Here's a pro tip I've been taught 50 years ago from a TV repair tech: If you have an open resistor you want to know its original value, just scrape a sharp knife over the length of the bad resistor, then measure from the center of the scraped free resistor body to both legs of the resistor. One side will read open, the other will read roughly the half of the original value.
Given the position and job, it's probably toasted in the other ones, so reading the bands would be tricky at best. Measuring in circuit tho, that'd work.
Aishi caps; not nichi or ruby, but still far higher quality than I would have expected in such a unit. Also, please NEVER stop posting the videos where things go sideways!!! These are so important for lots of us to learn that mistakes happen, its not the end of the world, we learn something from it, and we move on. It also gives us a glimpse into the thought process leading up to the smoke, and the thought process AFTER the smoke. SUPER important!!
One little trick for dealing with burnt resistors is to clip a probe to a knife, and to use the knife as a probe that can cut through the layer of laquer on the resistor right in the middle. With a bit of luck, you can still measure one half of the resistor, and then find an approximate value of it by doubling the measured value. If one half is open circuit(ish), try the other.
i like this idea better. thank you for bringing it up as it would not have occured to me otherwise. it seems worth it for the extra 1 step to try and costs nothing at all, with no risks. worst case you cannot always get the resistance value, then need to turn back to other methods. nothing lost
As I repair something connected directly to main power supply, I connect the device in series with an old good light bulb. The light bulb should be the same power as a device. In this case I would use 25W light bulb. If your device has short circuit or from some other reason consumes more then expected - you've simple got lighting bulb and no damage
More videos like this please!! It’s so reassuring to us amateur electronics engineers to know that the pros can make smoke as well as we do. Brought a smile to my face on a grey and rainy day in the north east of England.
I tried the same reair on a similar power source (electronic ballast i was using for a HV power supply) and it smoked the same way. I think there is another problem and that resistor is the first one to go. Once you replace it, something else gives off the magic smoke. Those damn things are un-repairable chinesium.
Agreed I'm thinking sure these things are not designed to actually power LED's to their full potential advertised lifespan, but that resistor also should not have crapped out without a separate failure.
I'm guessing the resistor is probably around 100k minimum and it was a 15.6v zener; 15.6V zeners are very common on these types of supply because it allows operation of 12V nominal supplies with some headroom for shitty regulation. I'm guessing 100k because at completely un-dimmed level you want less than 1W dissipation, so 240V RMS - 15.6V is 224.4V, 224.4V is 50.355k ohm ((v*v)/p = r) but you gotta assume 100% duty cycle with a reasonable lifetime so you're not gonna run 50k, you're gonna run higher, probably 100k-200k. Looking at the resistor, the color bands were probably red-brown-yellow-brown for 210k
The root cause seems to be the loss of capacitance of the cap near the switcher IC. The resistor is toasted during continuous charging of this cap. Normally the IC will be powered by the Aux Winding after startup. Great fireworks👍
but this resistor is never disconnected from the high voltage, it will not heat up appreciably more if the cap is dead, and a bit if current is diverted off the zener into the pwm chip... I still don't get it.
@@victortitov1740 hmm maybe if the cap is shorted rather than a loss of capacitance? Then the resistor leg is 0.4-0.6V above around instead of the zener voltage. Or maybe the zener itself was shorted to begin with? hard to say.
@@eDoc2020 hmmm actually it depends on it's initial value, if it was 22k originally there would be ~37V over that and the zener because of the 180k. But you are right that's not enough to pop it, must have had close to the full rectified voltage across it somehow?
Dave you could have soldered in a variable resistor. and started high at then slowly reduced the value. until the circuit started booting and working again. then after finding the value replace the pot with a decent fixed value higher wattage resistor
@@felixcosty Most I've come across may have it in the datasheet / label, but they generally are meant for signals only. If you need ones that will survive, have a look for a rheostat that is pretty much the old fashioned equivalent of a dimmer or speed controller.
Come on, Dave -- slap an 18V Zener and a 20k resistor in that thing and give it another try! And yes, a full reverse engineering video would be most welcome.
The switching IC is probably toasted after his experiment. The switching IC is toasted, because the zener is toasted. He could measure the zener, if it's a short, there's a small chance the switching IC survived.
So how to discover the resistor value, when it is fried: take a knife and scrape the top layer of it. Open the resistive material inside. Grab the multimeter and measure resistance between the leg and 1/2 of the resistor. Multiply by 2. Done!
I think there is an error in your reverse-engineered schematic. That diode going off to the transformer is not connected to the primary coil, that would not make sense. Instead it is connected to another winding that has the other side connected to ground. The 180k is the startup resistor, after the switcher has started the voltage from the extra winding feeds the IC via that diode, the resistor you changed, and the zener to ground.
I remember replacing a bad 10W ceramic resistor in an old TV long ago. There must have been some other fault that shorted the resistor across mains because the new resistor exploded into ceramic fragments. Now that was one big and loud explosion! Usually resistors aren't designed to heat up that much, so a failed resistor likely means there's some other problem.
