After watching this it encouraged me to have a go at fixing my 12 volt to 240 volt inverter that had been lying around in my cupboard. When I connected the battery after I had finished it exploded spectacularly, like a firework, but at least I learnt a few things. Enjoy all you videos
This is the result of the generator having a total harmonic distortion (THD) of greater than 5%. Many small generators have a THD of greater than 20%. In general inverter generators have very low THDs and alone are safe for use with computers or other equipment using a switch-mode power supply. Excellent diagnostic and repair work, as always. Thanks.
Small tip - when testing fuses always check it by way of the contacts of the holder that the fuse is fitted into - I say this as sometimes the fuse may not be making good contact with the holder at one or even both ends, usually because of some corrosion that can't be seen.
I really liked your logical explanation as you investigated the circuit. One recommendation though - When you are measuring voltages at various IC pins, please IDENTIFY which pin number you are on. Yes, I was able to do so, but it is quicker to keep up with you, if you mention the pin number. I really appreciate your attention to detail, and keep learning from you. Many thanks, 73
A couple notes: Indeed, when using a DMM diode test on MOSFETs, I always make the verification twice - altering the polarity of the test leads. The diode test on most DMMs provides about 2.5 V and the gates are very low leakage, so a modern N-channel device (like IRF450) gate “remembers” the test voltage (+2.5 V or -2.5 V) for several seconds, maybe minutes. When you next measure the Drain to Source, you find either a short after positive, or open after negative charge, respectively. P-channel devices, like IRF9450 of course behave in the opposite way. I have used this for years in my MOSFET testing, but just recently bought one of those component identifying/testing devices that you used. Good to keep that in my mind! Another thing I noticed is that your board evidently does not have conformal coating, as you make your probing so readily. A conformal coating is a real pain for any probing. Using sharp pin extenders on the probes may help a little. On the other hand, I have seen, how an unprotected board looked when coming back from a Gulf Coast site after a hurricane. Talk about salt mist exposure! Keep on producing your educational videos….
Loved the Disclaimer. Great video and I like the way you guide us through the process from start to finish, keep up the good work and looking forward to seeing more
I got a very fancy Pioneer XM-72 receiver at a Repair Cafe and the switching chip (with built in MOSFET) had blown its top off. Nothing we could do there, but I later found a schematic, contacted the owner and he bought a couple of the ICE3BR0665J on eBay. When he brought it to the next cafe, I swapped that chip, and also two small (3216) SMD current sense resistors, and two diodes in the bridge rectifier, and finally the fuse, and it powered up first time.
I have a repair e-bike with a led acid 36v charger that went BANG when I plugged it in. I looked at it for a while and thought nah then Dropped it in the bin. I wish I could have fixed it but my skills aren’t quite there. Still fun watching you fix stuff although you should add your time into the end calculations. It may only be a cheap part but your skill is not free to people who don’t have a repair caffe. I’ll go looking for a charger on eBay and get some faulty crap I’m sure 🤠
Yes, if I was a repair business it probably wouldn't be worth spending lots of time on devices, but I only do this as a hobby and I make a small amount from UA-cam which helps go towards the bills. I think a replacement charger (used) is around £80 or so. Yes it's fun fixing stuff too. I try to do a wide range of devices so people can hopefully learn how to fix their device of, or a get some pointers on how to troubleshoot or repair a similar device 🙂 It's a shame you binned your charger as you could have sent me some photos of the board and I might have been able to give you some pointers on what to check. A bang usually means blown MOSFETS, mains fuse, possibly bridge rectifier and switching IC etc. You'll get to see pretty much all of that in the next video out Saturday!
@@BuyitFixit well it wasn’t a fuse as I checked them. As it hovered over the bin in my hand I thought about how costly a mistake could be and let it drop. I’m happy playing around with low voltage stuff but as this was 240v a little knowledge could be a dangerous thing. I’m a careful kind of guy as a machinist and I know where not to put my fingers. Not so knowledgeable around 240v. I have watched electricians work and just quietly taken a step back when I see them working on live wires while standing on an aluminium ladder. :) Thanks for your kind offer of looking at a photo. I did bin it before UA-cam decided to show me your channel. I need to buy about $150 worth of batteries and a charger before I can tell it the bike will work. At least it’s all 36v on the bike. The bike was a freebe from a friend of a friend and I have the mechanical pedal part all working again. Maybe I’ll make a restore video on it.
