Portable induction hob

[KawasakiKen]

Hi,

I have a little electrical knowledge and hardly any electronic expertise!! I have a 2nd-hand portable induction hob (plug-in 13A), which worked fine for several months but suddenly blew  the 13A plug fuse and tripped the ring main circuit breaker in my consumer unit. No smoke or smell, and I have removed the circuit board and there is no sign of any blown components or tracking, but the ceramic fuse (F1 - soldered onto board) is open-circuit.

I can't do anything more, and am trying to find out whether it's worth pursuing, and if so how, or where, I can find someone to investigate it? I live in Truro, Cornwall, UK.

Any comments, advice most welcome!

Cheers, Ken

[capt bullshot]

The internal fuse in such stuff is "last resort to prevent a fire starting" only.
So I'd expect that thing to just blow the fuse again in case you replace the fuse only.
As a wild guess, I'd think the main power semiconductor (usually an IGBT) has turned into a short, causing the fuses to blow. This in turn can have various root causes, including the IGBT just decided to turn into a short because it can (often due to poor thermal design). Anyway, there's also a resonant capacitor that might have degraded over time, causing the IGBT to break down, and some more possible failures.
You might be lucky by swapping the fuse and the IGBT, but it just could blow up again.

[BurningTantalum]

Could you post some clear close-up pics of the PCB?
BT

[KawasakiKen]

Thanks Capt bullshot,

In view of your helpful (but over my head!) suggestions, I'm thinking the cost of me getting anyone to look at it, if I can even find someone, means I am probably better off buying a new one!

Cheers,
Ken

[KawasakiKen]

Thanks to you also Burning Tantalum,

Taken some photos, but can't see how to post them...and bearing in mind my reply to Capt Bullshot, I guess there is no point, do you think??

Cheers,
Ken

[stevelup]

I’d say not worth bothering considering you can replace it for less than £30

[BurningTantalum]

Stevelup- This is very true, but I refrained from telling Ken that these units are available at my local Kmart for AU$49 in the hope that he would have a go at repairing it. He, and we, would learn something and have some fun at the same time.
This is, after all, one of the reasons we lurk on this forum.
Regards, BT

[tooki]

Thanks Capt bullshot,

In view of your helpful (but over my head!) suggestions, I'm thinking the cost of me getting anyone to look at it, if I can even find someone, means I am probably better off buying a new one!

Ikea has one for 35 quid: https://www.ikea.com/gb/en/products/kitchen-products/appliances/hobs/tillreda-portable-induction-hob-white-art-40331630/

So yeah, not worth fixing, sadly.

[drussell]

Sometimes there is value in repairing something beyond the monetary value saved over buying a new one.  Often this is simply that you get to learn about how something works, increase your knowledge and feel some satisfaction in having fixed something yourself.

In this case, sure, he can just replace it, but if he has a multimeter it is at least a chance to learn some basic electronics troubleshooting that might be useful in the future, perhaps on a more expensive item.

Even if it isn't worth fixing from an economic view, it is still interesting to know why something failed.  A few simple checks with a multmeter would at least confirm that the IGBT is shorted, for example, (certainly the most likely direct failure) even if KawasakiKen doesn't decide to actually fix the unit.

[KawasakiKen]

Hi guys, thanks for all your replies...especially drussell with your philosophical input - you've inspired me to pursue the investigation (despite only having a miniature soldering iron, no de-soldering wick or solder, a very basic multimeter and very limited component fault-finding expertise!! (e.g. how do I check the IGBT for short, and do I need to remove it to do so?).

Tooki's and Stevelup's suggestions also struck a chord, although my previous two Judge-badged purchases of hobs from Mallets Home Hardware, costing 49.99 each, only lasted a year each and both failed with the same fault!!

 Don't know if the photos are any help??  If I get stuck, do any of you fancy a holiday in sunny Cornwall, UK...I can accommodate you!!

[Zero999]

The thing screwed to that piece of extruded aluminium (heat sink) is the IGBT and the black box nearby appears to be the resonant capacitor. If you unscew the IGBT from the heat sink, hopefully it will have a part number written on it, allowing you to find the data sheet and a replacement.

[KawasakiKen]

Thanks hero999, have lifted heat sink off, but would like to check IGBT for short....can I do that without removing it, and which legs do I meter, please?

[Zero999]

Thanks hero999, have lifted heat sink off, but would like to check IGBT for short....can I do that without removing it, and which legs do I meter, please?

If you can ascertain which pin is which, by Googling the part number to get the data sheet, it can be tested with a multimeter.

