Fixing a dead digital thermostat
ฝัง
- เผยแพร่เมื่อ 26 ก.ค. 2024
- Checking out a faulty thermostat sent by Roger for our exploration.
For simple power faults like this one has it does actually make sense to do repairs.
With very predictable failure modes these days you don't need much electronics knowledge or experience to attempt a repair. A really common failure mode of compact switch mode power supplies is the capacitor on the low voltage side. That's because the very high frequency it operates at results in an amplified electrical stress. When the capacitor starts to fail its impedance increases and that causes an avalanche effect with the gassing of the electrolyte causing a buildup of pressure that domes the top of the capacitor and forces the electrolyte out through either the rubber seal at the base or the domed end (which is designed to rupture) as vapour.
The main thing to note is that you must use a low ESR (Low Equivalent Series Resistance) capacitor to deal with the high frequency operation, it should be the same capacitance value and a voltage equal to or greater than the original, and you must ensure it gets put in with the correct polarity.
A full replacement thermostat would have cost around £55 while the replacement capacitor was available as a pack of five for £1.
If you enjoy these videos you can help support the channel with a dollar for coffee, cookies and random gadgets for disassembly at:-
www.bigclive.com/coffee.htm
This also keeps the channel independent of TH-cam's advertising algorithms allowing it to be a bit more dangerous and naughty.
#ElectronicsCreators - วิทยาศาสตร์และเทคโนโลยี
In my experience, if you reverse the polarity on such a capacitor, it will disassemble itself, thus saving time. 😆
Tantalum caps do it in more spectacular fashion though
Aahhh The electroboom way….lol
Causes one hellova stink, to boot.
Some years ago, I repaired audio equipment. I opened up a mixing board that had a problem with its power supply. After repairing the power supply and over 100 electrolytic capacitors, it worked fine again. What a mess when I opened it up. I wish I had been there when it popped.
😂😂😂
Clive's "finger-test for confirmation" is something that always causes my heart to skip a beat. I'll never get used to that!
I feel, better get zapped when you expect it than later when not expecting it? Holding the iron or something.
i think we need to see an out-takes roll complete with expletives when that finger test has gone wrong!
Watching the repair and hearing you mention about getting "caught out" by failing to unplug it just reminds me of working on a power supply, and completely forgetting to do just that. Basically ended up inadvertently hot-swapping components on the live side while it was powered up the whole time. Fortunately it was on an isolation transformer, so no bangs, but still the entire time I'm wondering why the solder feels ever so slightly tingly when I touch it to each component to flow solder on after I put the component in, only to flip the supply over and see the power LED still lit. Neat.
That's impressive. I did the same but it end up shorting the main capacitor, nuking the rectifier, blowing the fuse and tripping apartment outlets section C16A breaker and main C40A breaker. Never again._
Worked on an electronics design like that. Because the soldering iron was grounded, it was a neat way to check the overcurrent protection was working. :)
It's a lot like firearms 101 - ALWAYS make sure it's not loaded (even when you 'know' it isn't) - ALWAYS make sure it's not connected (especially when you 'KNOW' it ain't)! Just stayin' safe.
The worst is when you have a bunch of things on the bench. You unplug what you are working on and then "BANG!" and then you realized you unplugged some test equipment instead.
Honestly, my trick with removing capacitors is to press on the same side of the cylinder as the pin I'm desoldering, until it budges a little. Then I switch to the other side, doing the same. It lets me rock it back-and-forth, making continual progress. The initial little movement feels minuscule, but makes all the difference.
Works a treat, since a lot of the time, like you experienced, I can't get purchase on the cap to do it the "lift" way. (Also because I'm not as dexterous and coordinated as you are with your fingers doubling as a helping-hand haha)
The only problem is when they've pinned it where the one ends up being smack up against a fixed object, either a heatsink or a transformer. Usually in either case there's still enough to rock it -- I mean lets at least *hope* the designers left enough room , otherwise I feel that'd be the textbook definition of how NOT to clearance such components -- but it takes longer to get it out since you only make the same limited progress each back-and-forth.
_(I am sure this is something we ALL have come to learn all on our own, but I'm hoping my sharing this will perhaps let someone spare themselves the time learning that! heh)_
---------
BONUS STORY: I remember when my computer PSU finally died on me. _(was a 430W Corsair, unpainted, just a model number, as it was before they cared about such things;)_
I had used that thing for probably a decade, buying it for when I built my Dual AthlonMP system (I had modded AthlonXP's by bridging the magical trace on the CPU lol), which then powered my two Athlon64 systems -- a Single Core, then a Dual Core, both Socket939.
Anyways, after we moved in 2009, I fire my system up and... nothin. Sadly, it took out that motherboard, and another one... And my CPU :(
So me being me, I tore the PSU apart to try and fix it, figuring it was the caps, and yea, lots were bad.