As soon as you said generator, my internal warning siren was going Danger Will Robinson Danger........ Tip, those heavy resistors, i'd rework those joints. Another tip, one recommended to me after working on very very expensive power supplies, put heat shrink on the pins of your probes, right down to about 2mm from the tip. We used to make our own hi precision probes, soldering a pin into a 4mm banana socket, wrap it back with heatshrink, so the tips mega sharp. Great work bud.
That area of burnt PC board, just above the output area, and corresponding to the two green resistors on the other side was screaming at me! What was that all about? (if you can still remember) Thank you for a very nice explanatory repair!
Sorry for the late reply. I just had a look back at the video, and I can't remember. I think current limiting perhaps? And thanks for the nice comment :)
I noticed you don't mention the charcoal briquettes that seem to be two power resistors, and I have to say I was more than a little bit worried about how many times those AC power leads got twisted around. Other than that very healthy fault finding techniques used
Thanks👍, I tested those resistors and they did show some resistance. The problem is that I don't have a circuit diagram so without knowing the correct values to replace them it was just assume they are OK and leave as is.
Well done on the repair. The resistors may also be for balancing (voltages across capacitors effectively in series), so may be worth rechecking capacitor voltages / resistor values (though with no oscillator running there are likely to be strange readings). Also well done on volunteering at a repair cafe, especially if that's the type where the customer can watch your every move.
Thanks Ralph. Yes customers can stay and chat. I was looking at an electric fence energiser and talking to the lady who had a couple of horses. Unfortunately couldn't repair that one as water had gotten in and corroded a lot of vias on the pcb.
With no Vref I thought there must be something like 431 ref ! clearly not and I thought it was an input..great repair, lots of people get scared when you mention SMPS and they used to bother me but if you take a bit of time the mystery out of it I bet you've fixed hundreds !...cheers.
Thanks AndyMouse, I actually haven't repaired that many SMPS. A few years back I bought a really expensive PCR machine, that had a SMPS built in, and it had around 3 logic chips that controlled the oscillation that had failed. I repaired it and got it working. It would have made an interesting video if I had been doing them at the time.
Great fault finding, not quite as great as your disclaimer 😂 I was sure it was going to be the big burnt looking resistors on the output! So how did you know the Vref is generated internal to the chip? Was it stated in the spec sheet or is this just common knowledge. Thanks Mick 👌
Once again a great video, very informative. I repair PSU's for a living and come across many with those SG3525 fitted, they seem to be a common failure
lol you needed to run that disclaimer longer. I had to pause it to read it all to the end. I do just happen to be over 206 yrs old. That whole thing reminds me of Monty Python and the Holy Grail lol
Someone else has mentioned I think on one of your other videos, that, with a Fluke meter that has gone into standby, just press the yellow 2nd function button (and possibly any of the other buttons too) and the meter will spring to life again. You don't have to turn off and turn on again..
Yes much simpler, I look at one of those (very old and had a stack of plates for the rectifier) a few weeks back at our local repair cafe. Although the switch modes do have a few advantages being more efficient and capable of delivering more current with less weight and cost.
Was interested in this as I have a HP monitor 2009v that is dead and suspect the power supply. Tried to get one on line but no luck. It has ran for 14 years then just suddenly stopped. Tried to get Circuit. I have been aware of SMPS for many years but never knew how they worked. At 73 I do now. Thank you. In the meantime I got an LG monitor from CEX. The boards in the HP do not show the heating marks yours did and it looks like the switching chip has got warm on yours. I can now have another play. 😍😍
Thanks for the offer. I have now reached the stage where i understanding all the sections of the smps for the HP 2009v. It has three daughter boards. The largest is the driver board for the CCFL TUBES. The next is the 3 watt class D amp for audio and finally the smallest being the trigger board for the switching MOSFET. Its odd that the power on button goes via the video board. Anyway I am enjoying this project of discovery and it is interesting to note how identical all the smps are. I will now start to draw it up and get and hopefully get something to UA-cam. Our brothers on the indian sub-contenant do loads on YT. Sadly it is not in my language. Now here is an AI task Google. Build a speach translator.
Those poor output resistors look like they have been pretty cooked. Also some evidence of excessive heat right by the chip the failed, possibly a contributing factor. Good vid, I don't normally get so deep into an issue like that before I just give up. I might take a look at my Peter Chou arcade SMPS that failed about 20 years ago, but I've kept around just in case.
The schematic shown at 9:57 is a half bridge, not push-pull as it is labeled. The converter on the bench is clearly a half-bridge. (Half bridge uses the "centre tapped" DC supply; push-pull uses a centre tapped primary on the transformer)
Yes, it was a soldered link inside the Milwaukee chargers as I bought a 110v one that was broken and thought it must me a universal input 110-240 as the circuit was identical to my 240v one. After plugging it in and the capacitors getting rather hot.. I noticed a small wire link marked J1 half hidden under the glue, so I replaced the caps and removed the jumper so it's now 240v. This was a 6 way charger and the label had been removed so I couldn't see the input voltage rating.