[drussell]

I would also check that bridge rectifier that is under the heat sink with the IGBT.  The typical failure mode for rectifier diodes is also a short, like it is for power MOSFETs and IGBTs.

When in diode test mode, your multimeter should show a diode drop (about half a volt) across each diode in one direction only and show open circuit in the other direction.  (You will also see TWO diode drops, about 1 volt, across the series sets of two diodes if you test between the two AC input terminals or the DC output terminals.)

I'm sure someone can point to a good tutorial on bridge rectifier testing better than I could explain it... 

Because your unit blew fuses, we suspect a dead short in one or more of the main power handling components, a filter capacitor, etc., anything that would end up essentially directly across the power rails.

[bson]

You need to know what part it is to know the pinout, which you need to know to check it.  You'd check for continuity between collector and emitter (there should be none) and that the B-E and B-C junctions look like diodes - so will have specific forward voltages.  But you need to know which pin is which, and although you could infer the pinout from the board traces eventually you'll still want the datasheet for it.

In general however, given this is a mains powered device with mains voltages in it, that has blown a fuse, and you have no idea what you're doing I'd strongly advice against trying to repair it.  Just buy a new one, it's not the right kind of device to just go poking around in to learn...  Chances are you're just going to destroy the PCB in an endless cycle of fuse replacement as it keeps blowing.  Or end up doing something inherently dangerous like short out the fuse terminals or use alligator clips because repeatedly esoldering it is tedious and damaging.  Or knock it off your bench and into something, like your lap, while powered.  Not worth it.

[KawasakiKen]

Thanks bson, I think I am going to take your advice...I've just wasted a good hour or so trying to find a match for the IGBT H20R120, and its datasheet, and bridge rectifier D25SB80 without success, and although find similar-looking ones, I don't know the ratings of mine so am really out of my depth (without even solder braid or vacuum puller)!! Besides, I've just acquired an old piano accordion with broken keys, springs and dampers, but no ac mains to kill me, so perhaps I'll stick with that, as my next project,

Thanks to all you guys for your suggestions and time.

Regards,

KawasakiKen ('98 ZZR600)

[BurningTantalum]

First PDF hit on Google:
https://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=8&cad=rja&uact=8&ved=2ahUKEwip7-HJj7LdAhXkh1QKHTdgAY0QFjAHegQICRAC&url=https%3A%2F%2Fwww.infineon.com%2Fdgdl%2FInfineon-IHW20N120R3-DS-v02_06-EN.pdf%3FfileId%3Ddb3a304320d39d590121819187cb19a8&usg=AOvVaw06PyzascHBVbLAguSVh2F6

I would at least poke a meter at the IGBT without removing it from the PCB. The same with the bridge.
Chances are the device will have gone dead short across at least two pins, The gate pin to the others should be open circuit or close to it depending on what is connected to it. If dead short I would remove it to test out of circuit (you will have to remove it anyway to replace it)
The bridge is even easier but is likely to be OK. Diode test range; Red lead to the AC pin and black lead to the + pin should show around 600mV. Repeat for the other AC pin. Black lead to the AC pins and red lead to the - pin should give the same reading.
I have just repaired two induction units and both worked after the IGBT and fuse were replaced. As the units were not really of great value, I went against my judgement and ordered the semiconductors from China for a couple of dollars. Both units are still working fine.
If an IGBT and fuse doesn't fix it then toss it in the bin. You don't need to get anywhere near high voltages to achieve this. Just remember to put on safety glasses when it is powered up and not in a case.

2 Quid for 2 items:
https://www.ebay.co.uk/itm/2PCS-IHW20N120R3-H20R1203-TO-247/401474964181?hash=item5d79c5cad5:g:TOIAAOSw8RZaWAWe

Sorry to hijack your thread after you wanted to close it !
Regards, BT

[KawasakiKen]

Thanks bt,
Dead short all pins both directions! BR seems ok, so ordered IGBT as you did, and just waiting for slow boat from China. Need to rummage around to see whether I still have my spring-loaded solder sucker!!

Cheers,

Kk

[drussell]

Dead short all pins both directions! BR seems ok, so ordered IGBT as you did, and just waiting for slow boat from China.

That is as expected, for the IGBT.  Usually when they short, it is obvious.  Even without a datasheet it is usually easy to tell when they've blown their internals to smithereens.    What you will need to check, though, once you dis-mount it, is whether it is really only the IGBT that is shorted or whether there is another short on the board also.  (Unlikely, but check anyway that it is really just the IGBT that is shorted.)

The recitifier being OK is not a surprise, either.  They can take very high peak currents for a short time and survive.  A 1N4007 1A diode can handle instantaneous peaks of 30A or something silly like that and the 3A diodes generally 50-60,  Bridge rectifiers rated in the 10-15 A range can usually handle surges in the hundreds of amps and still survive.