Luv it! had a guy do a very similar thing at work after I said I would take the time to look into it, but he knew better and dropped a resistor in that he thought was right by just using the MK1 eyeball and poof let there be light and smoke ... A trap for old players (sorry couldn't help it lol). I wonder if it stings more knowing you had other lights in the house that you could have just took apart in situ and took a quick pic of the area you needed and then brought that back to the bench, no reverse engineering needed really if that was the case. Oh well least the smoke alarms didn't go off.
The thing I find with chopper and SMPS a is that once you fry something usually everything goes… That transistor zener circuit provides the DC supply to controller chip … I think the feedback diode is used as a flywheel and would be used to keep the chopper circuit running in the event of a brownout situation where the mains dips for a moment. Been a few years since I worked with Tamtec on their light engines and associated designs
EEEWblog: Electrical Engineering E-waste blog :) I really like that you post this, it really shows that even the most talented and experience people sill needs to have their brains engaged, and that sometimes we all do silly mistakes like that.
I think if the Zener diode fails to open everything else would be destroyed including the IC since you would have the high voltage going thru the Vbe of the BJT direct to the IC :), what is interesting is that they are using this method as a snubber.
I'd love to see you reverse engineer/fix this. I learn most of the videos where you follow through, particularly because as an electronics novice I often make things worse before I fix them... 😁
I am seeing a lot of led bulb drivers being mains reference now, basically a APFC circuit driving the leds, just to improve PF and they still get quite hot.
Good-on-ya Dave ! Can't believe you did that (lol). I thought the rule was, 'start big then work down'. A quick bit of math, and it was 210 ohm if the Zena was 5.1. My money is on the bjt going tits-up..
Well that's what I thought the colors might indicate as well. But wouldn't that be a lot more than 1W? Was trying to guesstimate the voltage expected across it, and it certainly looks like it was running hot, so R = ^2/ 1W ?? At 210 ohms, might have had 14-15 volts across it?
@@mikefochtman7164 Thats a good point, and 210 is not a common value. It is safe to assume the Tolerance band is gold. That said, we still have the question, 'what failed first ?'. The extensive "browning" of the resistor would suggest that it failed over time, be it seconds or weeks. Think I'll rewatch the vid. ;)
That resistor should be in hundred k ohm range, not ten's k range. The voltage drop on it is hundred volt level. So the resistance of it may not be changed.
My logic would have been to check the PSU from the working light to get the correct value (Assuming the PSU is identical between the 2 lights seen in the other vid..) But I'm not good at electronics. :-P I wouldn't know how to diagnose like Dave. ^_^
Usually when I have a power source that does that, it gets replaced as a whole. Replacing one part of the unit that's been over heated and damaged is not worth it.
You've just got to try it sometimes, this shows the reality of repairing someone else's crap, excellent video Dave it's a shame we can't thumbs up more than 1. Thanks for showing it warts and all.
Ahhh, why didn't you measure the voltage across that resistor before adding it? You could guess the power absorbed in it based on the voltage measurement.
On burnt high wattage open circuit resistors, I find you can get an idea of value by chipping the paint off and measuring each side of the resistor windings to the break, gives very good results.
I haven't finished the video yet, but when you measured the resistor at about 11:40 you were still in diode mode on the software in the top right... :)
Murphy's law of electronics and electrical engineering: Wherever a fuse is protecting a circuit, the circuit will blow, keeping the fuse intact. Sometimes pyrotechnic effects are included :)
A startup resistor in a switching power supply does have a high value. Its function is to power up the switching IC directly from mains until the the switching transformer takes over. It's in series with the switching IC power supply. I think it's red purple orange, and I think that despite its looks, it's not broken. You can calculate the minimum resistor value by reading the zener voltage. You know the power supply, 230*root(2). You know the wattage of the zener, so you know the maximum current. And then it's just use ohms law to calculate the minimum value. The zener voltage must be below 50V, because the cap is only 50V. I think the cap was gone-ski :) And this is the reason for the initial problem.
Absolutely love it! So glad to see it happens to you and not just me like that. You are far more adventurous than me. I have never guessed at a value before.
This is a really bad design. The resistor should be lifted away from the board to help heat dissipation. The capacitors are not only under the heat sink but also right next to the resistor. A timing device for planned obsolescence.. The resistor is part of the startup circuitry probably 47K or 100K
So many LED circuits are designed to fail quickly, either by cooking the driver or burning the LEDs. Light bulb companies don't want to let go of that nice income flow they've had since incandescents were top of the line. Look up Big Clive's video on the Dubai lamps that can't be bought outside one small gulf nation for how they SHOULD be built.
I think it is important to always show testing and discharging the high voltage caps. When I was starting out I actually watched a bunch of videos on how to fix a TV power board and non of them mentioned it. Lucky for me I shorted the caps with a screwdriver because there were several caps still charged and even the next morning they had quite a bit of charge left. I could still get sparks from random caps 2 days after disconnecting power and letting the discharge LED go dark.
