Electronics > Repair
Repair of Bosch induction cooktop touch controls
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srb1954:
I suspect that it is not just engineers that don't care about the design but also penny-pinching managers who insist on protection features be removed or components down sized to save a few cents.

I have had multiple problems with my Bosch induction cook-top due to under-rated components failing. Example: the reservoir capacitors on the main DC bus, which carry the full high-frequency ripple current from the element drivers, melted due to excessive self-heating from this ripple current. The original caps were polyester dielectric; far too lossy for use in this application. I replaced these with polyproplyene caps and there were no further over-heating problems. This was not so easy as the polypropylene caps were 3x the size of the polyester caps and I had to cut openings in the metal case for them to protrude through.
cozza:
"My questions are:
- Can a defective 74HC4053 still work with reduced sensitivity or is my missing/reduced sensitivity caused by another issue? 
- Is there a way to measure the good and bad ones with a multimeter? "

1 ) Yes, they can still work but be functionally impaired when damaged - one of the element selector buttons on my hob was like this. Weak and intermittent touch response.

2 ) No, not really.

cozza:
It's worth checking the mounting of the touch control panel, that it is as close to the glass panel as possible. I can't remember the mounting arrangement but some have the touch controls slightly sprung upwards on mounts to contact the glass.
Domini380:
Hi Cozza, thank you very much for the informative posting. It saved me a lot of time with the repair of similar touch panel. Let me add some comment that hopefully will save time of other people. In the past EGO used conductive rubber foam with a resistance around 100kohm that usually worked reliably and if failed then completely. The foam pads were glued to the PCB on the complete surface. The newer construction uses frame of conductive black plasic with transparent window and the whole element is covered with gray polymer. It is probably conductive but not measurable with simple measurement. They have patent on this where the construction is well described. The problem and design fail there is that only two diagonal corners are somehow attached to the board (probably thermal compression or conductive glue) and two more white non-conductive pins are just inserted in guiding hole. The top surface of the sensors is contacting transparent silicon compound to the ceramic plate surface (Ceran) and glues to this surfaces with the time. The thermal expansion of the ceramic and the board are different and the lateral forces will cause the sensor element contacts to break with the time. Unfortunately the new sensors are stiff enough not to relax the mechanical forces as the rubber foam was doing and the silicon layer too thin for this purpose as well. I experienced also that for each mounting and removal of the ceramic plate deteriorated the function of the sensors. With removed plate all sensors were working but some required some pressure that confirms together with deterioration after each plate removals  the hypothesis for bad contact. The solution was to attach conducting EMI copper foil stripes on all top sensor surfaces (just keeping the LED window exposed). There is 4.7k resistors providing some ESD protection. The stripes a left just long enough on the resistor side to be able to solder to it as the contact pads for the sensor are not exposed enough to be soldered. This solved the problem completely. I believe in your case the replacement of the 4053 the problem was solved not by the replacement of the IC but by the heating of the PCB. The multiplexer is just on the backside of the ON button and the resoldering heated up the contact to the sensor and probably melted the contact just enough to be restored. Probably it will fail again after some thermal cycling but it takes 2-3 years.
Sascha:
Can you please better explain or take a photo how you soldered EMI copper foil stripes.
Thank you in advance.
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