Need to rummage around to see whether I still have my spring-loaded solder sucker!!

I hate when I can't find a solder slurper...  Especially since I have about 6 of them. 

[drussell]

Also, be sure to use the correct rating and type of ceramic fuse.  If you can't easily find a pigtail version of the fuse, wire in a proper fuse holder, don't bodge it!    if the unit doesn't work in the end, you can always salvage the fuse holder for your parts bin.

(If you don't have a parts bin, well...  you should.  )  You can also save the bridge rectifier, any relays, the inductors, etc. but I have a funny feeling it is going to Just Work once you replace the IGBT and the fuse.  If it doesn't, what did you waste, a couple dollars for IGBTs and an hour or two of your time as a learning experience?  I say that's still worth it.

[KawasakiKen]

Thanks for your advice drummell.....funny you mention difficulty finding fuse! Mine is a 250V 15A, 6x32mm, ceramic fast (I guess!), and I cannot find a supplier on line (or on telephone) in the UK who stocks any with pigtails, unless I buy 100 or more!!!

There is one in Penzance who has some 16A ones, or I can source same rating in 5x20mm size...will either or both of those be ok?

[KawasakiKen]

Sorry drussell...got your name wrong 

[drussell]

Sorry drussell...got your name wrong 

Heh...  No worries! 

You can edit your posts, you know....  Just click the "Modify" button that is in the upper right corner of a post, between "Reply," "Quote" and "Remove".

funny you mention difficulty finding fuse! Mine is a 250V 15A, 6x32mm, ceramic fast (I guess!)

That fuse is the standard 0.25 x 1.25 inch size, I believe they are called 3AB/3AG...  They are the same size as the standard glass AGC fuses, but a ceramic version.  I would think an induction cooktop would be slow blow, not fast.  You're looking for something like these ones from Digikey:

https://www.digikey.ca/products/en/circuit-protection/fuses/139?k=&pkeyword=&pv343=215&sf=1&FV=1c0003%2C403c49%2C403c4a%2Cc4004f%2Cmu15A%7C2088%2Cffe0008b&quantity=&ColumnSort=0&page=1&stock=1&pageSize=25

This search lists both the regular and pigtail versions with some model numbers which might help you have better luck finding ones near you.  Obviously you want to try to get the pigtail version if at all possible, but if you can't get those easily, you could also get a good 15A or higher rated fuse holder and wire that in so the fuse becomes more easily replaceable.

15A should be more common than 16A and normally you would never put a larger fuse in as a replacement but in this case, if you absolutely have to, the 16A would be OK.  Fuses aren't that precise and in these induction cookers most of the time by the time the fuse blows, the breaker is already tripping.  NOT preferable, but in this one instance, if you have to, it would still be OK.  A 13A or 14A would be a much better substitute since you're limited to 13A anyway on that circuit, right?

I'm not sure what electronics shops you have around you, but a 15A ceramic 250V fuse should be relatively easy to find, at least in the regular version.  The pigtail ones are always more difficult to find unless you have a well stocked local shop or industrial electronics supplier.

If I were trying to find one, even my usual go-to local industrial electronics supplier here doesn't stock them.  They have the regular 15A ceramic slow blow 3AG size, of course:

https://www.be-electronics.com/product_p/bk-fslash-mda15.htm

... and they stock the 2AG (5x15mm) size pigtail, glass, fast blow series, but nothing slow blow pigtail or ceramic pigtail of any kind.  I suspect you will have similar problems trying to source one easily locally.

Good luck!

[mariush]

I repaired one my parents bought a bit of time ago. Similar layout.

in my case, the fan got dirty and clogged with dust and oils and crap found in kitchen so it wouldn't move much air anymore, which caused the igbt to overheat and short itself out , which if i remember correctly also killed the bridge rectifier.  then it also went backwards through the igbt driver and a 18v zener diode and killed the switching regulator ic  (some offline switcher, viper series from st) that produced 18v for the fan and opamps (and then linear regulators made 12v and 5v for microcontrollers and other stuff onboard)

I replaced the igbt but couldn't get the 18v switcher working (probably some resistors or capacitors around it got shorted and was too lazy to figure out) so i just took a 34v switching power supply from an old inkjet printer and used a linear regulator to get 18v for the fan and the other voltages.

I suppose it gets a bit more hot than normal but it still works, months later.

[KawasakiKen]

Showing my ignorance here, but wouldn't a 5 X 20mm do the job, as long as the pigtails are long enough to go through the board?