UNfortunately... I knew ZERO about that stuff, and so as I replaced them with salvaged caps from other stuff... I had NO idea I had soldered them back into the PSU....... with their polarity reversed... *:}*
On the plus side, I had enough sense about me to
A) take it outside before powering it up,
B) not have the PSU connected to anything, and
C) have its required pins shorted to turn it on (outside of a PC) BEFORE I plugged its power cable in, so I could be far enough back lol
Because yep, a split second after I plugged it in... *BANG.... BANG-BANG*
3 of the 6 caps I replaced, I had unknowingly soldered in backwards. That day I learned that some capacitors very much care which side is Ground and which side is Positive! (these were all on the DC Output side)
On the down side, I was done monkeying with that PSU trying to fix it.
On the up side, I found out a cheap way to make a nice bang noise! _(Some day I'll have to try it with a much much larger cap lol)_
Oooh, I’m currently wiring our house up with TEN of these things (ten zones). The Heatmiser back end is *beautiful* and a real treat for us DIY automation geeks. Highly recommend to UK automation enthusiasts. Eons better than Nest and all the other cloud heavy crap. I’d rather replace a faulty cap than get drawn in to some paid pricing plan later… It can be used in the cloud using their services but also completely independent of this and on your own local network. So if they ever go the way of some other providers, you can continue to use it from your own automation hub with zero dependence on them. They publish (not publicly - but available on request) their developer API and honestly it is so well thought through from a software point of view. Glad you made this, I suspect I may be watching this again in about 6 years ;)
How do these things work then, you have a thermostat in each room controlling individual radiators?
@@uK8cvPAq There shouldn't be any difficulty hooking up an individual control valve for each room, as long as the piping is set up to deliver hot water to each room individually. (From what I can see, I THINK that's the normal way to do it. I live in an apartment in a building that's old enough that the hot water heating is a retrofit, and I think that's how the piping is set up here.) It might get a bit tedious.
I used to own a home with electric heat in each room with an individual thermostat, and a device like this would be pretty much a drop-in replacement in such a system. (There was also a propane heating stove in the main basement room, which was a good thing considering that the climate here is slightly colder than it is in Moscow.)
Interesting as always. I use a bit of heat shrink tubing to remove awkward components.
I have an assortment of surgical implements of different sizes- hemostats and Kelly clamps- to use as handles. Heat shrink is a good idea if you're absolutely sure nothing nearby will object to the excess heat, and while Kelly clamps are pretty much guaranteed to bork a component like an electrolytic, well, it's already dead, isn't it?
Silicone tubing is my go to for gripping small cylindrical components like LEDs or electrolytic capacitors.
Excellent trick with the tape to help grip the component!
Thanks Clive for this - I had two similar Heatmisers ready for the bin, and while no capacitors looked to have visually failed, I replaced the 220µF capacitors and this has got both up and running :-)
I love the Newtonian desoldering at 8:15. I've practised this technique for almost 50 years. 😊
And there was me thinking “just get a solder sucker and a pair of helping hands”. Silly me, we can just use physics ;)
@@MatSmithLondon Downside to solder suckers on today's ultra thin PCB traces is they like to suck pads up too.
@Sideshow Bob's Fan Club agree, although I use braid sometime it does seem useless and generally burn myself regularly with it getting too hot just when I need it to actually work…
Newtonian method sounds good. I call it the Cillit Bang method of desoldering (bang and the solder is gone, along with all the ceramic caps 😅)
I would be worried about breaking something.
You are a legend among us mortal men, Sir Clive. I like these well explained diagnostics, repairs, and teardowns of faulty components in commercially available residential electronics vs. simple LED lights. Very informative. And I learned the toothpick or tap-on-bench method to clear the through holes approach. Clever.
May your juicy bits remain moist lol 😂
Great class, thank you. I've fixed 3 monitors and a television by replacing bad caps. They were all domed as you described.
A good fix indeed! Putting it back together sounded like a lot of components snapping off, but it worked! :D
That was the horrible friction fit case clips.
As long as the bits that break off stay inside the case, no problemo!! :-D
_„So let's recap quickly…“_ seems to be the motto of these years.
Its the price we pay for miniaturisation
Since around 20 years now, especially in computers. Around year 2000 began capacitor disease (lots of conspiracy theories about it) and also more widespread use of switching power supplies in various electronic. Usually these are cheapo caps dying rather quickly in such use.
They tried to make me go to recap, but I said "no, no, no"
@@Kwaq84 Was about to comment about the capacitor plague ; and yeah, it seems like we're getting the end of the bathtub curve these days, which was to be expected once we realized the plague was a thing.
As simple as they are, I remain impressed with the capability of capacitors.
If you consider that a rechargeable battery has a service life of a few thousand cycles, a capacitor on the other hand,
can cycle at 50+ Hz, 4,000,000+ times a day, every day, for years.