You knew that infinitely big value (open) allows protection to kick before something awful happens, so even without RE a safe play would be to start with a big value and lower it in some steps. Still a fun video.
Yes good idea, however you have to be careful as I believe these substitution have low power/current ratings. Not sure what that rating was but appeared say 1W or more.
You mentioned the module uses secondary regulation, but there's an optoisolator from the secondary side to the primary, which would indicate the regulation is done on the primary side.
This reminds me. Way back i saw an investigation in maintenance/repair actions. I forgot the exact number but in something like 30% (yes this high) of the cases that something needed to be repaired the technician made a mistake and by doing so caused an extra problem that needed to be fixed. The mistake could be something like slipping with a screwdriver/drill (and damaging something), put to much voltage on an input, made the wrong adjustment, connected the wrong wires, using the wrong tool, used the wrong procedure and so on. That's why i hate to bring my car to a garage..
If the resistor value is 10K then at startup its DC conditions will approx 32mA which is about 10W. Not sure what the running conditions would be but I'm thinking that 30K + might be nearer the mark for long term running. The pigments in the colour bands can be anything after severe heating.
some manufacturers have this really nasty habit of scraping SMD codes off components of their designs. It's infuriating and screams 1-planned obsolescence and 2-exclusive servicing.
They need a massive amount of capacitance on the input but the whole circuit functions a bit like an APFC unit and the capacitance has been kept low to improve the power factor and therefore the 0.9 PF.
They control output voltage. Once it gets above some value voltage on one of the pins of the controller IC gets above some threshold as well and the controller starts to skip its pulses. It has nothing to do with the circuit that powers the controller IC itself.
I worked as a design engineer for Tamlite and they used a simple hold off circuit which disabled the Chopper circuit until the input rectified DC across the smoothing cap had reached something in the order of 90v DC to prevent the controller IC from chattering … that utilised a small NPN transistor and zener arrangement …. Just wondering if it’s something similar? Guess I should watch to the end before commenting hahah😀😀😀
Joey Here. I'm Saying There's a shorted component on that board. I'd say after watching your entire vid. One of the diodes was shorted to cause the resistor to get hot. There's has to be.
I did something similar repairing a control board in a 30 year old built in microwave/electric oven combo. Replaced a burnt resistor with what I thought was the correct value. Turns out the "resistor" was actually a small value picofarad cap in the exact same package as your bog standard axial resistor. The "C4" silkscreening on the PCB should have tipped me off, but I assumed it was a typo and/or convinced myself it was the label for the neighboring component as I had never before seen a capacitor in that type of package
@@St0RM33 Except they don't need to. If the engineers who design them would allow for a few extra cents/pence/pesos/rubles in the BOM, they could last a f**king long time, but then the municipality wouldn't be buying replacements any time soon. There's a tradeoff between cost and longevity, and the needs of the business favor designs that will work just long enough to not adversely impact future demand. I suppose it's good in terms of maintaining the need for municipal workers to do the replacement work; we still need people like Big Clive to be able to afford their random Poundland teardown fodder.
@@petersage5157 i agree with you; planned obsolescence, i'm an engineer myself but i don't like to work this way..for me devices should work forever and never fail in all conditions. I get pissed off by nowadays shitty products that i might spend up to 10x the cost just to make my own. The problem with led lights is functional too; sodium lamps produce a monochromatic light that works much better for night driving; yes the overall luminous flux is lower but the tend to light a lot more uniformly than the focused light of leds which is a lot more distracting and affects wildlife negatively as well; technology connections YT channel made a video with a much deeper analysis on this subject
@@St0RM33 Alec did a great job on that video; I think it was some of his best work. Clive (and I think Alec?) has/(had) pointed out that the optics on LED replacement street lamps can protect wildlife and our dark skies while confining the illumination to the road surfaces where it's needed. As for the color temperature/spread, that's a choice that the designers and buyers have to make. Street lights are available in the 2700K candlelight range, which is safe for migratory wildlife that rely on the 6000K moon as a guide, but many municipalities balk at the extra 1-2% watt per lumen. One of my Bucket List projects is a small, affordable, heirloom-quality solid state analog guitar amp that can be used for everything from pub gigs to "don't wake the baby" practice. I keep coming a-gutsa on the need for coupling and reservoir caps in the tens and hundreds of microfarads. I could build something like this with parallel clusters of polyputthekettleon for myself and my nieces, but I can't design for manufacture without electrolytics, which would eventually need replacing.
Have replaces 100's of these, went with a big brand dim-able and dim-able globes but there were no dimmers and the amount of daily replacements went form several to rarely and most of the problems were from these units that lasted longer than the rest.
