first pulse happens on the other one, and UVLO already kicks in before the pulse on this output is generated. The startup resistor that charges the Vcc cap *does not supply enough current to power the chip while it is operating*. So there is a "take-over" period in which the chip draws its higher operating current instead of the really low standby current, but does not yet get powered from the aux winding. During that period, the Vcc cap is the only source of power for the chip. If the capacity is too low or the ESR is too high, the time period that the Vcc cap is able to power the chip is not sufficient for the supply to start up and generate its own supply voltage from the aux winding. I see three possible explanations why swapping the controller chip and the broken 100nF cap fixed the supply: - The controller chip was acutally broken. - The replacement chip you installed uses less power during startup than the old one, so a marginal Vcc cap is sufficient for the replacement chip but unsufficient for the old chip. - The Vref cap was already broken (i.e. the leg disconnected) before you desoldered the old chip, and the missing capacitance on Vref caused the actual issue. Your work on the PCB just caused the broken capacitor to be more visible. Whenever you decide to recap a SMPS, in my oppinion you should always recap the Vcc capacitor for the controller chip as well as the output capacitors. I've seen so much SMPSs failing due to the startup cap getting bad that I would never skip that one on preventive maintainance.
Thank you for taking the time to share this very useful insight. I can confirm I have also swapped the startup capacitor, as you say, it makes sense to do that as preventive maintenance. I might want to go back and check whether the VCC is now more stable than before. I agree with everything you say, maybe the IC was good. Though my hot air was running VERY slowly, I doubt I warmed up that electrolytic. If anything, it might have been that VREF capacitor which is very close to the IC. Thanks again!
In SMPS the poor power factor is caused by the input rectifier with smoothing capacitor. The problem here isn't the phase shift between voltage and current, the problem is the non-sinusoidal shape of the drawn current, which has a lot of harmonics, especially the cosinusoidal harmonics are the problem, since they are 90 degrees out of phase from the sinusoidal harmonics. The APFC makes sure, that the current drawn from mains is always a sinewave. Since the APFC is a boost converter, it also provides a stable enough voltage for the more powerful power converter topologies, like half-bridge or forward. It also means, that it doesn't matter, if you plug it in EU, where we have 240V or US where they use 110V. PFC explained. :)
Finally someone who speaks in a way I understand. I have been looking for someone doing a video on the controller chip with a scope. I’m testing an RCA surround sound receiver and I’m trying to test the controller IC. This video is really helpful for me so a BIG thanks.
@10.00 that behaviour is probably the small capacitor near the chip, heat can bring back a capacitor a little when it is marginal. Could also be something as simple as a bad solder joint in that area.
It could be it course. Though the hot air was running really slow and at not too high temp . The PSU is still working BTW so I am confident it was the IC.
Great job. Very thorough job of extracting fault. The only issue I have is that when I'm watching this, it's really easy, but gets infinitely more difficult when I'm trying it.
This is the best PSU video I've watched and I should know I've watched a few. Seriously though my understanding of switch modes just got a whole lot better.
Great video! You should replace small caps near the IC that you swapped too though. One of them is a bootstrap capacitor working as a power source during startup and this is most common problem in most of the power supplies.
Mitico Tony! un altro bellissimo video, spiegazioni chiare e lineari, ottima composizione grafica e... quel pizzico di autoironia che strappa il sorriso 😄🥰 Not to mention the perfect English proficiency and accent that makes impossible to have clues about your country of origin 😉
the short basic theory behind why the SMPS is much more compact is that transformers change the electrical energy into magnetic energy then back to electrical -- but for the magnetic energy the transformer's core should have enough capacity to "take it up" (not get saturated) which is depending on the power and the length of the electromagnetic cycle -- so for big power you need a big core if the cycle is slow or for the same power use faster cycle that requires smaller core thus smaller transformer And to do that it first makes DC, then a switching transistor chops it up and feeds the transformer with high frequency electricity. Then the secondary side just rectifies and smooths it (then there are feedback and protection and filtering and yada-yada....)
Nice diagnostics and fix. Must say thats a very neatly designed power supply. Regarding the differently labeling on the IC's they could have be pulled from E-waste and indeed different years/batches. Considering you mention its around 20 years old replacing the capacitors is certainly a good idea as its around the capacitor plague era.
Thanks! The ICs were definitely brand new - or they ironed them back to perfection :) ah good point about the capacitor plague era. I believe those were just after that, I've never seen those PSUs with bad caps. Yet, I think it makes sense, particularly because they installed a power resistor between them running at 100C :D
@@tony359 back to perfection costs to much money so they might indeed be new (old stock) in that case. we had a Packard Bell around 2005 that had all the capacitors on the MSI main board and the PSU bulged and leaking. It was built after the official capacitor plague manufacturing dates probably used up the stock they had. They were high temperature Panasonic branded caps making it extra wierd. So not trusting any capacitors around the 20 year mark anymore😉
Why does it matter about the plague era? Nichicon of course had some suspicious capacitors over the years very few, because that's just the way things go, but they weren't part of the "plague" per se were they.
Differential probes are not too expensive. Alternatively these days you can get a battery powered scope - it should work in a similar fashion. But you need to make sure your probe can withstand the voltage and you must not ground anything at any time.
Blessings, Tony !!! Wonderfull job showing some others perspectives of this activity. I´m learning so much from your videos. I wish I had your knoledge, skills and experience !!! Blessings again !!!
Thanks for clarifying the operation of the power supply. It was always a mystery to me how the regulation worked because schematics for these items is non existent .
The controller datasheet has a "standard" schematic on it which you can use to understand how an SMPS works. Failing that, check this out: danyk.cz/s_atx_en.html There are MANY schematics with different topologies.
Thank you, Tony, for this great repair! I always learn something new watching your videos. Greetings from Italy💪 Keep up with this kind of video, great job!