In fact this capacitor was part of a switch mode power supply running at a frequency several orders of magnitude higher than mains. If I’d have to guess up to around a Mhz. Ballpark 100,000,000,000 cycles/day. Fortunately, electrons don’t tend to get tired 😁
@@mlenstra _"Fortunately, electrons don’t tend to get tired"_ Tell that to some of the hardcore audiophiles (audiofools). I have genuinely seen someone recommend passing a DC current through their hyper-expensive speaker cables after some period of running to flush the old electrons out 😂
@@ferrumignis you gave me a brilliant idea! Let’s sell audiophile batteries pre-charged with special high fidelity audio grade electrons. AA size will be (limited time offer) just $999, enough to flush and fill up to six meters of speaker cable!
@@mlenstra I'm certain there are people that would buy this and swear they could hear the difference. After all these people were colouring in the edges of CDs with "special" expensive magic markers and swearing it improved sound quality, the same people will pay many hundreds of $ for an amplifier power cable made of silver wire, ignoring the many thousands of meters of copper and aluminium wire connecting their power socket back to the power station. Barking mad, but if you have no qualms about parting fools and their money then you could earn a good living.
@@mlenstra The worst bit is you will sell thousands of them.
Great work Clive. I liked that you pulled the cap apart as well. Well done.
I've seen DiodeGoneWild putting makeshift compound capacitors in the shells of dead Soviet-made capacitors. But they were huge, and he wanted to keep it as vintage-looking as possible, I guess.
My favourite part of Clive's videos is when he asks "Shall we open it up? - Yes"!!
I'm not sure I've ever taken apart an electrolytic (or seen one taken apart) - that roll was shorter than I expected. Nice to see a concrete symptom traced to the cap as well!
I took one apart once. I did it in a very expedient manner by hooking it up backwards. It contained both smoke and sound.
@@Know-Way tantalum caps were always my favourite, they also contain a fireball...
@@Know-Way so it went electro BOOM!
@@georgeprout42 It's been years since I blew up a tantalum cap by hooking it up backwards but I remember the smoke had a purplish or bluish color to it.
@@brianleeper5737 Yup. One of my team got the nickname Jimi Hendrix because of the fairly frequent purple haze coming from his bench.
Nice simple and straightforward...
I wonder if Rogers wants it back then...
Cheers,
He got it back.
@@bigclivedotcom Unfortunate that someone asked the question that no doubt many of us were wondering, but decided not to. Hopefully your post bag won't suddenly fill with dead electronics that people hope you will repair for them for free...
I was expecting fireworks at the beginning when you plugged it into mains - here in North America most HVAC thermostats run off a 24V AC supply generated by the furnace or air-handler.
I have a new Nest thermostat that didn't take kindly to overvolting, and their customer service was wholly uninterested in providing any kind of assistance, so it's presently a paper weight maybe awaiting future resurrection or dissection as the case may be.
The notable exception being 240V thermostats mainly used for electric baseboard heaters. A friend of mine has a house with electric baseboard heaters and a thermostat in every room. Electricity must have been real cheap when it was built in the 60s...(the house also has central AC/heat pump so that is what is actually used for heating).
@@brianleeper5737 Mid 70's the local electric company had a big push to install 240V baseboard heating, they offered the units and a big discount on power if you switched. My folks went for it and had them in every room. Winter time the power meter sounded like it was ready to orbit. About 3 years later all of the perks vanished and they became $$$$$$$ to run.
The 240v supply isnt generated by anything, its supplied by the same 240 the furnace uses. People seem to stuggle to understand the US is 120/240v (110 / 220 whatever)
@@AnIdiotAboard_ Andrew Fremantle wrote *24V*, not 240V.
Loved the "unprofessional" disassembly of the capacitor. Makes me want to try and make a DIY one.
I have one of these in my “to fix” pile for my dad - what a coincidence. He tried to get the power supply module replaced from the company (based in Blackburn I think) but they said they don’t have any left and it’s discontinued - not much help when you’ve got a large building full of them. Fortunately had our own spares but I’d like to fix the dead one knowing there’s no chance of buying more!
I do like a good fix video. Great instructions for folk running things like Repair Cafe events. 😃
Oh yeah, definitely a good warning to make sure you always unplug live mains stuff when you're working on it. Just the other week I swapped out a bulging cap, and the plug was a bit stiff when I went to test it with the lid off the device, but instead of unplugging the cable from the mains and plugging it into the device properly, I went to get a good grip on it and ended up getting a good shock instead! I don't think it was the full AC mains since it didn't hurt too much, just enough of a zap to make me knock it off the table.
I have to remember not to do work on mains electronics after a 12 hour day at work.
Many years ago I got a full-strength mains shock across just the width of one finger (here in North America, so it was nominally 120V). I hardly felt a thing, mostly I just felt the parts of my finger that were making contact feeling like they were vibrating. In fact, that was the ONLY thing I felt from the zap. I didn't realize I was getting a shock at all until I looked to see what was causing that strange sensation as I was trying to pull a plug out of an outlet and there I was, with a finger against both pins.