Sorry about that, I should have included it in the video (I normally do these days) I can't be 100% but a UC3825 seems familiar and has the same pinout.
@BuyitFixit Thanks! I was looking at some photos of other KT12SM boards and they seem to have the SG3525(A) chip but same idea by the looks of it. Thanks again! Love your work and logic!
I know this comment is very late, but I recommend using a series lamp, if it just lights up for second , u know that the input circuit works, if it shorts out and fully turns on then its at fault, or if its not taking power. On the other hand its the circuit after the transformer which is at fault. It just greatly reduces the time to diagnose which part of the board is faulty
Thanks 👍yes a few other people mentioned about using a dim bulb tester, I should really get round to making one. I haven't got any incandescent bulbs lying around, I'll have to see if there are any available still.
I used to work as a EE. In a business 🎉🎉machines co back in the 60/70 ‘s fixing large copiers/ printers etc and had loads of trouble with smpsu’s motor control boards! Inrush currents at switch on was very common which took out diods, drive transistors etc! After much trouble with this fitting a 60 watt bulb + a delay relay cured the problem completely!
Varistors never lasted as the machines were very current hungry taking 10 + amps at switch on! The bulbs were still working 5-10 years later! Nowadays they are powered all the time in sleep mode and at startup motors are time delayed in a controlled fashion! The simple 60 Watt bulb saved the day!😅
@@BuyitFixitfilament oven lamps are still available. Amazingly the politicians understood that plastic LEDs wouldn't be good at 240°C I still have pre-halogen 40/60/100W bulbs. I stockpiled and often got them on clearance as the ban approached 😉
Never wise to run electronic devices on standard generators - the THD can do all sorts of damage. I always use an inverter generator for TV's, PC's etc. Worth mentioning to your PSU owner.
I've got an expensive tagan 550w pc psu that's just turned a hard drive to a burn on my desk and now all rails read high on my psu tester, any interest to you?
You say the discharge resistors prevent you getting a shock from touching the board but would I be right in thinking their actual purpose is to prevent a shock from unplugging the device and touching the prongs of the plug because of energised caps?
wheres the local repair cafe ive never heard of one before, are you in the north east i live in sunderland and i wonder if theres one near me. how does it work can you take something in to see if it can be fixed and do they have set charges. sorry for all the questions but the repair cafe sounds like a great idea
I'm not sure about Sunderland I'm in Cumbria. Yes people just bring stuff in for repair and either pay for parts if required or give a donation. I'm currently at the local one that's held once a month as I'm typing this! With a LG tv in bits next to me :)
Louise Rossman has started a similar thing but he allows people to repair things themselves with supervision from knowledgable people. I’d love a repair cafe or similar in Sunderland or the surrounding area, I have a small channel and repair things with my limited knowledge but would love to learn more and repair a larger variety of equipment. It also helps others and keeps otherwise good products out of landfill
Exactly. I've repaired stuff for years. I remember getting a 50" plasma from the local tip for £30 and fixing it for £20. A plasma tv were about £1000 at the time!
Yes, I think it's the resistors for current limiting the charge output. Someone asked me if I would have a look at a similar one, and sent me some pictures. It too has similar scorch marks.
My father owns a vacuum cleaner Polti (model Lecologico) and it powers on but nothing happens when pressing the Start button. The motor works when applying power, the switches and cables are OK, replaced all caps and triac, don't see any damage on the pcb nor cracked joints. The main chip has nothing written on it, zero. It's an old model and sent an email to Polti telling my troubleshooting and asking for schematics, which they replied "No". Now what do I do next? Thx
It's hard to say without having ever seen one. What is the PCB for? Could you bypass it perhaps with a simple switch? If it has a "main chip" is it getting power? getting hot? that might be something to check.
Noise on the input? Frequency not right if they switched off the generator while it was plugged in? Could be a number of things or possibly not even related to the generator.
It's a place where people bring bring their broken items, and people volunteer to be repairers. It's pretty much like a local community charity type thing. I think they are quite big over in Germany. There's quite a few in the UK too from a quick google search. Also people can donate broken things, which are then repaired and donated, or recycled.
@@BuyitFixit very un American now lol. The mass consumption here won't allow such a wonderful thing to take place. Well with how things are going we too will have to start these up . Thanks!
