Repair of Bosch induction cooktop touch controls

[cozza]

At home our Bosch induction cooktop became unresponsive to the power on button, in the last week of it's two year warranty. Fortunately I was able to arrange to be there when the repairman came, and replacement of the display / touch panel solved the immediate problem.

It's not an uncommon fault for one or more of the buttons to stop working or be intermittent in operation, according to the repair person. I asked if I could keep the old board to have a look at it, which was fine, because "no one can fix those mate!"   

The board is fairly involved and has touch pads, the led displays, a control microcontroller and a sounder. It is made by EGO, and apparently is common to a whole swathe of other European brands, including Gaggenau, Neff, and possibly Smeg as well.

Inspection revealed that the touch pads connect via a resistor into the inputs of HC4053 chips, a triple 2 channel analog multiplexer. There is no external protection for ESD for the conductive pads which sit below the glass cook surface, although the HC4053 has protection internally.

Replacement of the 74HC4053 associated with the power switch restored functionality, so now we have a service spare board should the fault arise again. I also replaced the HC4053 IC associated with element selection, as this had been unreliable for most of the life of the appliance, although not annoying enough to warrant a service callout.

Hopefully this will be of help to other EE's in an out of warranty predicament.

[chris_leyson]

It's not an uncommon fault, for one or more of the buttons to stop working or be intermittent in operation, according to the repair person.

not at all surprised because it's designed by engineers who don't give a damn. Well maybe the engineers do give a damn but they have to design to minimum manufacturing cost and not for performance and long term reliability...

[cozza]

I'm dreading the day I have to pull out the Bosch wall oven to investigate the similarly (mostly) unresponsive touch controls on that..

It's now out of warranty.

[cozza]

As a non warranty replacement of this control board will set you back over $700 NZD, it's compelling to change the $0.88 NZD chip instead.

Farnell / Element14 2445306

[james_s]

Maybe contact some service shops and offer to purchase defective boards. If new ones are that expensive you can sell refurbished boards on ebay for a tidy profit.

[Pasa001]

Thank you Soo much for posting this. I purchased a Bosch induction cooktop from Europe and brought it back to my home in Hong Kong. The cooktop work fine for two years and now is exhibiting the same unresponsive touch control on/off function (very intermittent). I contacted Bosch repair in Hong Kong but seeing that I imported the appliance they will not service it. I noticed you posted some pictures of the touch control panel, may I ask a huge favor? Could I ask if you would be Soo kind as to take a close-up of the components your replaced? While I'm not an electrical engineer I'm pretty good with a soldering iron and I'd like to attempt the same repair. Thank you so much. Conversely if you offer a repair service I would be happy to post you the touch panel for the repair.

[cozza]

Hi Pasa001,

Assuming you have the same board with the same fault, here's what I would do :

If you look at the 4th image of the board, the HC4053 component replaced is the small black square with 16 pins (8 per side). From the part number and link in the thread you can look up the part (it is a TSSOP package on my board) and either source from farnell / element 14 or locally. Look at it with a magnifying glass - it will have 4053 written on the part if it is the same.

The power touch pad HC4053 chip is the one located close to the power on / off sensor pad, you will be able to see a circuit board connection from the touchpad to a SMD resistor, then onto one of the pins on the chip. Once you've confirmed which chip is controlled by that power pad, you could get an electronic service company to replace it for you, one with experience in phone laptop board repair would have the necessary skills - it is not an easy solder job.

Due to all the surrounding plastic parts which are heat staked through the pcb, (and the board is double sided, both sides have components on)  hot air rework is not the best option. I used flux and a soldering iron to bridge 8 pins on one side of the chip, then heated them all up together while lifting one side of the package off the board very slightly with tweezers, then alternated heating side to side to get the chip off (you have to be very careful not to tear the pads off the board)

Then when the chip is off, clean the board with desoldering braid then isopropyl alcohol before soldering the replacement chip. Note the chip orientation (it must go back the same way around) before you remove it with a photo. I used the tip, flux and drag solder technique.

If you take the board in for repair, put it in an anti static bag or wrap it in tinfoil (in a pinch) for transport.

I'm not able to offer a repair service personally for this type of repair, sorry, but I hope this helps.

[cozza]

On my board, the chip is located directly underneath the on / off button, which is the gray square with no symbol on it.

[cozza]

@ James_s , thanks, but I'm not interested in taking on the liability.

These induction cooktops can be wired in either one two, or three phase configurations, there's no way that anybody inexperienced should be taking the top glass off unless they are suitably qualified to do so safely.

The supply must be turned off at the switchboard.

[Pasa001]

Thank you Cozza! , I'm very careful  and I'll definitely switch the corresponding breaker off, I've yet to remove the circuit board , with all the things going on with the Corrona virus I plan to return home to Canada for a month and possibly try to source the components I need there. I'll post updates when I proceed with the repair in the hopes it helps others. From what I've read many of these Bosch cooktops have the same problem.

[Pasa001]

Well thanks to Cozza I've ordered the correct components and I've now disassembled the cooktop and removed the touch circuit board. Wow I didn't realize how tiny the components are so I'm afraid I'll have to find a competent repair facility to carry out the repair. It's definitely beyond my soldering ability! I'll source a new board for the time being and get this one repaired for the future. I'm really disappointed at Bosch , with the amount I spent on this cooktop it should last more than 3 years, I'll post again once I get the board repaired and update anyone that might be interested. Thank you so much Cozza you are a champ and I'd be lost without your help.

[Pasa001]

Picture of the board

[Pasa001]

Sorry I'm new at posting

[Pasa001]

Last one

[rvalente]

Thats why I use a gas stove, not much to break other than a igniter coil.

[cozza]

That looks to be the same series of board, from a larger cooktop. I'd try getting it fixed before ordering a new one though.. there must be a good surface mount rework place somewhere nearby in Hong Kong?

As the metal strips on the end of the cook surface are grounded, I've gotten into the habit of touching the trim before touching the controls to dissipate any body charge to avoid a repeat failure 

If I was in your city I'd take you up on that beer,  after changing the chips!

[Pasa001]

Repairs have been completed. I took the board to a cellular phone repair facility in Vancouver British Columbia and explained to them what I needed repaired. They unsoldered and resoldered two  HC4053 chips on the board completed the work for 100.00 Canadian dollars. I'm not returning back to Hong Kong until mid April so I won't know until then if the repair was successful. I'll post again once I reinstalled the board into the induction cooktop. I added a picture of the two chips that were replaced. 

[Pasa001]

Last one

[thm_w]

It's not an uncommon fault, for one or more of the buttons to stop working or be intermittent in operation, according to the repair person.

not at all surprised because it's designed by engineers who don't give a damn. Well maybe the engineers do give a damn but they have to design to minimum manufacturing cost and not for performance and long term reliability...

I agree with the second point, very few people care about long term reliability. But your first point is a bit off base.
This is a four layer board, its not "no expense spared" but its very clearly not the cheapest design that could be made. Look in an average microwave oven and you'll see a single layer board with no-name components.

[ClausRye]

I found this article very interesting even though it is a little bit old.

I have the same board not being able to turn on the power.

After removing the glass top-lid I found the power touch-sensor still working (touching it directly) making it possible to turn on the device and test-operate the the other touch-sensors directly without the top-lid.
With the device turned on, I have tried to mount the lid hoping to test/operate the cooktop. Unfortunately I am too slow as it turns off automatically after 10-15 secs...  So I can not tell if the other sensors are working with lid on.

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?

[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.