@@evensgrey For me it was definitely more than that, it felt like someone had slapped my hand moderately hard.
It's been properly Rogered when removed from the case :)
Been waiting to use that one...
I love these repair videos, I repaired a defective 22" monitor (white screen) by replacing two capacitors, inspired by your videos! Keep them awesome vids coming!
Yesterday I spent some time attempting to de-solder a couple of transformers from one of those dimmable fluorescence light bulbs.
My intention was to see if one of them could be used in a high voltage inverter circuit. The PCB was packed with a remarkable number of both leaded and surface mount components.
Unfortunately all the components were held in with lead free solder that appeared to only melt well above 400C. Despite using all the tricks, solder sucker, hot air gun and two soldering irons, solder wick, I gave up after an hour.
The transformers have five pins, which fitted near perfectly into the very well gold plated through holes. The solder had wicked up on the connections to make them look top and bottom soldered, and to add insult to injury the transformer pins had obviously been bent over during assemble, ensuring they would not drop out when all the pins were heated at once with the hot air gun. I suspect that the transformers were also glued to the PCB.
Individually melting the solder on each pin was an exercise in futility, as the lead free solder re solidified as soon as the iron was removed from the joint. Because of the tight fit of the plated through holes, solder wick and the suction gun could not remove the solder on the sides of the connections.
I tried diluting the solder with the lower melting point lead/tin but that did not work. I have to conclude that some products are just not made to be disassembled for salvaged. Did I mention how much I hate lead free solder.
For pulling smaller capacitors, one of my favorite tools is larger sized cross-lock tweezers. Specifically they seem to go by weird names like "orthodontic debonding posterior bracket tweezers" but the one with the tiny little flag shape that looks more like a lock-pick and has a weird bracket sticking out the back end of the handle. It has serrations and really keeps things from slipping away!
I bend them left, then flow the solder until it pops out a wee bit, then do right, and so forth until it pops out.
I sometimes just ripped the cap off with some pliers and desoldered the legs off afterwards :)
@@Qwarzz Ya. I did that, too. But was too ashamed to admit because it seemed naughty. Maybe it is, but at least i am not alone ^^
@@ChrisBigBad It does really help with the larger caps as there will be less mass to be heated then.
Amazing how quickly you identified the failed component .. great work
My favorite type of BC video :-)
It is common practice to put multiple diodes or resistors in series to improve safety in the event of a failure mode. If one fails short circuit, there is still another to take its place. However if it did fail short circuit then it becomes a dormant failure which is not ideal.
Recently had a VFD that had been sitting around a while pop its caps. Learned about reforming.
_"Julian Ilett Blu-Tack"_ 6:27 LOL. Yep, Julian loves his Blu-Tack.
Might've been interesting to see what the ESR of that faulty electrolytic capacitor was, prior to disassembly.
I have fixed my dvd recorder by replacing 3 domed capacitors, enjoyed watching you remove the capacitor.
Hearing you speak about how things can blow up when we're not paying attention -- and will happen at least once to everyone -- makes me realize I'm not the electronics klutz I thought I was.
I've noticed that some electrolytic capacitors are a bit sneaky and don't some their tops at all, which makes the faulty ones that much more fun to find. I've even had people say "Oh I noticed that, so I just pressed it back down again" 🤦
I've seen them lift off the bung rather than dome the top. Doming isn't a 100% foolproof test (every domed cap is buggered but not every buggered cap domes)
@@miscbits6399 That is absolutely true. I discovered that when working on a Dell PC motherboard, populated with hundreds of those horrible green electrolytics. I ended up swapping about half of them, just to find two or three duds. The domes failed to rise to the occasion.
Me Da and later me lad and i have always opened up dodgy electronica to see if there was something simple enough to fix with a soldering iron and four ham fists.
Not fond memories of the first gen Rank Arena CRT colour telly (crackle, AAAARGH) but we've managed to get lots of other things back up and running. It's nearly always a popped cap.
It's also good fun heads down over the dining table discussing how to pull stuff apart without causing permanent destruction.
Thanks for the happy memories big feller :)
Clive! I am sure you realize we are all waiting for the dry you goof and something goes BANG. From your video's I really do think you would upload it. Thanks for all your work.
Unfortunately, if the bang is big enough Clive will not be in position to upload it! Maybe he should create a video called "In the event of ..."
Very good, Clive. I enjoy these fixer upper videos .... and the catastrophic failure analysis ones .... all of your videos ....
I recapped a failed industrial PLC power supply the other day. It worked afterwards.
I measured the suspect caps with an LCR meter. One of then measured 1.9KΩ @120Hz, couple hundred nF
Cheap gemmy 'gemcon' brand. Replaced with nichicons.
Overall the PCB was nicely engineered - other than a failure to design in some thermal pads to floods -- with very small vias.
