Neff Warming drawer failures

lethbridge

Novice Member
Well, my element is shot. If your element is reading open circuit I would say it isn't worth going to the trouble of opening it up (which is pretty easy though - it is just the 3 rivets to drill out at the rear with a 4mm bit and just pull the case off which just has some thin double sided tape at the front). The wires are riveted to the element and I can't see this ever failing which would be the only thing that would be repairable. The element is very flimsy (tracks on plastic) and not repairable in my view. Where it has let go (the black mark you can see far right in middle) it has bubbled away from the glass and cracked multiple other tracks. I'm not going to waste time attempting to bypass.

IMG_1533.jpg
IMG_1534.jpg
 

lethbridge

Novice Member
I concluded it couldn't be replaced (you can see how it is riveted to the drawer as part of the assembly process and there is no sign of any spare part). Only option is a replacement drawer/bowl - but as that was £270+ delivery I opted for a complete new warming drawer - ordered N1AHA01N0B for £306 delivered (not arrived yet). I'm hoping I can just swap the bowl out to save replacing the whole thing and keeping a fully matched finish with the ovens but either way at least I have 2 years of warranty and some spares.

I noted the one from the N50 range I ordered was 400w vs the more expensive N70 range which is identical to my original at 810w. I ordered the N50 as if I can't swap the drawer front with my original it is the closest match - the stainless steel strips on the N70 are too narrow. I'm assuming the reason the N50 is only 400w is that it doesn't have a heater as well as the hot plate. But I'm now thinking that never worked in our original one as a number on here have reported - if I do retain my original chassis I may look to repair that or even swap it into the new unit.

As many have concluded the quality of these really let Neff down but I couldn't see an alternative that would vaguely match that would be any better - so it does feel a bit like throwing good money after bad. Customers who are are not competent to repair themselves would presumably be facing a c.£400 repair bill and this could occur several times in the ovens' lifetime - or you give up with this first world problem and just use it as an accessory drawer!
 

philip collins

Novice Member
Thanks for your reply. Much Appreciated.

I can understand your thoughts totally. Like you , I cannot see a viable alternative so your plan makes sense to me. I have been looking at some other manufacturers and see that they use a conventional heating element array so maybe that is another way?
I am always interested in these products so if you can find time to post any more information, it would be very interesting to me.



Good luck with your re build
Best regards
Phil Collins
 

altom2310

Novice Member
Can some one again help me. Thanks to my previous helpers Phillip and Boiler10 I have a Neff Warming drawer N21H40N3GB. Back in May /June I had the flashing light problem and found that I had an open circuit bowl This was replaced successfully and all was well until last week. Suddenly the RCD in my circuit panel tripped and on investigation found that the 13a fuse in the three pin plug had also blown. My first thought with this total short to Earth in the system was that the bowl had shortened out but on checking I have a resistance of around 180 ohms. My next thought was the heater and fan assembly. This was checked out and has approximately 95 ohms on the element. I have disassembled the control panel thinking I would see some Blow out but as can be seen the panel is clean! There are no “ smoking smells “ associated with the drawer. I really can not understand. I have reassembled it all and although No more trips of RCB there is power entering the control module but stops there! Has anyone experienced anything like this. Any help would be appreciated
 

Attachments

philip collins

Novice Member
hello Altom,
This looks like a bit of a puzzle. here are my thoughts thinking out loud:-
1. Assuming that the mains wiring is OK, the 13A fuse would have blown because of a load short or a grounding short. It seems that the load is intact because of your resistance readings but are any of the power connections shorted to earth ? I do not know this PCB but the L & N are not generally both switched and a line short inside the relay may be on your short list for examination.
2. A possible cause of the fuse failure could be the relays shorting the load to earth before the current even got to the load. Since the drawer is inactive, the relays should be investigated. can you check the relay operation and contact resistance in powered and non powered modes. Can you check to see if the 5VDC (?) power to the relay coils is being supplied by the micro processor. if so this will eliminate the processor operation and the DC power supplies on the board and point to the fault existing on the relay/power side of the PCB
3. Having said the above ,the relays, however do not normally have their metal parts earthed so it seems unlikely that this is the cause which leads me to my next comment.
4. For such a catastrophic short, I would expect that any component causing this would exhibit obvious signs of failure. I note the large capacitor on the PCB. Worth checking for a short or slight 'bulging' of the case.
5. Finally, such a big short could be caused by a live wire trapped in the chassis! Check for burns on the power wires running from the mains input to the component parts (PCB module, Fan heater - if fitted, Tray connector, Mains input socket)

You could , of course, track the short back by 'reverse-engineering' the PCB and analysing the circuit operation but this is a pain (I did it for my Neff Drawer).