I have a suspicion that the main MOSFET turned on. I don't know as you'd get enough current though the small diodes to set fire to the input resistors. But if that big MOSFET turned on, major magic smoke. Perhaps the Zener failed open, pumping high voltage into the driver.
Dave... they make these to fail on purpose. LEDs usually have a MTBF of like 27 years. This is bad for profit, so the drivers are run super hot and die prematurely. I just disassembled two light-bulb-styled LEDs from GE and the LED modules are fine. FR4 boards are black, crispy, and shattered when I touched them. x-x
That circuit looks like voltage limiting one. Zener, resistor and transistor. Value might be in 10k or higher to limit the flowing current. Nice fireworks 😅
Next time add a series 40W to 100W incandescent light bulb to mains input. So when there is an issue with the repair you made, the lamp would light up, and the video would be much longer😎👍
I believe I saw 200 ohms. Also, the resister did not go bad on its own. I would suspect the capacitor. Just because a cap is not puffed up, does not mean it is still good. oh, zener, good chance it is the cause. what ever it is, caused the resister to flow more current and overheat. The ristor increased in value which saved the rest of the unit.
YES!!!!!!! A complete redesign and reverse engineering with schematics and user manual..... on my desk in the morning young man - and no TV until its done and tested !!!!!!
Here's a pro tip I've been taught 50 years ago from a TV repair tech: If you have an open resistor you want to know its original value, just scrape a sharp knife over the length of the bad resistor, then measure from the center of the scraped free resistor body to both legs of the resistor. One side will read open, the other will read roughly the half of the original value.
Wow thanks for the tip
Great tip, thanks!
Nice tip indeed! Thanks for your comment!
Brilliant
Not a bad idea but it won't always work because the heat could have affected the resistive material over more of the length than the open portion.
I learned something: When in doubt about the multiplier band, start with the largest resistance it might be, and work your way down.
We started with open resistor 😂😂
It would definitely have been a good idea
Depends on the circuit though, in some cases a higher value could be riskier. Better to draw out the schematic and get more information.
smokin!!!
Or open another oyster that hadn't fried
@@Agent24Electronics how could it be riskier?
Open one of the other lights you have in your ceiling and check the value of the resistor
Right?!
Hey, we all make boneheaded moves from time to time. If only more were willing to share the oopsies too we'd all be better off.
@@matthewellisor5835 I give Dave credit for posting the video
I'm betting Dave didn't want to drive home to get it. Lesson learned...try to have a working item for comparison.
I know….. I was also screaming this at the screen too!! :)
Given the position and job, it's probably toasted in the other ones, so reading the bands would be tricky at best. Measuring in circuit tho, that'd work.
Aishi caps; not nichi or ruby, but still far higher quality than I would have expected in such a unit.
Also, please NEVER stop posting the videos where things go sideways!!! These are so important for lots of us to learn that mistakes happen, its not the end of the world, we learn something from it, and we move on. It also gives us a glimpse into the thought process leading up to the smoke, and the thought process AFTER the smoke. SUPER important!!
Yeah, I use the aishi caps I often find in fluorescent lights
Once I also found a psu with two of them for filters.
My goof is your gain..... totally agree! (Everybody learns something)
High voltage caps from Aishi are ok. They are commonly seen in LED drivers.
One little trick for dealing with burnt resistors is to clip a probe to a knife, and to use the knife as a probe that can cut through the layer of laquer on the resistor right in the middle.
With a bit of luck, you can still measure one half of the resistor, and then find an approximate value of it by doubling the measured value. If one half is open circuit(ish), try the other.
i like this idea better. thank you for bringing it up as it would not have occured to me otherwise. it seems worth it for the extra 1 step to try and costs nothing at all, with no risks. worst case you cannot always get the resistance value, then need to turn back to other methods. nothing lost
Bingo.
nice trick! thanks!
or check datasheet for basic set :)) or ration calculation :)) is worthy is acurate no trick ..
As I repair something connected directly to main power supply, I connect the device in series with an old good light bulb. The light bulb should be the same power as a device. In this case I would use 25W light bulb. If your device has short circuit or from some other reason consumes more then expected - you've simple got lighting bulb and no damage
Yes, old mains repair trick.
Wow cool!
100 year old trick, still as good today as it was back then 😃
With SMPS Ive found the dim bulb trick not always works too good. It stops the Thing Under Test from burning, but rarely permits it to start
Would a variac have helped?
More videos like this please!! It’s so reassuring to us amateur electronics engineers to know that the pros can make smoke as well as we do. Brought a smile to my face on a grey and rainy day in the north east of England.
"pros"?
Ha!
I tried the same reair on a similar power source (electronic ballast i was using for a HV power supply) and it smoked the same way. I think there is another problem and that resistor is the first one to go. Once you replace it, something else gives off the magic smoke. Those damn things are un-repairable chinesium.
Love that you took the time to reverse engineer it to show us exactly what happened!
Agreed! Repair videos like these are fantastic.
Usually replacing a burnt resistor it's not a good idea unless you have the root cause
Yes, yes and thrice YES.