8:00 reminds me of when Clive did the high voltage test and I couldn't stop laughing when he said "Fucking hell".
What video was that from?
A very satisfying repair vlog.
I also had one of these fail and again a capacitor replacement fixed it. The PSU has no airflow which i assume is due to safety requirements. So i drilled some small holes in the bottom and top so it at least can breathe. May reduce operating temp a few degrees which in turn will give it a longer lifespan.
The plastic backbox holding the power supply, now has ventilation slats in it.
Using better-quality electrolytic capacitors is crucial. Avoid stuff from China. Better choices are Japan or Taiwan. "Domed" electrolytics are a common mode of death for computer motherboards that source these parts from China.
@@Milosz_Ostrow
The secret is keeping them cool.
A great component for planned obsolescence, the electrolytic capacitor.
It isn't necessarily planned. Sometimes you just get bad ones. Sometimes entire production runs are just bad and have abnormally short lives. This was a HUGE problem for a while between 1999 and 2007 due to bad electrolyte formulations from some manufacturers, particularly in Taiwan. The affected capacitors failed so frequently it was known as 'Capacitor Plague.'
That was a quick fix. This year I learned more about capacitors than ever before. I think capacitors are most responsible for defective electronics at all.
To make desoldering more easy I bought a cheap ADT03 "sucker" from my favorite Ali in china and I can recommend it. There are reviews on youtube.
I think its down to the use of cheap Chinese capacitors, as well as potentially exceeding the RMS ripple ratings on the little shit capacitors used for the bootstrap circuits. That was a common theme as well back in the 2000's when the first high current processors like the AMD Athlons spawned the need for high current buck converters on the boards, with the need for low ESR capacitors. Not unsurprisingly the cheap Asian capacitors all went tits-up. Having built my own SMPS' I can say that those low ESR capacitors are touchy, and can be destroyed instantly if you exceed their ratings or die a slow death from heat exposure. That said, using good 10,000 hour Japanese capacitors along with ensuring the ratings are not exceeded seems to provide good reliability thus far, but these are too expensive for the profit strapped companies in the consumer market. Kind of sucks as my parents just tossed a large flat-screen TV due to a failed bootstrap capacitor in its internal power supply. I knew what the problem was, just did not have the time to fix it for them.
Electrolytic capacitors have been the issue with a lot of older failed electronics I've worked on. With computer motherboards, displays/TVs and basically any power supplies.
This is fortunately often easy to spot like it was here as well.
Mount the board then get yourself some Kelly Forceps. You can grab that nice and strong. Always nice to have a selection of hemostats. They are not just for the medical industry.
What a coincidence that you posted a broken thermostat as I had a thermostat "issue" last week. My Nest stopped turning on the furnace. After checking wires, running a new Common wire, and also restarting it, tests showed it COULD turn on the furnace in the equipment test mode, it just would not do it normally. I went through 3 days of a very cold house until I finally called Nest support. Turns out they had done a firmware update just that morning that apparently had caused it to THINK it was turning on the system but it really had not. A factory reset, and reinstall in the Nest app finally fixed it.
The era when we have to convince our tools to work has come.
Don't you just love it when a firmware update leaves you on the cold? What a time to be alive...
This failure mode is very unlikely with my system, as it’s air gapped (meaning it does not have an internet connection) 😀
@@Mark1024MAK It's even more unlikely with my system, as it's just a bimetallic strip and a mercury-style switch. I know they used to use real mercury switches, but this was made in the 90s so it's probably a different technology of tilt switch.
@@eDoc2020 and @Mark 1024MAK - I hear you but being connected has advantages. For example, during the recent California fires, while we were evacuated, I could check the Nest from anywhere to see if was online and check the temp inside the house. It let us know the house was still there. Also, it is nice to be able to just say "Hey Google - temperature up" if things are getting cold.
Definitely up for more of the fixing stuff. Fascinating.
Dry Capacitors, Juicy Solder: the Big Clive Story
"What's Grandpa doing out there, running through the snow?" "Uhhh... It looks like his electric socks are on fire."
8o] 🔥
Talking about playing about with electronics and mains voltages ... I was working late on a faulty PSU a few months ago in a prominent building in London. I had to swap out the switch mode PSU for a lock which just wasn't supplying the full 13.8 volts (12 volt nominal) under load. It was running off a UPS as was the network switch which itself also was running two cameras and the access control panel. I clearly wasn't paying attention and put green and yellow where brown should go and vice versa. All nice and tidy and sound, I plugged the "kettle" lead into the UPS socket and there was a loud bang. Suddenly nothing was supplying anything. The fuse in the spur blew, the breaker behind it locked away in a riser somewhere unknown to me tripped and the UPS turned out not to be as uninterruptible as expected. Fortunately, a knowledgeable resident electrician was available and he just said "oh well, that's what breakers are for", reset it, I corrected my connections, changed the fuse and breathed a sigh of relief when it all worked on power up.