Yes correct. It's been a while since I looked at this i can't remember if it was just floating or went through a weak pullup resistor or had an internal pullup.
@@BuyitFixit Ok. You measured it at 0V so that was a bit weird. The chip must have been bad either way as the board started working once you replaced the chip! Just thought you might have paused for consideration when you measured 0V there!
Yep chip was bad, from memory I think the datasheet said it had an internal pullup connected to vref, so it should have measured a voltage even when not connected to anything which is why I knew it was the chip. Thanks for commenting 👍🙂
@@BuyitFixit It's interesting feedback, some people will know how to break down and diagnose an iphone fault, others won't know which end of a hammer to hold! You seem to be doing something right!
smps are a joke. pocket size unreliable and expensive to get repaired. Add to that all those other components to make it work. So apart from the weight, what is the point?
Cost and size and efficiency. Copper is expensive. You would need a huge copper transformer at mains frequency to do the same job and waste a lot if heat. That's why they up the frequency.
@@BuyitFixit Not very efficient if they keep busting are they! So are you saying all those extra add ons like transistors capacitors, resistors they make come free do they? Great if that's the case... free energy :)
No, not free, just cheaper than a huge lump of copper. And as you say, a lot more complex and probably more unreliable than an old linear power supply.
Thanks, I've not heard of these before. I think the only time I've really used a scoop in XY was years back when adjusting laser disc players 😂I'll have a look into what you suggested 👍
After watching this it encouraged me to have a go at fixing my 12 volt to 240 volt inverter that had been lying around in my cupboard. When I connected the battery after I had finished it exploded spectacularly, like a firework, but at least I learnt a few things. Enjoy all you videos
Thanks Ewan. I've actually bought a faulty 600w inverter to do a future video on...
This is the result of the generator having a total harmonic distortion (THD) of greater than 5%. Many small generators have a THD of greater than 20%. In general inverter generators have very low THDs and alone are safe for use with computers or other equipment using a switch-mode power supply. Excellent diagnostic and repair work, as always. Thanks.
Thanks for that, and for the info 👍
Small tip - when testing fuses always check it by way of the contacts of the holder that the fuse is fitted into - I say this as sometimes the fuse may not be making good contact with the holder at one or even both ends, usually because of some corrosion that can't be seen.
Thanks M Jons. I've had that before with blade fuses especially in cars!
great simple tip. Thank you
I have seen fuses blocked by a simple strand of hair
That being said if there was a short and you metered continuity the fuse could still be blown
Good save. I was staring to feel like Mrs. Doubtfire there for a while. You have been awarded 🎓🎓🎓🎓🎓 Smarty I.T. awards.
😂😂😂Thanks 👍
Wish I knew more about how to diagnose and repair these boards. Thanks for sharing👍
And thank you also for commenting and liking!
I really liked your logical explanation as you investigated the circuit. One recommendation though - When you are measuring voltages at various IC pins, please IDENTIFY which pin number you are on. Yes, I was able to do so, but it is quicker to keep up with you, if you mention the pin number. I really appreciate your attention to detail, and keep learning from you. Many thanks, 73
Thank you I'll try to remember that in the future!
A couple notes: Indeed, when using a DMM diode test on MOSFETs, I always make the verification twice - altering the polarity of the test leads. The diode test on most DMMs provides about 2.5 V and the gates are very low leakage, so a modern N-channel device (like IRF450) gate “remembers” the test voltage (+2.5 V or -2.5 V) for several seconds, maybe minutes. When you next measure the Drain to Source, you find either a short after positive, or open after negative charge, respectively. P-channel devices, like IRF9450 of course behave in the opposite way. I have used this for years in my MOSFET testing, but just recently bought one of those component identifying/testing devices that you used. Good to keep that in my mind!
Another thing I noticed is that your board evidently does not have conformal coating, as you make your probing so readily. A conformal coating is a real pain for any probing. Using sharp pin extenders on the probes may help a little. On the other hand, I have seen, how an unprotected board looked when coming back from a Gulf Coast site after a hurricane. Talk about salt mist exposure! Keep on producing your educational videos….
Thanks, and thanks for the tips 👍
Loved the Disclaimer. Great video and I like the way you guide us through the process from start to finish, keep up the good work and looking forward to seeing more
Thanks Morten! Glad you enjoyed it! Yes I thought I'd try add a bit humor and see if anyone noticed :)
I got a very fancy Pioneer XM-72 receiver at a Repair Cafe and the switching chip (with built in MOSFET) had blown its top off. Nothing we could do there, but I later found a schematic, contacted the owner and he bought a couple of the ICE3BR0665J on eBay. When he brought it to the next cafe, I swapped that chip, and also two small (3216) SMD current sense resistors, and two diodes in the bridge rectifier, and finally the fuse, and it powered up first time.
