Neff B47CR32N0B/30 built in electric oven. Need assistance identifying precise fault

[SteS]

Hello.

Thank you in advance to anyone who can provide some assistance with this.

I was asked to take a look at my in-laws oven, a NEFF B47CR32N0B built in oven. The symptom is as follows:

Switching on the appliance, and any grill based operations work just fine, however if you run anything that starts the main oven going, it cuts off stone dead like you’ve pulled the power, all panel lights go out for two or three seconds, until it powers back up into its factory state, prompting you to set the time.

My initial thought was this was the element having gone short, but having taken the back panel off and measured the resistance across the element, it seems to be a reasonable level (about 25 ohms) which matches up to the power level that element is supposed to run at according to spares lists I’ve looked at for that oven.

The only other common element to when the failures were occurring was the fan itself. So I found the plug which went to the fan, unplugged it, went through the same process to start the oven cycle, and sure enough, the oven now started firing up, and the element started heating.

The question I have is this – is this the fan as first impressions might indicate, or could it still be the mainboard? The board makes a very light steady ticking noise when powered up, which strikes me as odd.

It’s just both these parts, from Neff, are north of £100. This is a grands worth of appliance, so that’s not the end of the world in the grand scheme of things, but I’d still rather be fairly convinced which item I’m going for so I don’t waste money if I can at all help it.

Does anyone know any way I can narrow this down a little more certainly?

Thanks very much.

Here is a picture of the items in question, the back of fan assembly and the mainboard, with the offending cable, which goes to the fan, unplugged. The board isn’t sat in its mounting properly in that picture as I was gaining access to the rear of it to try and trace some connections.

[electrofix]

my first thought is power to the oven

have you checked the power to the oven when it fails. what i mean is the fault in the house wiring not the oven

Dave

[SteS]

Dave,

Thanks for the response.

Honestly, I doubt it’s the power to the oven. This oven is paired with another similar single oven with microwave functionality, and behind them, both of their power cables are wired into a junction box, which then goes to the cooker isolator up on the wall. The other oven has no problem at all, and the wiring is all solid – I had to disconnect the oven that’s having problems from the junction box directly, as the cable isn’t long enough to pull it out the cabinet otherwise. I double checked all the wiring before I started that, and it was all in tight and secure.

Particularly considering I can get the elements to fire up, in the grill and the main oven compartment, they’re a few kilowatts a pop, whereas the fan can’t be more than about 10 watts, I wouldn’t have thought.

Nothing’s jumping out to say the supply has anything wrong with it, honestly.

Thanks again.

Steve

[electrofix]

no probs is always the place to start

you say you disconnect the fan and it runs have you tried the long shot of disconnecting element

as for the fan there is no way of testing it off the board so if its the fan causing it then its a swop it and see

did you try other oven settings that use the fan and does it fail on these too ?

Dave

[SteS]

Dave,

I haven’t explicitly tried running without the element, but I will add one thing I didn’t mention in my original response, for fear of muddying the waters. The element was my first suspect, and without having had the thing apart at all, considering the element was £30 and it’s the thing that often goes in electric ovens, I ordered one first, and the one that’s in it now is actually the new element – and it didn’t change the behaviour at all.

Granted that doesn’t demonstrate if the board is happy with no element but a fan connected. It could be something to try for sure.

I tried several settings, and I think yeah, anything that powered the rear fan up killed it. The top fan, however, ran just fine.

I’d like to try the fan directly but I’m just not sure what sort of connection it requires. It has four pins, red black yellow and blue, and it’s tempting to assume that red and black are power, as there’s a prominent marking on the back of the fan’s driver board that says “24V DC 4.8W”, and that the yellow and blue wires are possibly a OPR pulse telling the rest of the system that the fan is rotating, but that is, I will stress, a complete guess. The motor seems to be fairly clearly of the DC brushless variety, so it has a lot of complexity on the driver board. I’m assuming as I say the 24V just goes in on the red and black, but I don’t know if it needs to see a resistance or a short or whatever else on the other two wires in order to fire up, or if it’s just a report back on the RPM, or some other status. Or, indeed, whether it’ll just fire up with those two pins left disconnected.

In other words, at the moment I don’t know enough about that motor to know if, if it were to stay stubbornly stationary on applying power, that’s because the motor is dead, or because I’m just not giving it the right signals to get it to kick in.

Thanks
Steve

[electrofix]

you cant run the motor without the board

Dave

[SteS]

Dave,

I suspect, with it being a 4 wire DC brushless with a driver board that two wires are power and two wires are for some sort of PWM signal to control the speed. Sometimes with no signal on those, the fan will run at full speed, but without knowing before you start it’s pointless going that route.

Would you have any other recommendations on how to move forward with diagnosing? It’s clearly something to do with the fan but I really don’t want to drop £100 on one and find it’s still doing the same when I swap it, because it’s in fact the main board that’s gone.

Thanks.
Steve.

[electrofix]

thats the problem. they introduce complexity and fault finding get a lot harder

Dave

[SteveIT]

Hiya Steve, just seen your message about the fault you had with the Neff oven, my parents have exactly the same oven, and sounds like exactly the same fault as the one you have, grill works fine, but turning oven on causes the oven to turn off. What did you do in the end to get it working ? Thanks for any suggestions. Steve

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