Thanks for the tip on using low ESR caps in switch mode circuits.
Such awesome content from big Clive!
Excellent! Thanks, Clive. 🤗👍😍
I'd like to see you do like the 5 minute crafts videos do. They wave their hand over the length of wood and voilà! It's cut into four pieces! 👍
DE-soldering trick has been my favourite for years.
Another great fix :D Your videos on caps allowed me to mend my mums doorbell. That was a dead class X cap which I replaced with a value slightly lower (all I could get) and its happily still working :) Don't think I've experienced anything randomly squirting its juice all over my hand yet, but there is still time ROFL 🤣
Thank you again BC - always helping me/us learn. Stay safe Bro.
Thanks for this Clive, I fitted one of these a few months ago and while it's fine at the moment I'll remember this (hopefully!) if it dies.
Another great video Clive!
“Because we can”. That’s what I like to hear.
Clive you are the man 👌🏼 from BIG fan from Surrey 🇬🇧
I'm Mr. Green Christmas, I'm Mr. Sun.
I'm Mr. Heat Blister, I'm Mr. Hundred and One.
They call me Heat Miser, whatever I touch,
Starts to melt in my clutch.
I'm too much!
Thanks. I now understand why my new thermostat only lasted 5 Days.
I heard they put several diodes in series as a crude measure of protection, because power diodes tend to fail in short-circuit. This won't protect the third time, however.
Had a bunch of 1N4007-13 diodes fail short. 1300V rated, lightning does amazing things.
Regulations require tolerance to 2500Vpk 8/20 us transients on 300V CAT II appliances, while you can absorb the transient with series RL and parallel C, your diodes have to block that voltage if it comes the other way around. This is not an issue with a bridge rectifier, but with a half wave rectifier this has to be done.
If I had to guess, they used diodes with a low maximum reverse polarity voltage of 100V, so 3 in series gets them to 300V which will work.
@@edman007x That is a stupid idea. The cost of making a 1000V diode is no more than that of a 100V diode. A diode with higher voltage can share the same construction, just with lower doping concentration, so that it has a higher barrier height (hence higher Vf) and a lower carrier concentration in forward conduction mode at a given current (hence higher dynamic resistance). For a low current application like here, the cost difference is negligible.
@@edman007x Also for those super cheap parts, the package (copper, plastic, etc.) is certainly more expensive than the chip itself, and the bigger elephant in the room is the scale of economy. Everyone uses 1N4007 for mains voltage and 1N4001 for low voltage AC, that's why you can hardly buy 1N4002~1N4006, and even if you can, they are likely to be more expensive, and anyway you will just get the same ones as their higher voltage counterparts. Right from the manufacturers, they will only make maybe 3 voltage levels, and they will rebrand them as the next lower voltage parts to save logistics cost. If you read datasheet of those parts, particularly low cost parts, you will find the adjacent two parts have the same rated Vf, same Trr, and pretty much same everything, other than max voltage, and the lower rated one might actually be more expensive from distributors.
I've just moved to a house with about a dozen of these thermostats. I'll keep this video in mind if any of the displays suddenly fail!
A dozen thermostats.. must be some kind of mansion. I'm impressed when someone has a separate thermostat for upstairs lol.
@@akunog3665 Our old house had two, one for bedrooms and one for the downstairs that I switched out to a hive.
New place was built by a gas engineer, the plumbing is a work of art but I'm still figuring out the app!
In my days as a comms tech we had a lot of issues with a certain brand of caps, we had special gear to keep the power on modules while we removed them to bridge another cap across suspect ones, any interruption to power and the damn things would start working again, for a while..
Lead-free solder, as far as my little brain can understand, is horrible for appliances too: it makes them fragile, and it provokes overheating when you want to fix them at home.
Oh, you just used the «give it a flick» technique of desoldering, I found it is a useful method sometimes.
And thanks for another interesting video!
I only work with lead free solder. My JBC Nano cartridges are sensitive to lead and lead promotes plating layer dissolving rather quickly. Over the years I think now I work better with SAC305 than any other solder.
That was excellent, cheers for sharing!
ANOTHER BRILIIANT REPAIR !!!!!!
Love the content Clive! 👍
‘Turn a camera on, everything will go wrong’
A maxim Ms. Zapruder might have considered before lighting up that Super 8.
Must have been the "foof foof valve"... :)
Thanks Clive ;)
My favorite capacitor failure was in a laptop, I think Acer or Asus, and it was one of those miniscule ceramics. I was diagnosing the computer for no power for a customer, and every time I hit the power switch I would hear a distinct pop before the system would power off. I removed all the plastic covering so I could see the bare board to look for any visual signs of failure. When I hit the power switch, I found out that distinct pop was one of those little capacitors spewing sparks as much as 7 centimeters high, and upon closer inspection there was a crack in it. Someone pointed out that the capacitor was wired redundantly and the system could theoretically work without it, and they suggested giving it a little flick to break it off.