@@gadgetmind Very Nice. Well done and especially for going the extra mile on that one 👍
I have a repair e-bike with a led acid 36v charger that went BANG when I plugged it in.
I looked at it for a while and thought nah then Dropped it in the bin.
I wish I could have fixed it but my skills aren’t quite there.
Still fun watching you fix stuff although you should add your time into the end calculations. It may only be a cheap part but your skill is not free to people who don’t have a repair caffe. I’ll go looking for a charger on eBay and get some faulty crap I’m sure 🤠
Yes, if I was a repair business it probably wouldn't be worth spending lots of time on devices, but I only do this as a hobby and I make a small amount from UA-cam which helps go towards the bills. I think a replacement charger (used) is around £80 or so. Yes it's fun fixing stuff too. I try to do a wide range of devices so people can hopefully learn how to fix their device of, or a get some pointers on how to troubleshoot or repair a similar device 🙂 It's a shame you binned your charger as you could have sent me some photos of the board and I might have been able to give you some pointers on what to check. A bang usually means blown MOSFETS, mains fuse, possibly bridge rectifier and switching IC etc. You'll get to see pretty much all of that in the next video out Saturday!
@@BuyitFixit well it wasn’t a fuse as I checked them. As it hovered over the bin in my hand I thought about how costly a mistake could be and let it drop.
I’m happy playing around with low voltage stuff but as this was 240v a little knowledge could be a dangerous thing.
I’m a careful kind of guy as a machinist and I know where not to put my fingers. Not so knowledgeable around 240v.
I have watched electricians work and just quietly taken a step back when I see them working on live wires while standing on an aluminium ladder. :)
Thanks for your kind offer of looking at a photo. I did bin it before UA-cam decided to show me your channel.
I need to buy about $150 worth of batteries and a charger before I can tell it the bike will work. At least it’s all 36v on the bike.
The bike was a freebe from a friend of a friend and I have the mechanical pedal part all working again. Maybe I’ll make a restore video on it.
Blimey Mick, I've not heard the term Schottky Diode for 30 years! 😃 Nor seen a solder sucker for nearly as long. 😊
The solder sucker still comes in handy 🙂👍
The best fine print that I have read in it's entirety! Of course it's the only one for good reason
😂😂😂😂
Heya, yes love these kind of repair
Thanks 👍
As soon as you said generator, my internal warning siren was going Danger Will Robinson Danger........
Tip, those heavy resistors, i'd rework those joints.
Another tip, one recommended to me after working on very very expensive power supplies, put heat shrink on the pins of your probes, right down to about 2mm from the tip. We used to make our own hi precision probes, soldering a pin into a 4mm banana socket, wrap it back with heatshrink, so the tips mega sharp.
Great work bud.
Thanks Simon, and thanks for the tips. Great idea on putting heat shrink on the probes 👍
Good fault finding very logical
Thanks Roy 👍
That area of burnt PC board, just above the output area, and corresponding to the two green resistors on the other side was screaming at me! What was that all about? (if you can still remember) Thank you for a very nice explanatory repair!
Sorry for the late reply. I just had a look back at the video, and I can't remember. I think current limiting perhaps? And thanks for the nice comment :)
cool description of SMPS.
Thanks chillywilly 👍
I noticed you don't mention the charcoal briquettes that seem to be two power resistors, and I have to say I was more than a little bit worried about how many times those AC power leads got twisted around. Other than that very healthy fault finding techniques used
Thanks👍, I tested those resistors and they did show some resistance. The problem is that I don't have a circuit diagram so without knowing the correct values to replace them it was just assume they are OK and leave as is.
Well done on the repair. The resistors may also be for balancing (voltages across capacitors effectively in series), so may be worth rechecking capacitor voltages / resistor values (though with no oscillator running there are likely to be strange readings). Also well done on volunteering at a repair cafe, especially if that's the type where the customer can watch your every move.
Thanks Ralph. Yes customers can stay and chat. I was looking at an electric fence energiser and talking to the lady who had a couple of horses. Unfortunately couldn't repair that one as water had gotten in and corroded a lot of vias on the pcb.
With no Vref I thought there must be something like 431 ref ! clearly not and I thought it was an input..great repair, lots of people get scared when you mention SMPS and they used to bother me but if you take a bit of time the mystery out of it I bet you've fixed hundreds !...cheers.