Hope this helps . let us know how you get on
 

altom2310

Novice Member
Ok lots of things to do I knew it was not a simple solution to this one. I have checked and double checked what could be called the most obvious ones ie power shorting to a metal plate and no sign of anything. Your ideas and conclusions are solid. I certainly will try and do as much as possible with a digi meter when I return from a week or so away! This has given me the hump. I must get away! Ha ha. Thanks so much for this help Phillip Much appreciated. Alun
 

lethbridge

Novice Member
Well I'm still trying to source a new warming drawer to replace mine with the blown element in the drawer/bowl (see a few posts earlier). Seems there is a shortage at present (or certainly the places that sell them cheap are struggling) so decided to attempt a repair today while I waited. As expected it is very tricky to do as as soon as you get enough heat/solder to melt through the plastic to get to the tracks to bypass the failed area you end up melting the track. With a bit of persistence chasing the tracks and a meter connected across the power supply to know when I managed to strike lucky I have got it to hold. Reassembled and at present it is working - no confidence that it will hold but time will tell. It has at least also allowed me to prove that the convection heater is actually working (as I had never noticed it was even there before looking into this!), so I am thinking now I may just order a replacement bowl when it fails again - but a little undecided at present...
 

hutters

Active Member
Just wanted to say a massive thanks to those that have provided information on this thread.

We had the flashing light, tried the coupling - made no difference, bypassed the power unit and checked the heating element - worked ok, wacked the relays and hey presto it worked...for a while. Decided to order the relays from RS and give that a go - I've never unsoldered before and have pretty much zero experience with soldering, but really had nothing to lose! Components arrived today so borrowed a soldering iron and gave it a go. We now have a functioning warming drawer again (and a happy wife!). :thumbsup:
 

vlad158

Novice Member
Not any assistance but just recording another failure, really don't think these are anything like the quality they should be for £400+ - ours failed after 5 years so we were lucky, but on getting an engineer out have discovered it never worked properly - apparently setting 4 should have started an internal fan - hot air blower (it has never worked), always thought it was a bit feeble heating just via the element at the bottom of the drawer.
Well following on from the failure of the warming draw - we purchased a replacement (Neff again) and what can I say; the new versions are dreadful, no heated element at the base , replaced with a nasty rubberised /teflon matt all heating provided by the fan now. The gauge of the steel seems much thinner also, alot less stainless on show at the front which is now replaced by a black plastic front - so the oven tower now longer matched.
Asked Neff to comment on the new 'lower' quality of their premium product and did actually manage to speak to someone who said they would get back to us. (of course they never did!).
So I sent the new one back and got a full refund from AO, and put the old non-working version back.
At least the tower now matches again!
So as others here have done , I thought I'd take a chance and I purchased the control board , £106 (from Neff - grrr...) et volia , very simple , to change out, power off , draw open 2 screws, and I now have a fully working warming draw for the first time in 6 years, yes the fan works on setting 4, (it never used to even when brand new!)
The replacement PCB is radically different in design, no mechanical mechanism behind the switch, and many other components are different, so I am hoping they acknowledged the shortcomings of the old PCB (on the right) and the new version (on the left) is improved and will give improved longevity , we shall see.
 

Attachments

Last edited:

lethbridge

Novice Member
My repair to the element in the drawer/bowl didn't hold (as expected) so ordered a replacement bowl for £270 (ouch, the whole drawer cost me £306 in 2015!). Decided that was best option as it would of been a pain to change out the whole thing and the new ones are clearly no better - indeed the cheaper N50 (c.£350) that is the best match is clearly not as good as pointed out above - that explains why it's only rated at 400w vs the N70 (c.£500) which is clearly the same internals as mine at 810w.

How long the relays hold up we shall see as they have been fine to date but based on the above I think I'd plump for a new PCB rather than bothering to mod.
 

mrnmnew

Member
Just wanted to say a massive thanks to those that have provided information on this thread.