I did that, and I only had to touch it for the thing to shatter and fall apart into shards almost as fine as dust. The system worked perfectly normally afterwards, it seems what the capacitor was doing was just causing a short/power surge of some kind that caused the system to power off.
Multi layer ceramic caps like to fail short. They consist of dozens of very thin interleaved ceramics with a conductive coating. If they crack, they tend to short circuit between the poles. Hence by removing it, you removed the short and the power rail was no longer pulled to ground. May cause stability issues, but you never really know.
@@kain0m Makes sense. I remember telling the customer that it was working but not to expect longevity, so that much was covered.
Ah, a redundant failure point! Always good to have one extra in case the first one doesn't fail.
@@Gameboygenius honestly it's more likely it's like that to meet a current specification. This was on a power delivery circuit so there were many rows of this, and it probably was just able to take losing a capacitor and still be able to supply enough power to the system under most circumstances.
@@VraerynDaDragon it was sarcasm. "The manufacturer designed it with as many failure point as possible to make sure it failed."
Fine repair sir!
Electrolytics in switching power supplies are not your average run-of-the-mill capacitors, and for good reason. If you study how an off-line switcher like this works, you find that most of them are flybacks. That means the primary conducts current while the secondary is off, then on the other half of the cycle it reverses, where the primary is off and the secondary is off. The secondary current is either a triangular waveform (starts at zero, jumps to some large value in an instant, then ramps down to zero) or it's trapezoidal in shape.
The key takeaway is that the AVERAGE of either of these current waveforms is the DC output current. If the DC output current is, say, 1A, it means the peak secondary current is quite high, maybe 4-5A. This current is dumped into the output filter capacitor, which is actually an ideal capacitor in series with the capacitor's Equivalent Series Resistance (ESR). A generic electrolytic has a very high ESR, several ohms; a switching capacitor has, by design, a much lower ESR, ideally in the milliohm region. The large flyback secondary current waveform hits this ESR, and as everyone knows, you then get I^2*R power loss in the ESR resistance, which produces heat. Heat is the mortal enemy of capacitors because it dries them out. This is why the usual failure mode in a flyback switcher is the output filter capacitor(s) - the capacitor simply dries out.
For the budding EE out there, draw a triangular waveform that has a 50% duty cycle (just guessing that), and a peak current of Ipk. Draw in a horizontal line through this waveform and call it Iout. The equation is Iout = Ipk/2 * 0.5, the area under the triangle for the entire switcher period. As you can see, Ipk = 4*Iout. The same sort of stresses apply to the primary filter capacitor. Conclusion: flyback switchers stress the dickens out of their capacitors.
It took you all that text to say that the capacitor gets charged with a very short duration, high current ‘spike’ 😀
@@Mark1024MAK And it took you one short sentence to say 1) I have no desire to learn anything, and 2) I didn't understand anything you said anyway. There's a reason textbooks are a few hundred pages thick, not a series of one-sentence ignorant statements of "stuff."
@@demef758 - Absolutely right that educational text books go into great detail. As do education courses about electronic systems and technology. People should always endeavour to be open to learning new information and develop new skills.
This overheating was obviously a problem. 0:55 The plastic backplate with the writing on it, now has vent slats in it. That one is fully enclosed in plastic giving *no* ventilation. A bad initial design for the plastic enclosure, which Heatmiser have rectified. The electronics appear to be more than good enough.
If you have an old one like this which is solid plastic, drill small holes in it, especially top and bottom. *Recommended.*
They fit into a standard, electrical, single, 35mm deep, backbox. Best to have a metal backbox to dissipate heat. *Recommended.*
This goes for any other make of timer/stat that fits into a standard single backbox.
If it's not the capacitors, it's the capacitors, cos it's always the capacitors, even when it's not... :P
except when its a shorted diode.
Or a dry joint… or a broken wire…
Why did I stop breathing when you were trying to put the white cover back on the repaired module? :-X
Anyway, great to see this done; I have a very similar Made in Guess Where thermostat which might need the same operation in the future...
how is this 2 weeks ago
@@ThatVoxelBlock It was probably already available for Patreon supporters.
Satisfying when I fixed a tv by replacing 3 domed caps on the power supply.
No joy with a touchscreen thermostat that lost its touch. I got it working 3 times by cleaning the connections of the 4 wires, but it kept going nuts. Likely corrosion that got migrated to the otherside of the board underneath the LCD. Used it until I had to interact with the underlying thermostat function to change it to heating when I popped in a replacement.
Electroboom moment,"Finger test, it's dead".
There's a very common problem on vaillant boilers where the water temperature on the display fluctuates quite wildly. This is due to 2 electrolytics failing. You can always tell because if you take a hairdryer to them and warm them up, it fixes the problem until they cool back down obviously. It's because the voltage to the water temperature sensor has become unstable I believe. It's a very common problem with these boilers that use this particular control board which most of them do.