Thanks AndyMouse, I actually haven't repaired that many SMPS. A few years back I bought a really expensive PCR machine, that had a SMPS built in, and it had around 3 logic chips that controlled the oscillation that had failed. I repaired it and got it working. It would have made an interesting video if I had been doing them at the time.
Cracking fault finding 😊👍👍
Thanks 👍🙂
Great fault finding, not quite as great as your disclaimer 😂 I was sure it was going to be the big burnt looking resistors on the output! So how did you know the Vref is generated internal to the chip? Was it stated in the spec sheet or is this just common knowledge. Thanks Mick 👌
Thanks Vince 👍 Did you read the disclaimer all the way to the end? 😂😂😂. Yes on the datasheet it said the chip provided the Vref internally.
@@BuyitFixit I did, luckily my eyesight is still good 😂 It was good to see the missing voltage to prove the chip had failed internally 👌
😂😂 Thanks Vince!👍👍
Once again a great video, very informative. I repair PSU's for a living and come across many with those SG3525 fitted, they seem to be a common failure
Thanks Ian 👍🙂
lol you needed to run that disclaimer longer. I had to pause it to read it all to the end. I do just happen to be over 206 yrs old. That whole thing reminds me of Monty Python and the Holy Grail lol
But.. do you have a Goat? I was actually wondering if anyone would pause it and read it :)
@@BuyitFixit i dont own a goat. Yet.
@@wherami lol
@@BuyitFixit Remarkably, I have scary good eyesight, even with the video on inset mode!
Well done! :)
Someone else has mentioned I think on one of your other videos, that, with a Fluke meter that has gone into standby, just press the yellow 2nd function button (and possibly any of the other buttons too) and the meter will spring to life again. You don't have to turn off and turn on again..
Yes, Thanks for that. I've been doing that in recent videos since it was mentioned 👍
Very easy to follow,
Cheers 👍
How much simpler was an old school linear battery charger. Just a transformer and rectifier. So much less to go wrong.
Yes much simpler, I look at one of those (very old and had a stack of plates for the rectifier) a few weeks back at our local repair cafe. Although the switch modes do have a few advantages being more efficient and capable of delivering more current with less weight and cost.
Another great helpful video. thank you
Glad it was helpful 👍
Great job , mate.
Thanks 👍
wonderful repair!
Thanks j s!
Was interested in this as I have a HP monitor 2009v that is dead and suspect the power supply. Tried to get one on line but no luck. It has ran for 14 years then just suddenly stopped. Tried to get Circuit. I have been aware of SMPS for many years but never knew how they worked. At 73 I do now. Thank you. In the meantime I got an LG monitor from CEX. The boards in the HP do not show the heating marks yours did and it looks like the switching chip has got warm on yours. I can now have another play. 😍😍
Thanks, if you get stuck feel free to drop me a message 👍
Thanks for the offer. I have now reached the stage where i understanding all the sections of the smps for the HP 2009v. It has three daughter boards. The largest is the driver board for the CCFL TUBES. The next is the 3 watt class D amp for audio and finally the smallest being the trigger board for the switching MOSFET. Its odd that the power on button goes via the video board. Anyway I am enjoying this project of discovery and it is interesting to note how identical all the smps are. I will now start to draw it up and get and hopefully get something to UA-cam. Our brothers on the indian sub-contenant do loads on YT. Sadly it is not in my language. Now here is an AI task Google. Build a speach translator.
Those poor output resistors look like they have been pretty cooked. Also some evidence of excessive heat right by the chip the failed, possibly a contributing factor.
Good vid, I don't normally get so deep into an issue like that before I just give up. I might take a look at my Peter Chou arcade SMPS that failed about 20 years ago, but I've kept around just in case.
Thanks Bob, yes I thought the resistors might have been the problem but they measured ok. Good luck with your arcade PSU 👍
Well done
Thanks 👍
The schematic shown at 9:57 is a half bridge, not push-pull as it is labeled.
The converter on the bench is clearly a half-bridge.
(Half bridge uses the "centre tapped" DC supply; push-pull uses a centre tapped primary on the transformer)
Thanks for that Doug, it's something that I didn't know. I'm not an expert so I do get things wrong 😊👍
The 2 series filter capacitors form a doubler on 110v input by jumpering the center tap to ac rail going to the bridge rectifier
Interesting. I missed that. It sounds very similar to what then Milwaukee fast changer has that I recently looked at.
