Replacement Safety Capacitor Help

[thomadav]

I believe the Capacitor in the image below (taken from my Neff combi-oven) is a 580nF Safety Capacitor (though I could well be wrong). I need to replace one of these that has failed, but as I'm not feeling sufficiently confident in identifying a suitable equivalent, I would be very very grateful if someone can offer a suitable replacement and a good location to buy one.

The capacitor is marked 275V-E / 584+BC / 8914.

Many thanks for any suggestions / guidance.

Thomadav

 

[Diver300]

I don't think that a suppression capacitor would have that large a value. 580 nF would give 45 mA of leakage current, which would normally be too much.

Can you work out what points that capacitor is connected between?

 

[JimB]

That capacitor is not a capacitor, it is a Transient Voltage Suppressor (275 volt)

Look here:

https://uk.farnell.com/c/circuit-protection/tvs-transient-voltage-suppressors/tvs-varistors?voltage-rating-vac=275v

JimB

 

[tronitech]

More likely to be a 275V MOV.

 

[rjenkinsgb]

It is a VDR (MOV), one of these by the look of it?

Check the diameter of the disc; if it's between 13 - 15mm this should be the exact type:

VDRS10P275BSE | Vishay, NTCLE100E3 Varistor 270pF 25A, Clamping 710V, Varistor 430V | RS

uk.rs-online.com

 

[Diver300]

It is a VDR (MOV), one of these by the look of it?

Check the diameter of the disc; if it's between 13 - 15mm this should be the exact type:

VDRS10P275BSE | Vishay, NTCLE100E3 Varistor 270pF 25A, Clamping 710V, Varistor 430V | RS

uk.rs-online.com

The "584" in the marking implies that it is a slightly different series, one of these:- https://www.vishay.com/docs/29082/vdrh.pdf

However I can't find a 275 V version for sale, and the difference between the different series is slight.

 

[rjenkinsgb]

The "584" in the marking implies that it is a slightly different series, one of these:-

OK, that's a 10mm disc rather than a 14mm disc

It looks like the size is before they are coated, so actual sizes around 12mm and 16mm.

As you say, the 584 size does not seem to be available anywhere. The one I Iinked to can withstand higher surges, so should be a suitable substitute.

 

[thomadav]

Can I just say a huge huge thank you for all your replies. I was hopeful I might get a reply in the next week,particularly when there are many more important challenges and projects to sort rather than my Neff issue, but to check messages the following morning to have a whole thread is incredible. You have all been so incredibly helpful and clearly I was way off by suggesting it was a safety capacitor. I'm going to go ahead and order the suggested substitution and we'll see if it works. Will report back and let you know.

Thanks again!

 

[Nigel Goodwin]

Can I just say a huge huge thank you for all your replies. I was hopeful I might get a reply in the next week,particularly when there are many more important challenges and projects to sort rather than my Neff issue, but to check messages the following morning to have a whole thread is incredible. You have all been so incredibly helpful and clearly I was way off by suggesting it was a safety capacitor. I'm going to go ahead and order the suggested substitution and we'll see if it works. Will report back and let you know.

Thanks again!

Why do you imagine it's faulty? - if it was faulty then it's likely to be blackened, cracked or blown apart, assuming the picture in your original post is your actual unit?, then it looks perfectly fine.

Also, even if it was faulty, you could simply remove it and the unit will work perfectly well without it - it's not a functional part. It's there simply to help protect against any possible high voltage spikes coming down the mains, for almost all of the time it does absolutely nothing - and is only really of use in countries where the mains supply is fairly poor.

 

[thomadav]

Hi, the actual unit was black, cracked and blown. The PCB has a number of these on it and I'm hoping that the spec of the blown one matches the others as due to damage it was illegible. I did actually try the microwave without the part fitted and all seemed well to start with. When I ran the microwave though, it ran for 3 seconds (programmed for 2 mins) and then just stopped. I restarted the microwave and it did the same again, so my conclusion was that it might be the blown (now removed) component that was the problem. Fingers crossed this might fix it, otherwise it's £200+ for a new PCB from Neff unless I can find one elsewhere. Might also not be anything to do with the PCB, just trying to tick off the obvious visible problems first.

 

[Nigel Goodwin]

Hi, the actual unit was black, cracked and blown. The PCB has a number of these on it and I'm hoping that the spec of the blown one matches the others as due to damage it was illegible. I did actually try the microwave without the part fitted and all seemed well to start with. When I ran the microwave though, it ran for 3 seconds (programmed for 2 mins) and then just stopped. I restarted the microwave and it did the same again, so my conclusion was that it might be the blown (now removed) component that was the problem. Fingers crossed this might fix it, otherwise it's £200+ for a new PCB from Neff unless I can find one elsewhere. Might also not be anything to do with the PCB, just trying to tick off the obvious visible problems first.

Nothing to do with that component - it should work perfectly without it. Have you assembled everything correctly?, peculiar faults (like stopping after three seconds) on microwave ovens are usually down to silly sensor faults, like you've left one unplugged, or plugged it in the wrong place, or a faulty sensor. If you've got the service manual (if there is one?) it might describe what causes stopping after 3 seconds - I'd VERY, VERY much not expect a new PCB to cure that problem.

I certainly wouldn't dream of risking £200 on something with pretty well zero chance of fixing it.

I spent 40 odd years repairing microwave ovens, though never Neff ones - but they are all very much alike, other than Philips which seem to come from an entirely different planet (if not Universe).