G'day Tony. These power supplies are great to have on hand, or at the workbench. Very easy to modify into Variable Outputs, AC and DC, current limiting, and Isolated Outputs. (Good replacement for Commodore and Amstrad computers) Unfortunately, Some do suffer from cheap components, usually the controller chip. The older versions (late 80's to late 90's) are very robust. That 👉single👈Hi Voltage Capacitor is a failure point. I would normally add a second with similar, but not the same, spec's. Cheers.😉
Interesting, you mean the main 450V capacitor? I usually don't replace them as they are expensive and at that point you start questioning whether to invest in a repair or get a new one. Also space on that side of the board is limited. But I'll keep that in mind thanks!
Yes, very good point - I might keep it for a future repair. Though the spares were cheap and wondering if I wanted to solder and de-solder it twice risking to damage the traces... uhm... Thank you!
I didn’t install the socket on purpose on this occasion. There are 340V nearby, I don’t want that IC to come off for whatever reason. Anywhere else, 100% 🙂
I think you're probably safe with parts that have silkscreened part numbers. The dodgy parts all seem to have their part numbers laser etched, probably because it's easier.
Probably yes. I'm also wondering whether it would make any sense to "fake" an SMPS controller IC? A power transistor sure, you can sell cheaper stuff for more money. But an SMPS controller? Either it doesn't work or it's genuine and works :)
@@tony359 if there was a particular SMPS controller that was widely used and popular they probably would! I guess there's a smaller selection of high power MOSFETs that are commonly used so they tend to get faked. Good to see it worked though, another success!
@@tony359 Whether it makes sense or doesn't, someone out there does it ROUTINELY to all the salvaged circuits, taking off the top surface and repainting the manufacturing date. Perhaps they have found that when one seller sells "new" ICs and another seller sells "used" ICs, the one with the "new" ones is less likely to get stuck with inventory hogging their shelves, and they have the technology so they're going to use it. And i disagree about lasered. My Yamaha YM3438 soundchips are definitely ones that have been remarked and they're silkscreen marked, not lasered. Yes they actually are YM3438s but they are definitely salvaged and definitely not from batch and year claimed.
The reason is the inductive reactance of the coils of the transformer. For higher frequency you need less turns of each winding. That is why you can make it smaller.
Nice fix, but I think you should have also replaced the small electrolytic that does the startup supply for the IC, small caps usually die first, I’ve fixed several power supplies just by replacing the start up capacitor.
Symmetrical powersupplies are not only for balanced outputs. Nearly every opampcircuit needs it to function properly. You could use voltage dividers and have a so called "virtual earth", but this isn't exactly how good audio circuits should be built.
Hi Tony! - I follow your advice and dont mess with power supplies Not because of the explanation you and other people give about the basics of its operation That I understand... the big components I understand, the bridge rectifier, the switching transistors etc But it is all that ARMY of small components there, resistors, ICs, capacitors that really scares me... it seems there is so so so much more going on there Dont tell me all those dozens of tiny componentes are all just for the voltage sensing and feedback circuit....
oh well, I don't know that myself! :) Sometimes I feel those PCBs are designed with random "seeds" added to the PCB just to scare normal people like us :) Thanks for watching!
Excellent vid. Just wonder if the Cap was half broken and the heat was making it good and the controller might be ok? Only thing i might have done is put in a socket for a few cents and makes switching and testing out parts to narrow down a little easier and if it comes back again?
Yes that is a possibility. I intentionally soldered the IC on the PCB because it's the primary of a power supply. Call me over-cautious but there are 340V nearby :) Those ICs are cheap, not a big deal. Thanks for watching!
@@tony359 Yes, you are right. Normally, theres a metal barrier with the mosfets of pri and sec making it pretty safe, and i suppose a little hot glue on both sides of the chip will stop it coming out and easy to replace again if its "chinese" and not going to last long time. I had a bad controller on a tek Oscilloscope but the board was all one piece and insanely hard to get to the power section so i put in a socket there just so i could pop it out easily next time and main power was actually 42V coming from a power brick with fusing but i put my own just for added protection as a hot wire can come loose any time too flail around and short on any PS. Just found your channel and will go back and watch you old vids as very instructive. I fix (try) a lot of laptop M/B's these days but always learning so if you can do some of those, that be great too.
The truth is that if that PSU fails again, it'll likely end up in a bin I'm afraid. Shipping also can do wonders. I shipped one PSU like that years ago and it arrived at destination with the PFC transformer (I know it's not a transformer, you get what I mean) RIPPED from the board. But the metal cage was undamaged. HOW! :)
Very informative video, Tony; I’ve just subscribed to your channel. Keep up the good work, mate, and pay zero attention to the haters; it’s a bloody strange world online these days.
Just one tiny nitpick... Although I agree I don't expect the IC to be changed on a regular basis, I would have socketed it. Then again, that does introduce another layer that *may* cause issues... So, now I'm not so sure about my own nitpick... :P
Hi - thanks for your comment! It was intentional to be honest. On anything else, by all means. On the primary of a power supply with 340V running around, I prefer to have everything soldered on the PCB :) Thanks for watching!
If you already replacing caps - at least check the high voltage one. People often do not even check them as they're mostly good but that's more "good enough" than good after 20 years. Even with low frequency of main network transformer still stress them with high frequency depletion and sitting there in the middle of heatsinks doesn't help. They're working closer to rated voltage (sometimes just 10-30V under it) also putting additional stress on them. Also small cap (usually 10-22uf/50V) next to control IC is common point of failure, replacing it with new quality cap is more important then replacing good measuring output capacitors.
The only pin you did not measure after you got it working was the vcc, I suspect this will show you the cap is duff on VCC and you saw the ripple on VCC when it was not starting I am upto 20mins so far. I stick by my diag, just the new IC is more tolerant. I repair quite a lot of PSU's and the cap is the most common replacement, in fact I repaired a medical grade PSU tonight and it was a 100uf 35V on pin 7 of a 3842 IC. I rarely replace PSU IC's unless it has blown the output FET then it usually kills the ic. On the other hand if a TOPxxx ic is not working that is much more common.
I can measure again but the PSU is still working after many hot-cold cycles. I believe (not sure) that that amount of ripple is normal when the PSU has not started yet.