@@BuyitFixit that's all the 115/230v switch on cheap at psu's do
Yes, it was a soldered link inside the Milwaukee chargers as I bought a 110v one that was broken and thought it must me a universal input 110-240 as the circuit was identical to my 240v one. After plugging it in and the capacitors getting rather hot.. I noticed a small wire link marked J1 half hidden under the glue, so I replaced the caps and removed the jumper so it's now 240v. This was a 6 way charger and the label had been removed so I couldn't see the input voltage rating.
Brill video nice simple explanation of a switch mode p/s.
Thanks Mike!
Great video! I'm hard of hearing and the cc isn't picking up certain things:
What was the part number of the faulty chip?
Sorry about that, I should have included it in the video (I normally do these days) I can't be 100% but a UC3825 seems familiar and has the same pinout.
@BuyitFixit Thanks! I was looking at some photos of other KT12SM boards and they seem to have the SG3525(A) chip but same idea by the looks of it.
Thanks again! Love your work and logic!
I know this comment is very late, but I recommend using a series lamp, if it just lights up for second , u know that the input circuit works, if it shorts out and fully turns on then its at fault, or if its not taking power. On the other hand its the circuit after the transformer which is at fault. It just greatly reduces the time to diagnose which part of the board is faulty
Thanks 👍yes a few other people mentioned about using a dim bulb tester, I should really get round to making one. I haven't got any incandescent bulbs lying around, I'll have to see if there are any available still.
I used to work as a EE. In a business 🎉🎉machines co back in the 60/70 ‘s fixing large copiers/ printers etc and had loads of trouble with smpsu’s motor control boards! Inrush currents at switch on was very common which took out diods, drive transistors etc! After much trouble with this fitting a 60 watt bulb + a delay relay cured the problem completely!
Varistors never lasted as the machines were very current hungry taking 10 + amps at switch on! The bulbs were still working 5-10 years later! Nowadays they are powered all the time in sleep mode and at startup motors are time delayed in a controlled fashion! The simple 60 Watt bulb saved the day!😅
Great ingenuity 👍
@@BuyitFixitfilament oven lamps are still available. Amazingly the politicians understood that plastic LEDs wouldn't be good at 240°C
I still have pre-halogen 40/60/100W bulbs. I stockpiled and often got them on clearance as the ban approached 😉
Never wise to run electronic devices on standard generators - the THD can do all sorts of damage. I always use an inverter generator for TV's, PC's etc. Worth mentioning to your PSU owner.
Thanks for that 👍I think he's learned his lesson 🙂
😂😂😂 best disclaimer off all time 👍👌👏
😂😂😂😂👍
I've got an expensive tagan 550w pc psu that's just turned a hard drive to a burn on my desk and now all rails read high on my psu tester, any interest to you?
If you was unsure about 5 Volts on pin 1 being there, you could of desolded pin 1 and checked the voltage
CHEERS Another top video pal keep it up
Thanks Lee! 👍👍👍
@@BuyitFixit your welcome bud, thanks 4 the videos keep um commin
You say the discharge resistors prevent you getting a shock from touching the board but would I be right in thinking their actual purpose is to prevent a shock from unplugging the device and touching the prongs of the plug because of energised caps?
Hi Steve, the voltage from the caps wouldn't be able to do that because of the diodes in the bridge rectifier would prevent voltage flowing back.
@@BuyitFixit ahhh, yes, doh!
wheres the local repair cafe ive never heard of one before, are you in the north east i live in sunderland and i wonder if theres one near me. how does it work can you take something in to see if it can be fixed and do they have set charges. sorry for all the questions but the repair cafe sounds like a great idea
I'm not sure about Sunderland I'm in Cumbria. Yes people just bring stuff in for repair and either pay for parts if required or give a donation. I'm currently at the local one that's held once a month as I'm typing this! With a LG tv in bits next to me :)
@@BuyitFixit you need to move to sunderland and start one up here haha
Louise Rossman has started a similar thing but he allows people to repair things themselves with supervision from knowledgable people. I’d love a repair cafe or similar in Sunderland or the surrounding area, I have a small channel and repair things with my limited knowledge but would love to learn more and repair a larger variety of equipment. It also helps others and keeps otherwise good products out of landfill
Exactly. I've repaired stuff for years. I remember getting a 50" plasma from the local tip for £30 and fixing it for £20. A plasma tv were about £1000 at the time!
Looking at the state of the board that looks like it got really hot you can see parts of it scorched😮😮😮
Yes, I think it's the resistors for current limiting the charge output. Someone asked me if I would have a look at a similar one, and sent me some pictures. It too has similar scorch marks.
Awesome 👍🏻👍🏻👍🏻✌🏻✌🏻✌🏻
Thanks Bhushan!