Agreed I'm thinking sure these things are not designed to actually power LED's to their full potential advertised lifespan, but that resistor also should not have crapped out without a separate failure.
I have learnt that the hard way
value of input resistor:
black-black-black-black
good thing you got all on video
I'm guessing the resistor is probably around 100k minimum and it was a 15.6v zener;
15.6V zeners are very common on these types of supply because it allows operation of 12V nominal supplies with some headroom for shitty regulation.
I'm guessing 100k because at completely un-dimmed level you want less than 1W dissipation, so 240V RMS - 15.6V is 224.4V, 224.4V is 50.355k ohm ((v*v)/p = r) but you gotta assume 100% duty cycle with a reasonable lifetime so you're not gonna run 50k, you're gonna run higher, probably 100k-200k.
Looking at the resistor, the color bands were probably red-brown-yellow-brown for 210k
Probably a bit more than a 15v Zener; many controller chips don't startup until 16 volts.
Agree was thinking 48k min
Many flyback control IC go to hiccup mode when they detect overcurrent/short-circuit condition, so fault can be easy on secondary side.
11:19 You are in the diode mode, Dave...
The root cause seems to be the loss of capacitance of the cap near the switcher IC. The resistor is toasted during continuous charging of this cap. Normally the IC will be powered by the Aux Winding after startup. Great fireworks👍
but this resistor is never disconnected from the high voltage, it will not heat up appreciably more if the cap is dead, and a bit if current is diverted off the zener into the pwm chip... I still don't get it.
@@victortitov1740 hmm maybe if the cap is shorted rather than a loss of capacitance? Then the resistor leg is 0.4-0.6V above around instead of the zener voltage. Or maybe the zener itself was shorted to begin with? hard to say.
@@funkyironman69 A shorted Zener wouldn't make it smoke; the Zener voltage is an order of magnitude less than the voltage across the resistor.
@@eDoc2020 Yeah good point, maybe the 180k went short then?
@@eDoc2020 hmmm actually it depends on it's initial value, if it was 22k originally there would be ~37V over that and the zener because of the 180k. But you are right that's not enough to pop it, must have had close to the full rectified voltage across it somehow?
Dave you could have soldered in a variable resistor. and started high at then slowly reduced the value. until the circuit started booting and working again. then after finding the value replace the pot with a decent fixed value higher wattage resistor
Just wondering would a decade resister work instead of a variable resistor.
@@felixcosty As long as your decade box has 1W resistors. Most don't.
Most are not 1W and high voltage rated
@@EEVblog How can you tell what the variable resisters wattage is?
@@felixcosty Most I've come across may have it in the datasheet / label, but they generally are meant for signals only. If you need ones that will survive, have a look for a rheostat that is pretty much the old fashioned equivalent of a dimmer or speed controller.
Come on, Dave -- slap an 18V Zener and a 20k resistor in that thing and give it another try! And yes, a full reverse engineering video would be most welcome.
Yes, lets see this baby repaired.
The switching IC is probably toasted after his experiment. The switching IC is toasted, because the zener is toasted. He could measure the zener, if it's a short, there's a small chance the switching IC survived.
"i guess its the wromg value!"
...his famous last words
flashing translates to 4, 8, 15, 16, 23 and 42 and must be entered every 108 minutes.
At least until Jack shows up and everything goes sideways.
Oh, wow, unlisted video. I'm in the Matrix.
7:01 That's an S, not a 5. There could have been some worries had that been a higher-voltage 2SC device than the 945.
Yes, noticed this on the edit but forgot to add the overlay.
Saw this too, as soon as I saw '945 on the second line I knew exactly which jellybean it was!
Looking forward to Part 2 of repairing this unit :P
So how to discover the resistor value, when it is fried: take a knife and scrape the top layer of it. Open the resistive material inside. Grab the multimeter and measure resistance between the leg and 1/2 of the resistor. Multiply by 2. Done!
sometimes the coil has degraded and oxidized when exposed to such extreme heat.
@@martininm.t.r.a9887 yep, but not always! you still have a chance
I haven't tried this myself by I've read about it before.
Wow, everything I asked for in the eevblog survey in a single video!! As always a great educational video
Dave rarely fails to fix something, it's kind of refreshing 🤣
I think there is an error in your reverse-engineered schematic.
That diode going off to the transformer is not connected to the primary coil, that would not make sense.
Instead it is connected to another winding that has the other side connected to ground.
The 180k is the startup resistor, after the switcher has started the voltage from the extra winding feeds the IC via that diode, the resistor you changed, and the zener to ground.
It says "we've been trying to contact you about your cars extended warranty".
LoL
I remember replacing a bad 10W ceramic resistor in an old TV long ago. There must have been some other fault that shorted the resistor across mains because the new resistor exploded into ceramic fragments. Now that was one big and loud explosion! Usually resistors aren't designed to heat up that much, so a failed resistor likely means there's some other problem.