We had the flashing light, tried the coupling - made no difference, bypassed the power unit and checked the heating element - worked ok, wacked the relays and hey presto it worked...for a while. Decided to order the relays from RS and give that a go - I've never unsoldered before and have pretty much zero experience with soldering, but really had nothing to lose! Components arrived today so borrowed a soldering iron and gave it a go. We now have a functioning warming drawer again (and a happy wife!). :thumbsup:
Just wanted to say a massive thanks to those that have provided information on this thread.

We had the flashing light, tried the coupling - made no difference, bypassed the power unit and checked the heating element - worked ok, wacked the relays and hey presto it worked...for a while. Decided to order the relays from RS and give that a go - I've never unsoldered before and have pretty much zero experience with soldering, but really had nothing to lose! Components arrived today so borrowed a soldering iron and gave it a go. We now have a functioning warming drawer again (and a happy wife!). :thumbsup:
I have been following this thread and after hitting the relays the draw work for a short while so replaced the relays with 12V from RS and initially it worked. After about an hour the fault had returned with the light flashing. I have replaced the draw switch and checked the heating element. Any ideas about why it should initially work and then the fault return so quickly? I have switch the draw off at the wall and will try again tomorrow to see if that gives a clue.
 
I have had a second controller go down on our Neff warming draw which was only installed in 2017, and when looking for a second replacement found this Forum. Reading through it encouraged me to do my own investigation. The NC relay contact was found to be reading high, and so I gave it a tap with by screwdriver, but unfortunately the resistance went up from a couple of ohms to around 30 ohms. However, I also found that the 220 ohm series resistor was also open circuit and on investigation found that it had been arcing to Neutral under the body of the resistor (see attached photos).

I am in agreement with Philip Collins in that there is no protection against a large back emf being generated by the inductance of the element when the relay opens, and this is causing large voltages to be fed into the low voltage electronics. The 220 ohm resistor is rated at 1W, but under the designed operating conditions it only needs to be 0.047W. This has obviously been a problem for some time and the designers answer has been to fit a bigger and bigger resistor, without fully understanding the cause of the fault. Philip, you thought that you had damaged this resistor, but I suspect that it had already failed, especially as you have indicated on your drawings that the input voltage at the Op-Amp inputs is 2.5V, which is what I measured on mine when the resistor is open circuit and the draw is open.

The Op-Amp has a gain of 2 and its output is connected to an A-D input on the microprocessor capable of measuring up to 5V. They have done this so that they can measure the resistance of the element which is a crude form of determining the temperature of the tray. They can also detect that the draw has been closed of course (the dreaded flashing light). I had the flashing light with my open circuit resistor and as the input to the processor is almost 0V when the resistor fails and the draw is shut, they obviously flash the LED if the measured resistance is too low as well.

Like Philip, I have made a modification to try and stop this failure from reoccurring. I felt that maybe the capacitance could be lower than Philip has used and so I monitored the voltage on the feed to the draw as it is closed (see attached photo). You can see that the voltage stabilises within 0.5us and as the time constant of an inductive circuit is L/R and values get to within 1% of their final value in 5 time constants the inductance can be calculated as 0.5 / 5 * 120 = 12uH. Given that the inductance is not very large, a 10nF capacitor is adequate. I have used a resistor value of 165 ohms in order to keep the peak current to 2A when the relay closes when the mains voltage is at its peak. Unlike Philip, I have placed the RC snubber in the back of the kettle connector on the draw as I feel that in this position it protects the connector as well as the relay. In fact I wondered what voltage will be left on Philip's capacitor if the draw is opened when the mains is at its peak voltage? Any voltage left on the capacitor will be switched into the low voltage electronics when the relay opens, and could damage them.

As a parting note, I am afraid I have some bad news for vlad158, the controller you have just fitted is the same as the one that has just failed on my draw.

I hope this if use to you all, I share your pain in having purchased a poorly designed product. What I find surprising is that this is a badged product for two of the companies that supply it and so why have they not insisted that the company that makes it sorts the problem out?
 

Attachments

hutters

Active Member
After replacing the relays it has worked fine for a while, but we now have a different fault - the light flashes rapidly. Does anyone know what that indicates?
 

hutters

Active Member
Measure the large resistor with 2200 marked on the top of it. It should be 220 ohms.
My knowledge is very limited, so used an online tool to identify the resistance of each resistor on the board and none come back as 220 ohms.