@@tony359 I assume the new ic is more tolerant of the dropping DC on VCC. I would replace it anyway and measure the ripple on the replacement. Curiosity getting the better of me.
To be honest the capacitors I would change automatically are the tantalum beads. They are notorious for going short circuit and, after 20 years I wouldn't trust them.
Likely it was broke but you did not see it, and when you heated, it heated the pad enough to move just a bit to have a gap. So the IC could possibly be fine ... who knows.
nice repair, Tony, but since this is about a PSU, one question: you take 240V from the outlet and then the PSU increases it to 340V, in this case. why? why does it have to do that so the end result is just 5V, or 15V. wouldn't it be easier from 240 to 5 rather than 240 - 340 - 5?
Because you don't really have a choice - it happens automatically when you rectify mains voltage. The mains voltage swings up and down between positive, going through zero, to negative, back to zero and then positive again in a continuous sinewave. The rectifier allows energy to flow into the smoothing capacitor as long as the mains voltage is higher than the voltage the capacitor is at. Once the sinewave goes back towards zero again at the end of the swing, the rectifier acts like a check valve and the capacitor remains charged at the highest voltage the mains hit. This repeats over and over again and keeps the capacitor charged at near the peak mains voltage which, in Europe and the UK, is around 340V(*) *) We say the mains is 240V because that's the effective voltage, basically the "average" (not exactly - it's complicated) between all the intermediate voltage levels the sinewave goes through as it swings up and down. The peak voltage that the sinewave hits is actually 1.41 (square root of 2) times higher than that, which is where the figure of approximately 340V comes from.
Thanks - Sorry I didn't explain that. It's just what you get when you rectify 240V AC to DC via bridge rectifier and smoothing capacitor. It's inevitable unfortunately :) Mains is using high voltage to minimise loss due to higher currents: Voltage and Currents are linked when it comes to power. So to transfer a certain amount of power from A to B you can either use high voltage and low currents (small wires) or low voltage but high current (big wires and big losses). Here in the UK, we use 110V in building sites where accidents are more likely. We have 110V tools for that purpose only. It won't be safe but it's... safer - actually it's "less dangerous" :)
240V is RMS voltage. After you rectify the voltage and charge a capacitor you have peak voltage. Which is going to be RMS times 1.414 or 339.36 VDC. Minus the voltage drop of 2 diodes in the bridge. But let's not get too technical. A sine wave is up and down and RMS is 0.707 of the peak reading. So when the cap bulks the wave up you get close to peak voltage. Or you can just chalk it up to magic and call it a day too.
Me: "I'm bored, I don't know what to watch..." Tony: "How about me fixing a power supply?" Me: "Son of a gun, I'm in!" >> clicks like, proceeds to watch
Good morning…, great video, and well explained. My recommendation is to slow down slightly in your explanation. It’ll help those in learning the hobby. Kindest regards!
I noticed you keep saying 'cage'. Out of curiosity: is that a common thing? I'm not an native english speaker but isn't "housing" a better word for it? Enjoyed the video nonetheless Tony! Always do! Keep up the good work!
Housing sounds good - cage might be less accurate indeed. I have said much worse things on this channel when it comes to English :) Thanks for watching!
@@tony359 considering that Romanian is a distant relative of Italian... if they don't speak it too fast I'll understand the meaning, but not the whole text.😅
The actual fault could have been a bad solder joint or the cap that broke during de-soldering. From a 35 min video I expected some more in depth analysis, instead of just replacing a part and be done with it.
You are right - it's hard to say. I'm curious: I've scoped the IC before and after, explained how an SMPS works, what kind of "in depth analysis" were you expecting? I'm just asking, not challenging.
@@tony359 I would have proceeded in the following order: 1) re-flow all solder joints 2) replace the broken cap 3) replace the IC, and checked functionality between those steps That is from simple to complex, and that would have identified the actual problem. By replacing the IC and the cap without checking functionality in between you never know unless you do some further analysis, for example put the old IC back in.
Yes, I could have replaced that cap and check - but does that qualify as "lack of in depth analysis"? I noticed the cap was broken AFTER I de-soldered the IC. Re-solder the IC and - potentially - having to de-solder it again will have probably caused some damage on those small traces - sockets are not an option on an SMPS in my opinion. The only thing I couldn't pinpoint 100% is whether the issue was the cap or the IC.
@@mojoblues66 sure but as I said, soldering-desoldering an IC on that PCB will eventually cause some damage. Particularly if I had soldered it back and ascertained it was indeed faulty, so more soldering would be required.
Size of components has nothing to do with signal frequency in this context. Switching power supply works on a principle of controlled collapsing of magnetic field in transformer which causes a flow of vast amounts of energy through output circuit. Timing of this magnetic field fluctuations is controlled by an optically isolated feedback loop in order to minimize risk of high voltage appearing on the secondary side. That's like 80% of theory of switching supply operation. Trying to fix such a PSU with so little knowledge of schema and functions performed by its components ends just like here - a lot of missed conjectures and surprises. Not a good material to educate people, to be honest.
Thank for your comment - though I'm not sure the frequency has nothing to do with size. Would you be so kind to tell me where I said that I am trying to educate people here?
Nobody cares, this is crap
Good morning to you too!
You can call me "Nobody", I do care... 😘
@bussi7859
Careful, your ignorance is showing..
@@tony359 Tony pins it and says: "Good morning to you too!" PERFECT... Made my day!
@bussi7859 I think you should get help from a good therapist because you need it !!!
Okay, maybe it's not economical to fix as a repairman.
But that's a far cry from not being worth repairing. There's so much more to it than just economy.
Experience, morals, ethics, the concept of not creating more ewaste, ...
I'm for one proud I can repair things rather than tossing it!
Of course and that’s what I normally do 🙂
Repairing junk is so much fun and rewarding, sometimes exciting or even frustrating. I'd even say it's one of the more emotional hobbies. Too bad that nobody around me shares my interests. It's sad that I have to watch vids of ppl repairing stuff on the other side of the world.
