Electronics > Repair
Repair of Bosch induction cooktop touch controls
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Klimfilt:
Hi all, unfortunately i'm writting here with the same problem... I have Bosch PXE675DC1E and first the timer button started to make troubles, but i ignored it because it's not a important key, but now the power button is dead and now this is a big problem. Im out of warranty so when i went to official bosch repair service, they told me that they don't service PCB and when client came to them with problem like this, they just buy new PCB... Yeah, 150 euros per 2 years, and after 7 years i will be paid the same amount of the induction hob, but this time will be only in boards... It's ridiculous and pity for Bosch company...

So now, how to resolve the problem. I saw 3 different methods to resolve problem. 1) to change the 74HC4053 chip , which accordingly to cell phone service technig would not help, because either the chip is working or not (i saw the post by Cozza) but if i tell him to do, he will do it after all. 2) to add copper foil on buttons (sensors) after i remove the glass, like Domini380 did and 3) to use isulation tape and put it on the back ot the glass, between sensors and glass, like Benneton sugest. So 2) and 3) method are close by same way, because both give advantage to increase touching surface and to make it more solid. Today we opened the hob and without the glas we touched the sensors directley and they worked, after that we used different cover for sensors (simple thin glass) and it worked just fine. But there is a logic in that, the chips to be gone because of the heat. And last one, guys from official Bosch service gave me 3 boards for free with buttons (sensors) and chips. I'm not sure that they are from the exact same hob, but visually they are the same (some have 2 large zons, other have more buttons) but in general they are the same.
So is it a good idea to use other HC4053 chips (not the one behind power button) and to install them on my board, or to order new ones from Farnell ? And will this even work, i mean to change chips?
Or to try to make touching area stronger?

P.S. Benneton do you have pics of your work ? And if not, can you tell where exacly did you put isulation tape on the back of the glass? Where the sensors make contact with the glass (looking my glass on the back, the sensors made their own nests), you mean to add tape there or ? I would be very greatfull if you add 1-2 pics of your job.
benneton:
Hi @Klimfilt.

Insulation is not above the sensors, but surrounding the spots. Just follow the pattern that was already there. I did take a picture from above (moment ago) and remembered that I also removed remains of old coating, too. See attached.

Will see to open it and make some pictures from the inside.

cozza:
Hi I would follow the advice of Domini380, as it's specific to the type of controller fitted to your cooktop. I cannot say whether the advice regarding adding the layer of insulation is relevant as it is a different type of hob.

I would try adding the copper foil strips to the non responsive buttons first and see if that solves the problem. If nothing improves, then replace the 4053 chip associated with the button. The copper strip on the button would connect via a piece of thin wire to the 4k7 resistor which feed into the 4053 input.

Let us know how you get on, I am curious.
cozza:
The problem with the Bosch touch sensors as Domini380 explained it is the connection between the grey conductive stuff on the button, which connects through a heat stake to a PCB pad, to the 4k7 resistor getting weak due to thermal cycling.

The easiest button to verify this with is the power button (no illuminated legend to cut around). Cut a square of foil the size of the top of the button (and leave attached a thin strip of copper foil like a wire to connect to the resistor).

Glue the square to the power button, solder the thin strip of foil to the 4k7 resistor ( the button side, not the chip side) and see if that solves the problem.



Klimfilt:
Hi all and thanks for fast responses. I'm sorry, but i'm not good at electronics (i'm an accountant...) but i like to resolve problems, not to be a consumer guy... So, please forgive me, but i didn't understand all that i should do :(. I'm attaching pics of my PCB, and what i did today and the how started to work (well not all sensors, but 85% of them are as new). When i removed the glass i noticed that the PCB lay on a black plastic base. This base is hooked to large metal square by 2 pinchs. When i touch the PCB it seemed to be very unstable and shakes a lot. So my first guess was that there is a "big" distance between the sensors and the glass. So i add some pieces of cardboard. After that PCB become a lit a bit stable and i installed the glass and when i tried the power sensor, voala it wokrs just like new one... But unfortunetley my joy was short when i figure out that not all sensors works. With this "invention", sensors marked with "1", "2", "5.5", "9", "boost" and two sensors for the large cook zone don't work. I know this is not a serious job and it's dangerous but it work and it's a some kind of a starting point. I will atach pics of my hob and what i did, but i didn't understand quite good the part with copper foil and where to put it. On top of the sensor (between the glass and surface of the sensor) or to remove the sensor from the PCB and to add it over the PCB and after that to install again the sensor on the PCB ? And what about the wire, and which resistor to connect with it? Sorry once again, i just need to be explained it like for a newbie or even a full noob with electronics. With 2-3 pics of the exactly what it should be done, may be it will be easy to understand. I will be very greatfull.

IMG1 - This is my "working" hob after my "invention".
IMG2 - This is the cover underneath the glass. Im not sure but i've read somewhere that this is some kind of silicium. @Benneton could you please tell me exact where i shoud add insulation. Can you point it on my pic ?
IMG3 - This is what i did...
IMG4 - How it looks after asembly
IMG5 - And it works ... Partly...

P.S. All sensors are working when i barely touch them directly (i mean when the glass is removed, like picture 5)
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