Luv it! had a guy do a very similar thing at work after I said I would take the time to look into it, but he knew better and dropped a resistor in that he thought was right by just using the MK1 eyeball and poof let there be light and smoke ... A trap for old players (sorry couldn't help it lol). I wonder if it stings more knowing you had other lights in the house that you could have just took apart in situ and took a quick pic of the area you needed and then brought that back to the bench, no reverse engineering needed really if that was the case. Oh well least the smoke alarms didn't go off.
The thing I find with chopper and SMPS a is that once you fry something usually everything goes…
That transistor zener circuit provides the DC supply to controller chip … I think the feedback diode is used as a flywheel and would be used to keep the chopper circuit running in the event of a brownout situation where the mains dips for a moment. Been a few years since I worked with Tamtec on their light engines and associated designs
EEEWblog: Electrical Engineering E-waste blog :)
I really like that you post this, it really shows that even the most talented and experience people sill needs to have their brains engaged, and that sometimes we all do silly mistakes like that.
You could have tried to scrape the soot/oxidisation layer on the resistor carefully to see the original colour bands.
I think if the Zener diode fails to open everything else would be destroyed including the IC since you would have the high voltage going thru the Vbe of the BJT direct to the IC :), what is interesting is that they are using this method as a snubber.
Zeners rarely fail open.. But the way they apparently recover energy is indeed very interesting. I'd be in favour of a full reverse engineering.
I'd love to see you reverse engineer/fix this. I learn most of the videos where you follow through, particularly because as an electronics novice I often make things worse before I fix them... 😁
YES !
I am seeing a lot of led bulb drivers being mains reference now, basically a APFC circuit driving the leds, just to improve PF and they still get quite hot.
Next time i hiccup, i will look for a burned resistors in my body!) Thanks!
Imagine a lamp that gives you bios codes like a computer when it fails...
Good-on-ya Dave ! Can't believe you did that (lol). I thought the rule was, 'start big then work down'. A quick bit of math, and it was 210 ohm if the Zena was 5.1. My money is on the bjt going tits-up..
Well that's what I thought the colors might indicate as well. But wouldn't that be a lot more than 1W? Was trying to guesstimate the voltage expected across it, and it certainly looks like it was running hot, so R = ^2/ 1W ?? At 210 ohms, might have had 14-15 volts across it?
@@mikefochtman7164 Thats a good point, and 210 is not a common value. It is safe to assume the Tolerance band is gold. That said, we still have the question, 'what failed first ?'. The extensive "browning" of the resistor would suggest that it failed over time, be it seconds or weeks. Think I'll rewatch the vid. ;)
"Start dissipating a few hundred watts, then work down" :D
This is the rule for a field technician. For TH-cam technicians it's the other way around.
That resistor should be in hundred k ohm range, not ten's k range. The voltage drop on it is hundred volt level. So the resistance of it may not be changed.
Lesson learnt: Always go for the highest possible value if you can't confirm a specific color
My logic would have been to check the PSU from the working light to get the correct value (Assuming the PSU is identical between the 2 lights seen in the other vid..)
But I'm not good at electronics. :-P I wouldn't know how to diagnose like Dave. ^_^
Just discovered you channel, just a beginner but your making me realise I might want to start messing around with electronics :)
Usually when I have a power source that does that, it gets replaced as a whole. Replacing one part of the unit that's been over heated and damaged is not worth it.
That's what you get for hoping my next project doesn't work! 🤣
You've just got to try it sometimes, this shows the reality of repairing someone else's crap, excellent video Dave it's a shame we can't thumbs up more than 1. Thanks for showing it warts and all.
This is great! Makes me feel better about all the stuff I blow up on the bench.
Ahhh, why didn't you measure the voltage across that resistor before adding it? You could guess the power absorbed in it based on the voltage measurement.
On burnt high wattage open circuit resistors, I find you can get an idea of value by chipping the paint off and measuring each side of the resistor windings to the break, gives very good results.
Definitely, a gained experience thankyou dave for showing and explaining the mistake
At least the smoke & flames didn't escape while the unit was installed in your ceiling!
I'd like to see a full reverse engineering video to learn more please but thanks again for another educational video Dave
I like that you post your errors. I learn from them as well.
I haven't finished the video yet, but when you measured the resistor at about 11:40 you were still in diode mode on the software in the top right... :)
I was so annoyed seeing that, and glad too as it is something I do myself a little too often =)
@@magnuslindgren9460 I have as well many times lol
Murphy's law of electronics and electrical engineering:
Wherever a fuse is protecting a circuit, the circuit will blow, keeping the fuse intact.
Sometimes pyrotechnic effects are included :)
"DaveCAD FAIL EDITION" - haha, you are the best!
What not to do is sometimes more informative than what TO do. Excellent video!
A startup resistor in a switching power supply does have a high value. Its function is to power up the switching IC directly from mains until the the switching transformer takes over. It's in series with the switching IC power supply. I think it's red purple orange, and I think that despite its looks, it's not broken.