I don't get queues of people eager to watch my repairs either, don't worry :)
The real value for me repairing the stuff that is uneconomical to repair, is the educational value. You learn so much trying to repair those things, both in reverse engineering stuff that doesn’t have a circuit diagram available and learning some tricks that they use in equipment unfamiliar to you, as well as to how that type of equipment works, even though it might take a long time to repair.
Exactly. In this case I also might end up getting more of those PSUs so investing some time understanding how they work at the beginning will allow you to pinpoint new issues in the future in less time.
Hi Tony, and nice job, as usual!
Thank you so much for mentioning me!
I know i have to switch to English soon, it's just that i fear my English accent is horrible and will turn people off, but i will try it none the less.
About the video.
The main advantage of switching power supplies is their size, they are usually much smaller than their linear counterparts.
The reason is that the higher you go in frequency, the smaller the magnetics and filter caps can be.
There are allot to say about the magnetics size related to frequency, but most of it can be summed by the fact that the higher the frequency, the smaller the number of turns ( of the coils/windings ) needed for a given core size, one simple way to view and understand it is that with higher frequency, each cycle the winding "sees" its voltage less time, thus less magnetic force ( less B ) on the core.
Also, the switching action means they can regulate any voltage with much, much higher efficiency ( the power devices are always either fully on, or fully off, thus losses on them are small, direct conduction and switching ), so heatsinks are way smaller.
PWM indeed always deals with a fixed frequency, and regulation is obtained by modulating the duty cycle, with the help of the LC tanks on the outputs.
There are another class of switching supplies that modulate the frequency in order to regulate the output, they are called resonant switching supplies ( LLC for example ), they use a resonant LC tank on the primary side of the supply with which the output is regulated by modulating the frequency.
Ah, and just one more thing ( you know me and my "one more things" ), all switching supplies that rectify the direct voltage on the secondary ( forward with one or two transistors, half bridges, full bridges, push pull ) have a TRANSFORMER ( all PWM ones anyway, let us not enter the resonant discussion still ), that basically works the same way as the 50/60Hz transformer ( the basics ), just at a much higher frequency.
Flyback supplies on the other hand, although most of the paperwork on then relate to them as also having a transformer, still it is best to view it a a coupled inductor with two or more coils. That is because just like in the basic boost regulator, the diode on the output rectifies the "flyback" voltage, so does the rectification on the outputs of any flyback supply, their output diodes are "ON" when the primary mosfet is "Off", when the coil generates its "flyback" voltage ( with reverse polarity ).
Thanks for the extra info, always welcome a very easy to understand! You don't have to do anything of course. And there are many succesfull youtubers with thick accents (and I am sure I have my own as well of course) but people don't care if the content is good. That said, as I keep saying, take your time! But please don't feel that you have to do anything! :)
Thanks again for all your help :)
You don't have to switch to English for me... vorbesc romaneste. :)
(edit) subscribed.
All you'd do with an accent, is reveal you're an international person. That's not the end of the world, luckily
Nice job. We all learned something. I don't think I'll ever get bored by good SMPS repairs. But now we'll never know if that broken cap was the reason Vref wasn't smoothed out properly before, preventing the whole thing from switching. That poor chip might be totally innocent. You know it ;-)
Yes good point. Those ICs are not expensive so I didn't think of soldering the old back in - you know, every time you solder and de-solder those traces weakens. I could have left the broken capacitor in place and test though.
@@tony359 I know. But now your viewers will toss and turn in bed the whole night brooding over the unanswered question: Cap or chip?
Oh No! :D
I had a similar case where the power supply started during measurements, but the culprit was a small electrolytic decoupling capacitor for controler IC. The golden rule with capacitors is that the smaller the size, the sooner it needs to be replaced. In application notes, such capacitors have the shortest lifespan.
oh cool! That's why I see capacitors of the same series with different ratings, I never considered that. I've just checked the FR series datasheet and indeed it's as you said. Thank you! I did replace the startup capacitor just for precaution.
I've never stumbled across that correlation; gonna keep a closer eye out when looking over data sheets. Thanks for sharing.
It's almost always the caps on any piece of equipment. Flat panel displays, power supplies, motherboards, and start/run caps on a variety of motor driven equipment. First thing I do is look for the bulge.
Let me chime in with another vote for "the Vcc cap for the chip might be the real culprit as well". Everything you saw on your scope with the supply not operating is consistent with the chip failing to start up and ending up in hiccup mode:
@13:19 - we are seeing the Vcc cap being charged through the startup resistor (rising part of the "sawtooth"), but then being discharged quite quickly when the chip reaches the startup threshold, until Vcc drops to the under-voltage lockout (UVLO) threshold. The Vcc cap needs to power the chip until switching starts to produce energy on the auxilliary winding, which does not start till UVLO kicks in.
@14:55 - While the chip is not running (because the startup voltage has not yet been reached or UVLO kicked in), the VREF regulator is turned off. So you would expect to see 7.5V while the chip is running and ~0V when the chip is suspended. The width of the pulses here is approximately consistent with the width of the falling slop at the Vcc pin (the time the chip is running).
@16:30 - This might be the death knell to the theory the Vcc capacitor is to blame. For the Vcc to be powered from the Aux winding instead of the startup resistor, there need to be switching pulses. On the other hand, you are looking at just one of the two switch outputs, possibly the first pulse happens on the other one, and UVLO already kicks in before the pulse on this output is generated.
The startup resistor that charges the Vcc cap *does not supply enough current to power the chip while it is operating*. So there is a "take-over" period in which the chip draws its higher operating current instead of the really low standby current, but does not yet get powered from the aux winding. During that period, the Vcc cap is the only source of power for the chip. If the capacity is too low or the ESR is too high, the time period that the Vcc cap is able to power the chip is not sufficient for the supply to start up and generate its own supply voltage from the aux winding.
I see three possible explanations why swapping the controller chip and the broken 100nF cap fixed the supply:
- The controller chip was acutally broken.
- The replacement chip you installed uses less power during startup than the old one, so a marginal Vcc cap is sufficient for the replacement chip but unsufficient for the old chip.