Very often individual parts, and even the circuit of the electronics PCB, aren't available - as most microwave engineers are just white goods engineers, and don't really have any electronics knowledge - I came from the other direction, as a TV engineer.

 

[thomadav]

Thanks for the detailed mail, I ordered the part this morning so that should arrive early this week and no hard in fitting it. I didn't disassemble the unit much, and its perhaps it's more helpful if I give you the whole story.

I bought the combi-oven second hand recently and it appeared to have a couple of faults, the oven light didn't come on and the control panel didn't seem to fit properly as it pressed in whenever you pressed a button. Oven light should be straightforward, just get a new bulb - this I did but it didn't fit though it seemed to be the right bulb. As I had to sort the front panel I took the panel of the top, back and sides (it's a built in) to get at the light. This I removed and it had a broken leg from a previous bulb stuck in it. That was easy to sort, fitting the bulb, plugged in and nothing. Tried a few things before I suspected it was the transformer for the light that was at fault. Disconnected the transformer and put a meter across it, conductivity on the output nut nothing on the input - hence I concluded it was dead. I located a new transformer and placed that on order. Then I thought, its only a 12V bulb, whilst I wait for the transformer I can run that off of another mains transformer and keep the Mrs happy. I ran a couple of leads from the new transformer and wired directly to the output of the dead transformer - stupidly I didn't disconnect anything as I'd concluded the transformer was faulty. I plugged in the new powerpack and the light came on in the oven - all seemed fine. Now I'm not sure what I did next, but I had both the oven connected to the mains and the additional power supply connected (not for long) but there was the smell of burning and smoke emerging from the oven top. (this would have been the component in question going up in smoke). Disconnected everything swiftly and stripped out the temporary additional power supply. Once the smoke had cleared, I plugged the oven back in and it seemed to be working, the oven ran and the microwave was heating water. At this point in time, I hadn't spotted the destroyed component. The next day the transformer arrived, and I carefully fitted this and it worked, the light came on but it never went off. This seemed odd, so I took another look inside and this is when I spotted the fried component. I then released the circuit board, desoldered the component - removed it and put it back together. The light now was working perfectly, only came on when the door was open. I now thought all was good until my wife tried the microwave, and this only runs for 3 seconds and then stops. I then assumed that the missing component was the reason, and that's when my thread started and hear I am now confessing to what I've done. If I'd disconnected that transformer completely I think I would have been fine, but I'm thinking that I must have 'run it backwards' which placed a high voltage into what is normally a 250V line and that fried the component. If I google 'my Neff Microwave stops after 3 seconds' two themes come up, (1) is a faulty door switch (2) are references to high voltage transformers and magnetrons which all sounds expensive and far beyond my expertise or (3) I haven't put something back correctly.

Continuity on both door switches seem to be fine so (1) is unlikely.
(2) I'm not sure I will know in this case, though I'm sure I managed to microwave a glass of water after the incident without issue which leads me to;
(3) Have I missed a connection or something or perhaps that component is significant? I'd like it to be this as I feel I know what I need to do.

Given that you've got 40 years of experience, I felt it was only right that I shared the full story with you, I've only got an 'O' level in electronics from about 40 years ago and as they say 'someone with a little knowledge can be dangerous'.

As I only recently bought the oven, then a transformer and some further parts I'm invested in trying to get this working, and also learning a lot as I go (certainly what not to do) - not sure if this will have you smiling or in despair but hope it provides some entertainment at least.

Thanks again

 

[Nigel Goodwin]

As I said, the usual issue is faulty sensors, on expensive microwaves there's often a temperature sensor and a steam sensor, and these are checked as the oven starts cooking, and if they fail that test then the oven shuts down - and this takes about three seconds. I can envision that some ovens might check the cooling fan as well?, and again would probably shutdown after about three seconds as well - but in the ones I've seen with failed cooling fans, the magnetron simply over heats until the thermal trip blows (and if you're lucky the magnetron survives).

However, as the oven hasn't just 'failed', but has been accidentally exposed to a high voltage, then it could certainly have damaged something on the PCB - the TVS is there to help reduce short transient spikes, not a continuous over voltage.

It's not much help, but you could really do with another identical oven to try the PCB from, or try your PCB in an identical oven. I used to have a big pile of scavenged microwave spares, most out of ovens where the magnetron had failed - including a goodly number of Sharp and Panasonic control boards, none of which I ever had occasion to use

There's often a crude wiring diagram stuck inside the lid of microwave ovens, does your have one?, and does it show any oven sensors, that you could check are plugged in correctly.

 

[thomadav]

Hi,

Took the time yesterday to fit the new part and check over all the connections to the circuit board, with a focus on sensors etc... as you suggested. I believe Nigel that you nailed the issue, as I checked each connection, there was one that hadn't been pushed home enough and when I looked to see where the cable was routed it ran to a sensor on the wall of the oven, so as you'd said all along more likely to be a sensor issue. Put it all back together and it's running fine as far as I can tell. I also happened to notice, the NEFF has quite a few panasonic parts in it too!

Once again a huge thank you for all your help and to everyone who took the time out and replied, I've learnt a fair bit in sorting this. Hope to use this forum again and hopefully I can help someone in return too.,

Enjoy the bank holiday

 

[Nigel Goodwin]

Well done - it makes you wonder if NEFF basically buy Microwave technology from Panasonic - it seems coincidental that it's the same three seconds for shutdown.