Left to right on the photo below I get 1.5 kohms, 470 ohms and 47 ohms is that correct?

IMG_1297.jpg
 
You are looking at the leaded components, the little black parts with numbers on the top are Surface Mount resistors. You are looking for a Surface Mount resistor much larger than the ones in your photo with 2200 on the top.
 

hutters

Active Member
You are looking at the leaded components, the little black parts with numbers on the top are Surface Mount resistors. You are looking for a Surface Mount resistor much larger than the ones in your photo with 2200 on the top.
Thank you - found it on the other side of the board. We've resorted to ordering a new board!
 

philip collins

Novice Member
You are looking at the leaded components, the little black parts with numbers on the top are Surface Mount resistors. You are looking for a Surface Mount resistor much larger than the ones in your photo with 2200 on the top.
I have had a second controller go down on our Neff warming draw which was only installed in 2017, and when looking for a second replacement found this Forum. Reading through it encouraged me to do my own investigation. The NC relay contact was found to be reading high, and so I gave it a tap with by screwdriver, but unfortunately the resistance went up from a couple of ohms to around 30 ohms. However, I also found that the 220 ohm series resistor was also open circuit and on investigation found that it had been arcing to Neutral under the body of the resistor (see attached photos).

I am in agreement with Philip Collins in that there is no protection against a large back emf being generated by the inductance of the element when the relay opens, and this is causing large voltages to be fed into the low voltage electronics. The 220 ohm resistor is rated at 1W, but under the designed operating conditions it only needs to be 0.047W. This has obviously been a problem for some time and the designers answer has been to fit a bigger and bigger resistor, without fully understanding the cause of the fault. Philip, you thought that you had damaged this resistor, but I suspect that it had already failed, especially as you have indicated on your drawings that the input voltage at the Op-Amp inputs is 2.5V, which is what I measured on mine when the resistor is open circuit and the draw is open.

The Op-Amp has a gain of 2 and its output is connected to an A-D input on the microprocessor capable of measuring up to 5V. They have done this so that they can measure the resistance of the element which is a crude form of determining the temperature of the tray. They can also detect that the draw has been closed of course (the dreaded flashing light). I had the flashing light with my open circuit resistor and as the input to the processor is almost 0V when the resistor fails and the draw is shut, they obviously flash the LED if the measured resistance is too low as well.

Like Philip, I have made a modification to try and stop this failure from reoccurring. I felt that maybe the capacitance could be lower than Philip has used and so I monitored the voltage on the feed to the draw as it is closed (see attached photo). You can see that the voltage stabilises within 0.5us and as the time constant of an inductive circuit is L/R and values get to within 1% of their final value in 5 time constants the inductance can be calculated as 0.5 / 5 * 120 = 12uH. Given that the inductance is not very large, a 10nF capacitor is adequate. I have used a resistor value of 165 ohms in order to keep the peak current to 2A when the relay closes when the mains voltage is at its peak. Unlike Philip, I have placed the RC snubber in the back of the kettle connector on the draw as I feel that in this position it protects the connector as well as the relay. In fact I wondered what voltage will be left on Philip's capacitor if the draw is opened when the mains is at its peak voltage? Any voltage left on the capacitor will be switched into the low voltage electronics when the relay opens, and could damage them.

As a parting note, I am afraid I have some bad news for vlad158, the controller you have just fitted is the same as the one that has just failed on my draw.

I hope this if use to you all, I share your pain in having purchased a poorly designed product. What I find surprising is that this is a badged product for two of the companies that supply it and so why have they not insisted that the company that makes it sorts the problem out?
Hi GT,

The warming drawer is still working - no problems.
I chose the values of the snubber so that the ~375v peak voltage possible when the drawer opens collapses to an acceptable level and is clamped by the 220R and zener on the input of the op-amp . I used the switching time of the relay to make sure that an excessive voltage was not presented to the Op amp. (hope I got my sums right)
I think that the big 220R resistor was chosen for its peak current capability rather than its power dissipation.

looking good so far!

BR- Phil
 

The latest video from AVForums

Panasonic HZ2000 4K OLED TV Review | The best OLED for movie viewing in 2020
Top Bottom