- The Vref cap was already broken (i.e. the leg disconnected) before you desoldered the old chip, and the missing capacitance on Vref caused the actual issue. Your work on the PCB just caused the broken capacitor to be more visible.
Whenever you decide to recap a SMPS, in my oppinion you should always recap the Vcc capacitor for the controller chip as well as the output capacitors. I've seen so much SMPSs failing due to the startup cap getting bad that I would never skip that one on preventive maintainance.
Thank you for taking the time to share this very useful insight. I can confirm I have also swapped the startup capacitor, as you say, it makes sense to do that as preventive maintenance. I might want to go back and check whether the VCC is now more stable than before.
I agree with everything you say, maybe the IC was good. Though my hot air was running VERY slowly, I doubt I warmed up that electrolytic. If anything, it might have been that VREF capacitor which is very close to the IC.
Thanks again!
In SMPS the poor power factor is caused by the input rectifier with smoothing capacitor. The problem here isn't the phase shift between voltage and current, the problem is the non-sinusoidal shape of the drawn current, which has a lot of harmonics, especially the cosinusoidal harmonics are the problem, since they are 90 degrees out of phase from the sinusoidal harmonics. The APFC makes sure, that the current drawn from mains is always a sinewave. Since the APFC is a boost converter, it also provides a stable enough voltage for the more powerful power converter topologies, like half-bridge or forward. It also means, that it doesn't matter, if you plug it in EU, where we have 240V or US where they use 110V.
PFC explained. :)
I was able to follow about 95% of this video - and then you just blow my mind.
There's more to learn...
Well done! 👍
As exciting as a motherboard? :)
@@tony359 meh. No. :-)
@@Bergi2000 nah it is if it boom booms it is exciting
@@tony359 Only if you touch the spicy Cap. 337V is very exciting.
ahah - I'm happy to leave all that fun to others! ;)
Finally someone who speaks in a way I understand. I have been looking for someone doing a video on the controller chip with a scope. I’m testing an RCA surround sound receiver and I’m trying to test the controller IC. This video is really helpful for me so a BIG thanks.
You are very welcome, I hope you can succeed in your repair! :)
Not many channels delve this deep into electronics. Always fun to watch! :)
Thank you for your kind words, they're much appreciated! :)
This is among the best, well explained SMPS repair videos I've seen yet. Great stuff Tony.
Your kind words are very welcome! Thank you!
I so enjoyed your troubleshooting methodology and thoroughness, including explanations. Thank you!
Super happy you enjoyed it thanks!
@10.00 that behaviour is probably the small capacitor near the chip, heat can bring back a capacitor a little when it is marginal.
Could also be something as simple as a bad solder joint in that area.
It could be it course. Though the hot air was running really slow and at not too high temp . The PSU is still working BTW so I am confident it was the IC.
Learned a few things, thank you, sir!
Very, very entertaining.
thanks for your kind words!
Great job. Very thorough job of extracting fault. The only issue I have is that when I'm watching this, it's really easy, but gets infinitely more difficult when I'm trying it.
eheh, don't worry, it's not so easy for myself either :) Thanks for watching!
This is the best PSU video I've watched and I should know I've watched a few. Seriously though my understanding of switch modes just got a whole lot better.
Thank you! it's really kind of you to say!
Great video!
You should replace small caps near the IC that you swapped too though. One of them is a bootstrap capacitor working as a power source during startup and this is most common problem in most of the power supplies.
I have already off camera, but thanks for mentioning!
This is the most I ever learned in 35 minutes. Bravo
Thanks for your kind words! :)
Learnt a lot about how an SMPS works. Thanks Tony.
you're very welcome, thank you for watching!
Mitico Tony! un altro bellissimo video, spiegazioni chiare e lineari, ottima composizione grafica e... quel pizzico di autoironia che strappa il sorriso 😄🥰 Not to mention the perfect English proficiency and accent that makes impossible to have clues about your country of origin 😉
ahah grazie! Ogni tanto mi domandano se sono Francese, lo prendo come un complimento! :)
Very good explanation of the chip operation would never have known otherwise, very professional presentation. Thanks for sharing.
Thank you for your kind words!
No argue on swapping out electrolytic capacitors since they already wear out during use.
the short basic theory behind why the SMPS is much more compact is that transformers change the electrical energy into magnetic energy then back to electrical -- but for the magnetic energy the transformer's core should have enough capacity to "take it up" (not get saturated) which is depending on the power and the length of the electromagnetic cycle -- so for big power you need a big core if the cycle is slow or for the same power use faster cycle that requires smaller core thus smaller transformer
And to do that it first makes DC, then a switching transistor chops it up and feeds the transformer with high frequency electricity. Then the secondary side just rectifies and smooths it (then there are feedback and protection and filtering and yada-yada....)
makes sense, thanks!
Thanks for the explanation.
Nice diagnostics and fix.
Must say thats a very neatly designed power supply.
Regarding the differently labeling on the IC's they could have be pulled from E-waste and indeed different years/batches.
Considering you mention its around 20 years old replacing the capacitors is certainly a good idea as its around the capacitor plague era.
Thanks! The ICs were definitely brand new - or they ironed them back to perfection :)
ah good point about the capacitor plague era. I believe those were just after that, I've never seen those PSUs with bad caps. Yet, I think it makes sense, particularly because they installed a power resistor between them running at 100C :D
@@tony359 back to perfection costs to much money so they might indeed be new (old stock) in that case.
we had a Packard Bell around 2005 that had all the capacitors on the MSI main board and the PSU bulged and leaking.
It was built after the official capacitor plague manufacturing dates probably used up the stock they had.
They were high temperature Panasonic branded caps making it extra wierd.
So not trusting any capacitors around the 20 year mark anymore😉
Why does it matter about the plague era? Nichicon of course had some suspicious capacitors over the years very few, because that's just the way things go, but they weren't part of the "plague" per se were they.
I think everybody was?
I really must get a differential probe its a lot saver than just an isolation transformer. Excellent video thank you
Differential probes are not too expensive. Alternatively these days you can get a battery powered scope - it should work in a similar fashion. But you need to make sure your probe can withstand the voltage and you must not ground anything at any time.