Hmmm "jooseee solder" haha what a turn of phrase I'm luvvin' it!
Amazing how a device that has not changed in hundreds of years causes the majority of faults on electrical items and sends them to landfill for the cost of a 25p component!
Bit like all those Led tellies you see at the Cowp all junked for the cost of a 50p Led - If only they wired them all in parallel eh
Built in obsolescence or am I being cynical lol
Just fixed my 10 year old Indesit washing machine - fault - two 25p capacitors!
Hopefully that's another 10 years use!
I have this model of thermostat for a heated floor, good to know there is possibly a fix if it ever goes dark.
"...the pressure's built up and it's basically vented all its juice out..." *snort*
I was so hoping at the start of this you would rip open the capacitor so we could see inside, thanks for not dissapointing me !
Now wash your hands children !
That one person that disliked this video is really sad
They just couldn't capacitate it.
"Finger test!"
😇 Clive you are brilliant haha
Ha! I just had one of these installed, controlling my heated flooring - Heatmiser Neostat-e - with the external sensor being under the floor. At least I know what to look for if/when it dies! It's a neat little unit and with a Neohub it has Homekit integration too. Nice to see it here!
Awesome. Hope you have it wired into the network so it can easily be shut down remotely when they feel you've exceeded your carbon allowance for the month.
I’ve got a bunch of these Heatmiser stats. I’ve done the exact same fix on 2 of them so far. Other than that, they’re pretty robust and work pretty well. Just could do with a better quality lowESR cap in the first place.
Good to know, we have these in every room so will be prepared if they die. As the PSU is a separate part it would be good if Heatmiser sold them separately.
Always remember the inspector at Plessey with stcky fluff on his glasses when the top of a capacitor blew the safety cross "X" and shot the contents up into his face.
Hi, many thanks for the info and entertainment.
The capacitor is dead.
Long live the capacitor.
They really went to town as well with plating those tracks so the end user can't blow them off as easily. As stated elsewhere here in the comments, in the US the thermostats run off of 24V DC, and just have small signal relays in them to tell the air handler what's being called (heat or A/C + compressor), and all the heavy lifting is done in the units themselves with usually 50/60 Hz transformers providing the needed voltage and then large heavy contactors for switching. Makes sense since it ensures that home owners and HVAC techs wont be exposed to mains voltage unless they are inside the units themselves, and they're quite reliable in that configuration. Odd to see a place like Europe with its extreme safety culture using mains voltage at the thermostat.
Yeah, but our thermostats are usually controlling heating systems. In the U.K. not many homes have air conditioning. The thermostat either directly switches 230V (240V) mains electrical heating. Or controls a 230V (240V) feed to a gas or oil fired boiler, and/or 230V (240V) water pumps or water valves. As the entire central heating system runs at 230V (240V), there is no low voltage supply to use.
@@Mark1024MAK That's what I figured since the construction is so much older, not to mention the cultural differences. Here in the US most of the homes were built in the years after WWII, so things tended to be a bit more modern. It's very much like my grandparents farmhouse I used to go to for the summer as a kid. They had coal heat and only a telephone and radio until the 90's. "Want a hot bath? Go shovel the coal yourself" my grandfather used to say. And some shoveling and 45 minutes later, you had hot water for _one_ bath.
In my US furnace the thermostat contacts pass all the current used by the gas valve, as I believe is traditional. In the true older style systems the blower would be controlled by a mains-rated temperature switch on the heat exchanger, although on mine it is electronics and a relay. So our thermostats aren't just switching small signals but actually a good portion of an amp. Of course newer furnaces probably don't pass that much current but generic thermostats need to be able to carry it.
@@eDoc2020 Obviously by small signal I mean low voltage and relatively low current to just run solenoids in the contactors. Not like what you would find in an RF receiver for routing the incoming signal around. There are mains ones as well in very old simple systems, but these were usually mercury bulbs that would turn on a blower directly. Usually had these at old apartments that I stayed at in college and such. Fair amount of mercury in those, and that stuff just disappears in carpets when you bust them. I accidentally broke a blood pressure cuff bulb in my dads office that had a good few fluid ounces of mercury, and it just went "poof" as soon as it hit the carpet. No idea where it all went.
Your talking about the frequency the capacitor on the low voltage side made me wonder if that capacitor would have lived a longer life if it had a bridge rectifier before it in either a single package or 4 separate diodes.
Thanks so much Clive. You mentioned "about five for £1". Is Farnell the best/easiest option for these capacitors? As I really need my hand held, have you a part number?
Top work, Clive. :-)
standard electrician prank: exploding a paper bag behind someone as they plug items in (less likely to result in disciplinary action than meggering the trainee)
great fix
Funny what you said about the VFD. I had a laser do that to me after repairs.