You can calculate the minimum resistor value by reading the zener voltage. You know the power supply, 230*root(2). You know the wattage of the zener, so you know the maximum current. And then it's just use ohms law to calculate the minimum value. The zener voltage must be below 50V, because the cap is only 50V. I think the cap was gone-ski :) And this is the reason for the initial problem.
Repair videos are always interesting. Even when things end up on fire.
Absolutely love it! So glad to see it happens to you and not just me like that. You are far more adventurous than me. I have never guessed at a value before.
Hi Dave, please get yourself a Cliff Quicktest like BigClive uses. Those live un-insulated alligator clips should only be used by ElectroBoom.
Maybe Dave does it this way in honour of Steve Irwin ;-)
This is a really bad design.
The resistor should be lifted away from the board to help heat dissipation.
The capacitors are not only under the heat sink but also right next to the resistor.
A timing device for planned obsolescence..
The resistor is part of the startup circuitry probably 47K or 100K
So many LED circuits are designed to fail quickly, either by cooking the driver or burning the LEDs. Light bulb companies don't want to let go of that nice income flow they've had since incandescents were top of the line. Look up Big Clive's video on the Dubai lamps that can't be bought outside one small gulf nation for how they SHOULD be built.
@@truckerallikatuk The situation with the Dubai lamps is despicable.
I love the smell of frying resistors in the morning!
I think it is important to always show testing and discharging the high voltage caps.
When I was starting out I actually watched a bunch of videos on how to fix a TV power board and non of them mentioned it. Lucky for me I shorted the caps with a screwdriver because there were several caps still charged and even the next morning they had quite a bit of charge left. I could still get sparks from random caps 2 days after disconnecting power and letting the discharge LED go dark.
You knew that infinitely big value (open) allows protection to kick before something awful happens, so even without RE a safe play would be to start with a big value and lower it in some steps.
Still a fun video.
You could have also used a resistor substitution box and started it 100K and work down whilst the circuit is active and observing the behavior
Yes good idea, however you have to be careful as I believe these substitution have low power/current ratings. Not sure what that rating was but appeared say 1W or more.
You mentioned the module uses secondary regulation, but there's an optoisolator from the secondary side to the primary, which would indicate the regulation is done on the primary side.
Should've grabbed another power supply from the kitchen lamps to compare with. Oh well, magic smoke is fun on an affordable level. Lol
This reminds me. Way back i saw an investigation in maintenance/repair actions. I forgot the exact number but in something like 30% (yes this high) of the cases that something needed to be repaired the technician made a mistake and by doing so caused an extra problem that needed to be fixed. The mistake could be something like slipping with a screwdriver/drill (and damaging something), put to much voltage on an input, made the wrong adjustment, connected the wrong wires, using the wrong tool, used the wrong procedure and so on. That's why i hate to bring my car to a garage..
I think you measured the resistor in diode mode after removing it from the board !
If the resistor value is 10K then at startup its DC conditions will approx 32mA which is about 10W. Not sure what the running conditions would be but I'm thinking that 30K + might be nearer the mark for long term running. The pigments in the colour bands can be anything after severe heating.
More like "Godzilla Facepalm". For when epic is not enough.
some manufacturers have this really nasty habit of scraping SMD codes off components of their designs. It's infuriating and screams 1-planned obsolescence and 2-exclusive servicing.
They need a massive amount of capacitance on the input but the whole circuit functions a bit like an APFC unit and the capacitance has been kept low to improve the power factor and therefore the 0.9 PF.
They still control something on the primary side from secondary via that optocouple.
Feedback loop for regulation.
They control output voltage. Once it gets above some value voltage on one of the pins of the controller IC gets above some threshold as well and the controller starts to skip its pulses. It has nothing to do with the circuit that powers the controller IC itself.
Surely there is high-def video of you opening one of these in the past where you could get the resistor code from?
i love the mishaps tho, always learn heaps from you Dave!
In Morse, it reads: "Help, I'm trapped in a Chinese LED factory."
FULL BRIDGE RECTUMFRIER!!!!!111
6:35 The way he pauses as he's saying it, then says it normally. In case anyone is missing the context: th-cam.com/video/sI5Ftm1-jik/w-d-xo.html
Its great that you intentionally sacrifice working equipment to replicate a cock-up and thus educate use Dave. Your my hero ...
Video idea - get a bunch of resistors with different values and see what colour the bands go after being cooked up a bit...
Well, you managed to stop it from flashing ;-)
the morse code say.... "its F* up buy a new one. its chinese" hahahahaha
I worked as a design engineer for Tamlite and they used a simple hold off circuit which disabled the Chopper circuit until the input rectified DC across the smoothing cap had reached something in the order of 90v DC to prevent the controller IC from chattering … that utilised a small NPN transistor and zener arrangement …. Just wondering if it’s something similar?