Very nice and Im impressed a romanian helped you, that DjMarik78 dude. Very cool.
Blessings, Tony !!!
Wonderfull job showing some others perspectives of this activity.
I´m learning so much from your videos.
I wish I had your knoledge, skills and experience !!!
Blessings again !!!
Thank you for your kind words!
Thanks for clarifying the operation of the power supply. It was always a mystery to me how the regulation worked because schematics for these items is non existent .
The controller datasheet has a "standard" schematic on it which you can use to understand how an SMPS works. Failing that, check this out: danyk.cz/s_atx_en.html There are MANY schematics with different topologies.
@@tony359😊
Great work. Thank you for this content! Greets from germany.
Thank you for your kind words!
Thank you, Tony, for this great repair! I always learn something new watching your videos. Greetings from Italy💪 Keep up with this kind of video, great job!
Saluti dalla piovosa Gran Bretagna!
Da che parte dell'Italia scrivi?
Da Verona e anche qui piove😁☔️ complimenti ancora per la riparazione💪
Eh dai, prima o poi il sole li' arriva. Qui chissa' :D Grazie!
GREAT VIDEO , and as a experienced electronic constructor - i've learned something new. Thank you ! 👌
Thanks for your kind words!
Great tutorial, especially going through and checking all the IC pins/functions.
++Subscription
Awesome, thank you!
G'day Tony. These power supplies are great to have on hand, or at the workbench.
Very easy to modify into Variable Outputs, AC and DC, current limiting, and Isolated Outputs. (Good replacement for Commodore and Amstrad computers)
Unfortunately, Some do suffer from cheap components, usually the controller chip.
The older versions (late 80's to late 90's) are very robust.
That 👉single👈Hi Voltage Capacitor is a failure point. I would normally add a second with similar, but not the same, spec's.
Cheers.😉
Interesting, you mean the main 450V capacitor? I usually don't replace them as they are expensive and at that point you start questioning whether to invest in a repair or get a new one. Also space on that side of the board is limited. But I'll keep that in mind thanks!
Thanks for the in-depth analysis.
You're very welcome!
You might consider retesting that IC as it may have been that broken capacitor the whole time. It could also have been a cold solder joint.
Yes, very good point - I might keep it for a future repair. Though the spares were cheap and wondering if I wanted to solder and de-solder it twice risking to damage the traces... uhm... Thank you!
Agree. It was probably micro fracture and the heat was making it connect temporarily through expansion. Good video.
Very informative video, please keep the good work & Good luck.
Thank you!
With an old SMPSU, beware of dried out electrolytics that can prevent SOME psu's from starting.
ALWAYS use an IC socket when replacing an IC.
I didn’t install the socket on purpose on this occasion. There are 340V nearby, I don’t want that IC to come off for whatever reason.
Anywhere else, 100% 🙂
I think you're probably safe with parts that have silkscreened part numbers. The dodgy parts all seem to have their part numbers laser etched, probably because it's easier.
Probably yes. I'm also wondering whether it would make any sense to "fake" an SMPS controller IC? A power transistor sure, you can sell cheaper stuff for more money. But an SMPS controller? Either it doesn't work or it's genuine and works :)
@@tony359 if there was a particular SMPS controller that was widely used and popular they probably would! I guess there's a smaller selection of high power MOSFETs that are commonly used so they tend to get faked.
Good to see it worked though, another success!
@@tony359 Whether it makes sense or doesn't, someone out there does it ROUTINELY to all the salvaged circuits, taking off the top surface and repainting the manufacturing date. Perhaps they have found that when one seller sells "new" ICs and another seller sells "used" ICs, the one with the "new" ones is less likely to get stuck with inventory hogging their shelves, and they have the technology so they're going to use it.
And i disagree about lasered. My Yamaha YM3438 soundchips are definitely ones that have been remarked and they're silkscreen marked, not lasered. Yes they actually are YM3438s but they are definitely salvaged and definitely not from batch and year claimed.
we're assuming that those who are recycling those chips know what they're doing. Likely they don't. They just recycle and hope to sell.
@@SianaGearz What date code do they claim to be?
Great job, well explained, thank you.
Thank you so much!
Excellent explanation, thank you!
You're very welcome!
Learned from this well done 😊
Thank you!
Thank you for this great video! Very entertaining.
Glad you enjoyed it!
The reason is the inductive reactance of the coils of the transformer. For higher frequency you need less turns of each winding. That is why you can make it smaller.
thanks!
Thanks alot for the education,l have leart alot.Looking forward for more such explanation.
You are very welcome, thanks for watching!
Nice fix, but I think you should have also replaced the small electrolytic that does the startup supply for the IC, small caps usually die first, I’ve fixed several power supplies just by replacing the start up capacitor.
Hi Scott - I have, off camera 🙂 thanks for mentioning!
@@tony359 good stuff 👍
Very Good! Well done.
Thank you very much!
Great informative video, nice 👍
Thanks for the visit!
Symmetrical powersupplies are not only for balanced outputs. Nearly every opampcircuit needs it to function properly. You could use voltage dividers and have a so called "virtual earth", but this isn't exactly how good audio circuits should be built.
Thanks for the insight, appreciated!
Teşekkürler hocam . Emeğine sağlık.👍
Thank you!
Nice!... Great Repair! 😀
Thanks! 👍
Great video as always. Cheers!
Thanks for the visit
Hi Tony! - I follow your advice and dont mess with power supplies
Not because of the explanation you and other people give about the basics of its operation
That I understand... the big components I understand, the bridge rectifier, the switching transistors etc
But it is all that ARMY of small components there, resistors, ICs, capacitors that really scares me... it seems there is so so so much more going on there
Dont tell me all those dozens of tiny componentes are all just for the voltage sensing and feedback circuit....
oh well, I don't know that myself! :) Sometimes I feel those PCBs are designed with random "seeds" added to the PCB just to scare normal people like us :)
Thanks for watching!
Good job, very interesting!
thanks!
