Repair of Bosch induction cooktop touch controls

[francesco.comi]

First I would like to thank you, Otso and everybody else who helped identify and solve this issue.

I have the same issue with a Siemens cooking top with very similar controls, with a recently replaced glass.
After the glass replacement new buttons started to stop working.

I'm planning to do the same fix, but I have a couple of questions of how to exactly do the fix.

If I understand correctly I need a small wire (I have plenty) and I need to create a loop, put it on top of the touch button and solder it on one of the ends of the nearby resistor.

My questions:
- should I solder only one end of the loop?
- should the loop cross (I meed the two ends of the loop should touch at the end of the loop)?

Maybe I'm missing how the fix works...

I'm very practical with soldering, but never worked on this kind of touch controls.

Thank you for any help.

[francesco.comi]

I finally tried e succeded!

I would like to thank everyone who helped finding a solution to this issue!!!

I did the thin wire solution, it worked perfectly at the first try on every button I did it!
I used simple scotch tape to keep the wire attached to the button and isolated.
For some buttons I soldered near the resistor, on some other buttons it was too difficult to reach and used the via in the bottom. (Pictures attached for the first two I did)

For anybody with this issue, go ahead and do it, it is easier that what is seems!

Thank you!

[Otso]

The buttons have been working for me since I fixed them. However, after some time the cooking top has occasionally started beeping, similar to when you leave something on the top of the buttons. I wonder if they got oversensitive. When this happens, the only fix I have found is to power cycle the cooking top (by switching off the fuses and back). There are slight variations between how it behaves. Some, but not all, of the problems seem to occur when it has been hot for a long time.

[Fron]

Hello all induction repairers...

I read with lots of interest the communication about other Bosch induction cook plate troubles, so I ask your opinion about the following:

My daughter's Bosch induction cooktop (PIA645Q16E, 10 years old)  has different keys, I think infra red sender/receivers, and no problem there... But suddenly it made blew the fuse (house, 3-phase fuse of the cooking stove) and does not work anymore, even with fuse re-activated. I opened the cook-plate and found out 2 of the four IGTB's are defect. No visable damages but I measured them with an OHMmeter and the 2 left ones measure no values, the 2 right ones do..
I consider also exchanging the rectifier as I read this might have an influence too...

If someone can give me additional advice, please do so, as I have absolute no experience in this matter, only general 'mechanics' and all-round technical, mainly cars and medical equipment...

[Whales]

(Take this with a grain of salt, I have not worked on induction cooktops)

The IGBTs blowing might be a symptom, not a cause.  Other components may have worn out, perhaps there is a short in the coils or the capacitors have gone bad.  You might (?) be able to measure some of these problems with a multimeter.

[Fron]

Thanks for your super fast reply!
In the mean time I started to unsolder the defective IGBT's and rectifier, so I took out the main PCB and the back side did not look as 'nice' as the component side... ;-( I'l try to add some pictures.) Apparantly some fuses have blown with intense 'fire'-residues... These fuses (I assume that's what they are) have dissapeared and show empty burned tracks between some flat PCB-surfaces (wide tracks for high currents , I assume). As an unexperienced soldering guy, I don't think I can repair these 'fuses' (?) and even if I could, what is the value? It's a multilayer pcb.
So I think time has come to look for a new cook plate, nowadays available at about 400 euro's, the price Bosch asks for a new main PCB...

If someone can advise me the values of the 'fuses' and how to install them, please let me know. I might consider giving it a try.  On the picture, you can see some burned 'bridges' between the two white coloured rectangular zones. I assume that's where the fuses have burned...

[Whales]

Fron: could you please upload full quality versions of those photos to the forum by attaching them to your post?  Your external host (postimg.cc) only seems to have very small versions of the images, even when I click "Download original image", and I can't quite see the detail on some of the burned spots.  (Also image hosting websites inevitably die, many forum topics have become useless to readers because of this)

> These fuses (I assume that's what they are) have dissapeared and show empty burned tracks between some flat PCB-surfaces

Where do you see burned/disappeared tracks?  Are they the round translucent white rings with missing squares in the middle?  I have circled them in red:



These 3 marks are wired in series are look perfectly identical to one another, so I doubt they are fuses that blew during operation (but I could be wrong).  Perhaps they were factory milled/marked for some reason.  I am unsure of the function of those large rectangular copper shapes.

I can't quite tell yet, but I think most of the marks might be a combination of electrostatically attracted dust (brown) and arcing between exposed parts (black) possibly aided by the dust.

[Fron]

Hey Whales, OK, I put more detailed pictures although you're interpretation is correct. I mean the circeled (in red, by you) zones. The strange thing is that the other side (component side) of the print looks impeccable, as new. So the burn traces are really just on the back side surface of the board. I join the front side picture too. I assume the burns are 'fresh' and not due to dust accumulation by heath over the years. My experience is that such 'dirt' can easily be wiped off. Not on this spots...  It really looks to be caused by 'fire' or 'explosions'. So I assume some burned tracks. The white 'rectangles' are so imprinted on the pcb... Maybe showing the position of 'plates' in between the multi layers of the board?
The two soldering points top left of that rectangles (on the new bigger picture) is the mounting of a varistor on component side. This too looks 'as new' at component side! The location is indicated by an oval and the letters 'VR1'. You can also see the (now) open holes for the (dismounted) rectifier and one of the IGBT's?  So I was quite surprised by looking at the back side as my first impression when inspecting the component side of the pcb was 'notting visibly wrong'.
Quite bizar, that white rectangles, as if indicates the place where some component should be installed, but it is the back side of the pcb, and no 'fallen of' components found... ;-). I think it indicates the location of a 'plate' in between the multiple layers, and those where connected by the burned 'bridges' (?). So I'm afraid it's end of story. Even if I 'd find out the 'value' of what is missing (?) there, how should I solder it? To what connection?

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[Fron]

upload picture

[Whales]

Thankyou for the higher res photos.

Wow those 3 spots are indeed blown traces.  The copper has completely vaporised in 3 locations in series with each other.  There must have been a lot of continual high-voltage and high-frequency arcing.  Possibly the high frequency nature of the AC made it do a really neat and tidy job of milling away the copper?

The white circle are caused by the heat affecting the green soldermask.  I am not sure what caused the different smoke colours (brown & black), perhaps the 1st arc was a different temperature and size, then the others were smaller because of the higher series resistance of having to sustain multiple arcs.

Something is very wrong with your board if it was arcing for this long, eating away 3 different spots in series, all without stopping or complaining.  Possibly the entire high-power LC tank circuit is bad (bad capacitors?) or maybe the IGBTs were being driven too hard (bad sensing?).  I wish I could be of more help, sorry.

[Fron]

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Yes, quite a remarkeable burn spot, also on the back cover! I assume it must have been a strong 'spark' during the 'explosion'. I was not there when it happened, it is my daughters cooking plate. I think they heared 'a  noise' and the corresponding  fuse blew.
In the mean time it was decided to replace the cooking top by a larger one as the current has the problem of not enough room for several big size cooking pots. I wil (some day...) grind away the material around the burned fuses and see what's underneath. May be I can solder some wires as new 'fuses' (?- what value?) and of course replace the defective IGBT's and rectifier, and also check the capacitors...
Anyhow, thanks for the reactions!

[Fron]