Guess I should watch to the end before commenting hahah😀😀😀
Joey Here. I'm Saying There's a shorted component on that board. I'd say after watching your entire vid. One of the diodes was shorted to cause the resistor to get hot. There's has to be.
I did something similar repairing a control board in a 30 year old built in microwave/electric oven combo. Replaced a burnt resistor with what I thought was the correct value. Turns out the "resistor" was actually a small value picofarad cap in the exact same package as your bog standard axial resistor. The "C4" silkscreening on the PCB should have tipped me off, but I assumed it was a typo and/or convinced myself it was the label for the neighboring component as I had never before seen a capacitor in that type of package
No worries Dave ... "it" happens ... normally with an "Sh" in front but it happens lol
I've often seen such "hiccuping" in LED street lights. That's what happens when municipalities give contracts to the lowest bidder.
same problem here..fuck led street lights they suck ass
@@St0RM33 Except they don't need to. If the engineers who design them would allow for a few extra cents/pence/pesos/rubles in the BOM, they could last a f**king long time, but then the municipality wouldn't be buying replacements any time soon. There's a tradeoff between cost and longevity, and the needs of the business favor designs that will work just long enough to not adversely impact future demand. I suppose it's good in terms of maintaining the need for municipal workers to do the replacement work; we still need people like Big Clive to be able to afford their random Poundland teardown fodder.
@@petersage5157 i agree with you; planned obsolescence, i'm an engineer myself but i don't like to work this way..for me devices should work forever and never fail in all conditions. I get pissed off by nowadays shitty products that i might spend up to 10x the cost just to make my own. The problem with led lights is functional too; sodium lamps produce a monochromatic light that works much better for night driving; yes the overall luminous flux is lower but the tend to light a lot more uniformly than the focused light of leds which is a lot more distracting and affects wildlife negatively as well; technology connections YT channel made a video with a much deeper analysis on this subject
@@St0RM33 Alec did a great job on that video; I think it was some of his best work. Clive (and I think Alec?) has/(had) pointed out that the optics on LED replacement street lamps can protect wildlife and our dark skies while confining the illumination to the road surfaces where it's needed. As for the color temperature/spread, that's a choice that the designers and buyers have to make. Street lights are available in the 2700K candlelight range, which is safe for migratory wildlife that rely on the 6000K
moon as a guide, but many municipalities balk at the extra 1-2% watt per lumen.
One of my Bucket List projects is a small, affordable, heirloom-quality solid state analog guitar amp that can be used for everything from pub gigs to "don't wake the baby" practice. I keep coming a-gutsa on the need for coupling and reservoir caps in the tens and hundreds of microfarads. I could build something like this with parallel clusters of polyputthekettleon for myself and my nieces, but I can't design for manufacture without electrolytics, which would eventually need replacing.
Youwe lucky, the zenner shorted and not poped open, else the primary regulator circuitry popup thru the transistor base 😂
Have replaces 100's of these, went with a big brand dim-able and dim-able globes but there were no dimmers and the amount of daily replacements went form several to rarely and most of the problems were from these units that lasted longer than the rest.
I have a suspicion that the main MOSFET turned on. I don't know as you'd get enough current though the small diodes to set fire to the input resistors. But if that big MOSFET turned on, major magic smoke. Perhaps the Zener failed open, pumping high voltage into the driver.
Dave... they make these to fail on purpose. LEDs usually have a MTBF of like 27 years. This is bad for profit, so the drivers are run super hot and die prematurely. I just disassembled two light-bulb-styled LEDs from GE and the LED modules are fine. FR4 boards are black, crispy, and shattered when I touched them. x-x
That circuit looks like voltage limiting one. Zener, resistor and transistor. Value might be in 10k or higher to limit the flowing current. Nice fireworks 😅
Next time add a series 40W to 100W incandescent light bulb to mains input. So when there is an issue with the repair you made, the lamp would light up, and the video would be much longer😎👍
That secondary probably produced around 20V p-p and the zener needs 1mA so the resistor was probably around 10k.
repair it! get it fixed! make it work!
Resistors seldom get hot to the point of destruction without a secondary reason.
10:50 200 ohm, 1W jobbie by the looks. (red, black, brown) With that, you can see the brown band is darker than the burnt portion.
I believe I saw 200 ohms. Also, the resister did not go bad on its own. I would suspect the capacitor. Just because a cap is not puffed up, does not mean it is still good. oh, zener, good chance it is the cause. what ever it is, caused the resister to flow more current and overheat. The ristor increased in value which saved the rest of the unit.
Look out ! the aliens called their mothership to tell them you are perfect for their experiments.... They will come soon...
YES!!!!!!! A complete redesign and reverse engineering with schematics and user manual..... on my desk in the morning young man - and no TV until its done and tested !!!!!!
I feel your pain. Just spent 2 hours trying to figure out how a + - 30vdc supply could be putting out + - 55vdc. Bad battery in my meter.