Excellent vid. Just wonder if the Cap was half broken and the heat was making it good and the controller might be ok? Only thing i might have done is put in a socket for a few cents and makes switching and testing out parts to narrow down a little easier and if it comes back again?
Yes that is a possibility. I intentionally soldered the IC on the PCB because it's the primary of a power supply. Call me over-cautious but there are 340V nearby :)
Those ICs are cheap, not a big deal.
Thanks for watching!
@@tony359 Yes, you are right. Normally, theres a metal barrier with the mosfets of pri and sec making it pretty safe, and i suppose a little hot glue on both sides of the chip will stop it coming out and easy to replace again if its "chinese" and not going to last long time. I had a bad controller on a tek Oscilloscope but the board was all one piece and insanely hard to get to the power section so i put in a socket there just so i could pop it out easily next time and main power was actually 42V coming from a power brick with fusing but i put my own just for added protection as a hot wire can come loose any time too flail around and short on any PS. Just found your channel and will go back and watch you old vids as very instructive. I fix (try) a lot of laptop M/B's these days but always learning so if you can do some of those, that be great too.
The truth is that if that PSU fails again, it'll likely end up in a bin I'm afraid. Shipping also can do wonders. I shipped one PSU like that years ago and it arrived at destination with the PFC transformer (I know it's not a transformer, you get what I mean) RIPPED from the board. But the metal cage was undamaged. HOW! :)
Hello Sir,please can i have the link to the shop you bought the ic?
Nice job. Enjoy your videos.
Thanks 👍
Good job, Tony!
Very informative video, Tony; I’ve just subscribed to your channel.
Keep up the good work, mate, and pay zero attention to the haters; it’s a bloody strange world online these days.
Thank you and welcome! Haters are annoying but yes, it’s a strange world indeed 🙂
Just one tiny nitpick... Although I agree I don't expect the IC to be changed on a regular basis, I would have socketed it. Then again, that does introduce another layer that *may* cause issues... So, now I'm not so sure about my own nitpick... :P
Hi - thanks for your comment! It was intentional to be honest. On anything else, by all means. On the primary of a power supply with 340V running around, I prefer to have everything soldered on the PCB :) Thanks for watching!
Good video - thank you
Thank you for watching!
Nice video thanks.
You're welcome!
If you already replacing caps - at least check the high voltage one. People often do not even check them as they're mostly good but that's more "good enough" than good after 20 years. Even with low frequency of main network transformer still stress them with high frequency depletion and sitting there in the middle of heatsinks doesn't help. They're working closer to rated voltage (sometimes just 10-30V under it) also putting additional stress on them.
Also small cap (usually 10-22uf/50V) next to control IC is common point of failure, replacing it with new quality cap is more important then replacing good measuring output capacitors.
Thank you - I ended up replacing the startup capacitor off camera just for preventive maintenance as you say. Thank you!
Tony @ 2:14 you say "it's not exactly a transformer". Could you elaborate a bit please? Is it some kind of choke then?
DJMarik78 clarified that a bit more down below. But apparently I could call that a transformer :)
@@tony359 Thank you. You gave a very thorough walk through of the trouble shooting.
Why didn't you socket that IC? It'd be a lot easier to switch back to the old one (or others) for testing like perhaps it only was that little cap…
It was intentional to be honest. It's the primary of a switching mode power supply, there is 340V nearby. I'd rather not use a socket there.
The only pin you did not measure after you got it working was the vcc, I suspect this will show you the cap is duff on VCC and you saw the ripple on VCC when it was not starting I am upto 20mins so far.
I stick by my diag, just the new IC is more tolerant.
I repair quite a lot of PSU's and the cap is the most common replacement, in fact I repaired a medical grade PSU tonight and it was a 100uf 35V on pin 7 of a 3842 IC.
I rarely replace PSU IC's unless it has blown the output FET then it usually kills the ic.
On the other hand if a TOPxxx ic is not working that is much more common.
I can measure again but the PSU is still working after many hot-cold cycles. I believe (not sure) that that amount of ripple is normal when the PSU has not started yet.
@@tony359 I assume the new ic is more tolerant of the dropping DC on VCC.
I would replace it anyway and measure the ripple on the replacement.
Curiosity getting the better of me.
I am also a curious person. I'll measure the ripple with the new IC and new capacitor (I've replaced that cap already off camera)
were can i get this digital load unit from pls. and very good video.
Search for Atorch online :) Thank you!
Can you do a tutorial on your oscilloscope since you explain very nicely and are understable
I know it’s been on my to do list for quite some time!!
To be honest the capacitors I would change automatically are the tantalum beads. They are notorious for going short circuit and, after 20 years I wouldn't trust them.
On a 1980 machine, sometimes. That's a 2004 power supply. :)
Marvelous content! I've subscribed!
Welcome aboard!
Well done
Thanks!
Dear Tony
Love Your Videos, What are you using to magnify while working and what kind of microscope do you recommend?
Thank You 🙏
Thank you! For the microscope, take a look at this: ua-cam.com/video/2Ag7E7KMR6s/v-deo.html
Why do you call that cap .1µF? I'm used to 100nF.
Likely it was broke but you did not see it, and when you heated, it heated the pad enough to move just a bit to have a gap. So the IC could possibly be fine ... who knows.
Yes that is a possibility!
nice repair, Tony, but since this is about a PSU, one question: you take 240V from the outlet and then the PSU increases it to 340V, in this case. why? why does it have to do that so the end result is just 5V, or 15V. wouldn't it be easier from 240 to 5 rather than 240 - 340 - 5?
Because you don't really have a choice - it happens automatically when you rectify mains voltage.
The mains voltage swings up and down between positive, going through zero, to negative, back to zero and then positive again in a continuous sinewave. The rectifier allows energy to flow into the smoothing capacitor as long as the mains voltage is higher than the voltage the capacitor is at. Once the sinewave goes back towards zero again at the end of the swing, the rectifier acts like a check valve and the capacitor remains charged at the highest voltage the mains hit. This repeats over and over again and keeps the capacitor charged at near the peak mains voltage which, in Europe and the UK, is around 340V(*)
*) We say the mains is 240V because that's the effective voltage, basically the "average" (not exactly - it's complicated) between all the intermediate voltage levels the sinewave goes through as it swings up and down. The peak voltage that the sinewave hits is actually 1.41 (square root of 2) times higher than that, which is where the figure of approximately 340V comes from.