My father owns a vacuum cleaner Polti (model Lecologico) and it powers on but nothing happens when pressing the Start button. The motor works when applying power, the switches and cables are OK, replaced all caps and triac, don't see any damage on the pcb nor cracked joints. The main chip has nothing written on it, zero. It's an old model and sent an email to Polti telling my troubleshooting and asking for schematics, which they replied "No". Now what do I do next? Thx
It's hard to say without having ever seen one. What is the PCB for? Could you bypass it perhaps with a simple switch? If it has a "main chip" is it getting power? getting hot? that might be something to check.
8:03 gated, meter provides enough to gate them , slow avalanche
How many amps can this handle?
I just did a quick search and found a picture of the same model. It says on the label maximum current 12A.
Too much time since , but any ideas how plugging into generator - would make it fail ?
Thanks agian
Noise on the input? Frequency not right if they switched off the generator while it was plugged in? Could be a number of things or possibly not even related to the generator.
whats a local repair cafe? never heard of something like that
It's a place where people bring bring their broken items, and people volunteer to be repairers. It's pretty much like a local community charity type thing. I think they are quite big over in Germany. There's quite a few in the UK too from a quick google search. Also people can donate broken things, which are then repaired and donated, or recycled.
@@BuyitFixit very un American now lol. The mass consumption here won't allow such a wonderful thing to take place. Well with how things are going we too will have to start these up . Thanks!
Switch mode power supply battery. Charger repair. KT2SM.
Did you notice the burnt out compont?
If you mean the resistor it wasn't burnt out. The board was just discoloured from the heat from it.
Please let me ask,the sg3525 is a pwm control circuits,could you check the output signal with a scope?
You could, but you would need to use an isolation transformer, or perhaps a portable scope, as you would need a common ground.
An active low Shutdown pin. Doesn't that mean that 0V on that pin means that it is in shutdown?
Yes correct. It's been a while since I looked at this i can't remember if it was just floating or went through a weak pullup resistor or had an internal pullup.
@@BuyitFixit Ok. You measured it at 0V so that was a bit weird. The chip must have been bad either way as the board started working once you replaced the chip! Just thought you might have paused for consideration when you measured 0V there!
Yep chip was bad, from memory I think the datasheet said it had an internal pullup connected to vref, so it should have measured a voltage even when not connected to anything which is why I knew it was the chip. Thanks for commenting 👍🙂
Plug a switching power supply into a dirty generator will blow something. THD needs to be 5% or less.
I told you at the start of the video "it's the controller", and now at 16:45 I may end up with egg by the end? :)
No happy about the cap imbalance! Nothing to do with no operation though I expect!
YEAH! No Egg!!!!!!!!!!!!
I have very good eyesight apparently, and you are missing a few words in your disclaimer ;)
😂😂😂 ...Uses smaller font on next one...
How can I send a device to you ? No matter the cost to me.
Drop me an email. It's the channel name at outlook dot com.
Mosfet/igbt/power switching Semiconductor heatshink not sufficient, design doesn't have thermal shutdown system
You should explain what you are doing better
Thanks for the feedback Steve. I'm not sure what levels people are at who are watching. What things would you like me to explain better?
@@BuyitFixit It's interesting feedback, some people will know how to break down and diagnose an iphone fault, others won't know which end of a hammer to hold! You seem to be doing something right!
smps are a joke. pocket size unreliable and expensive to get repaired. Add to that all those other components to make it work. So apart from the weight, what is the point?
Cost and size and efficiency. Copper is expensive. You would need a huge copper transformer at mains frequency to do the same job and waste a lot if heat. That's why they up the frequency.
@@BuyitFixit Not very efficient if they keep busting are they! So are you saying all those extra add ons like transistors capacitors, resistors they make come free do they? Great if that's the case... free energy :)
No, not free, just cheaper than a huge lump of copper. And as you say, a lot more complex and probably more unreliable than an old linear power supply.
@@BuyitFixit Indeed. So glad we examined and came to a critical and logical conclusion with sensible civil discussion. Thank you.
Sorry to be a pooh pooh, but leaving your solder wire so close to the work area is inviting being ZAPPED!!!!!!!!!!!!!!!
No problem, nothing wrong with that advice at all 👍
dont you ever use a scope in xy mode+a iv curve tracker(ie huntron tracker type thing),very handy things,spot faults at a glance.
Thanks, I've not heard of these before. I think the only time I've really used a scoop in XY was years back when adjusting laser disc players 😂I'll have a look into what you suggested 👍