Thanks - Sorry I didn't explain that. It's just what you get when you rectify 240V AC to DC via bridge rectifier and smoothing capacitor. It's inevitable unfortunately :)
Mains is using high voltage to minimise loss due to higher currents: Voltage and Currents are linked when it comes to power. So to transfer a certain amount of power from A to B you can either use high voltage and low currents (small wires) or low voltage but high current (big wires and big losses).
Here in the UK, we use 110V in building sites where accidents are more likely. We have 110V tools for that purpose only. It won't be safe but it's... safer - actually it's "less dangerous" :)
@@tony359 ty, Tony!
@@ELHV ty, ELHV
240V is RMS voltage. After you rectify the voltage and charge a capacitor you have peak voltage. Which is going to be RMS times 1.414 or 339.36 VDC. Minus the voltage drop of 2 diodes in the bridge. But let's not get too technical. A sine wave is up and down and RMS is 0.707 of the peak reading. So when the cap bulks the wave up you get close to peak voltage. Or you can just chalk it up to magic and call it a day too.
Auto translation says "little voltages" instead "lethal" voltages.
Thanks - it’s done by Resolve but I only do a spell check. I’ll amend!
Me: "I'm bored, I don't know what to watch..."
Tony: "How about me fixing a power supply?"
Me: "Son of a gun, I'm in!" >> clicks like, proceeds to watch
ahah thanks!
IMHO, 20 year old power devices should automatically get all its solder joints redone.
I did that too! :)
It could have been a bad solder joint👍
Yes, it could have been!
Seems that you have a cold solder joint
maybe! :)
Those tanalum caps really are troublesome and should be changed out!
This is not a 40 years old IBM motherboard :)
Good morning…, great video, and well explained. My recommendation is to slow down slightly in your explanation. It’ll help those in learning the hobby. Kindest regards!
Thank you - I do appreciate your feedback and the time you've invested to let me know.
I noticed you keep saying 'cage'. Out of curiosity: is that a common thing? I'm not an native english speaker but isn't "housing" a better word for it? Enjoyed the video nonetheless Tony! Always do! Keep up the good work!
Housing sounds good - cage might be less accurate indeed. I have said much worse things on this channel when it comes to English :) Thanks for watching!
So maybe chip was good, but cracked capacitor was a problem ?
maybe :)
They find fault and then cook it more. Glad I fix my own equipment. God it's getting worse...
who is "they"?
Good video. 3,2,1 Go! ;)
Genius !!
for so little! :) Thanks!
It could have been a dry joint
Of course!
Hilarious auto caption fail 0:13 - "there are little voltages inside" :)
thanks - I had forgotten to amend it! It's fixed now! :)
Can I send you fifty Optiplex 780 and 790 bad PSU’s to fix? ❤ I’ll just buy one for now 😅
No! 😅 But I think the optiplex are infamous for being affected by the capacitor plague so it might be an easy fix. Be careful though :)
❤❤❤
как же круто когда ты можешь смотреть видео на 4 языках. poti sa treci in romina. Украинску мову. and english... Its time to learn one more.
I can add some Italian...
@@tony359 considering that Romanian is a distant relative of Italian... if they don't speak it too fast I'll understand the meaning, but not the whole text.😅
Romans :) (as in Ancient Rome!)
First isense Test on the Right Side of the Chip. Second isense Test on the left Side? WTF? Did i miss something?
I might have mixed up the names, I need to double check!
I might have mixed up the names, I need to double check!
The actual fault could have been a bad solder joint or the cap that broke during de-soldering. From a 35 min video I expected some more in depth analysis, instead of just replacing a part and be done with it.
You are right - it's hard to say.
I'm curious: I've scoped the IC before and after, explained how an SMPS works, what kind of "in depth analysis" were you expecting? I'm just asking, not challenging.
@@tony359 I would have proceeded in the following order: 1) re-flow all solder joints 2) replace the broken cap 3) replace the IC, and checked functionality between those steps That is from simple to complex, and that would have identified the actual problem. By replacing the IC and the cap without checking functionality in between you never know unless you do some further analysis, for example put the old IC back in.
Yes, I could have replaced that cap and check - but does that qualify as "lack of in depth analysis"?
I noticed the cap was broken AFTER I de-soldered the IC. Re-solder the IC and - potentially - having to de-solder it again will have probably caused some damage on those small traces - sockets are not an option on an SMPS in my opinion.
The only thing I couldn't pinpoint 100% is whether the issue was the cap or the IC.
@@tony359 For a 35 min YT video I would have put the first IC back again, just for the sake of being able to arrive at a definitive conclusion.
@@mojoblues66 sure but as I said, soldering-desoldering an IC on that PCB will eventually cause some damage. Particularly if I had soldered it back and ascertained it was indeed faulty, so more soldering would be required.
All caps are junk after 10 years so what do you do😮😮😮
no they're not :)
Size of components has nothing to do with signal frequency in this context. Switching power supply works on a principle of controlled collapsing of magnetic field in transformer which causes a flow of vast amounts of energy through output circuit. Timing of this magnetic field fluctuations is controlled by an optically isolated feedback loop in order to minimize risk of high voltage appearing on the secondary side. That's like 80% of theory of switching supply operation. Trying to fix such a PSU with so little knowledge of schema and functions performed by its components ends just like here - a lot of missed conjectures and surprises. Not a good material to educate people, to be honest.
Thank for your comment - though I'm not sure the frequency has nothing to do with size. Would you be so kind to tell me where I said that I am trying to educate people here?
I know it's your style, and it's fine, but you don't need the 3-2-1-go countdown. we can pause and rewind, no problem
Ahah - it’s like asking Adrian not to say ‘it frikking works’ 🙂
dc transfomer...
Everybody cares. This is not crap
Hello Sir, can you repair my DC power supply? I send you an @ already.