Microwave oven repair

[Geoff S]

Our built-in microwave oven stopped working a couple of weeks ago. I've repaired most types of electrical appliances at one time or another but never a microwave oven.   I managed to find a manual on line for our oven ( a Whirlpool we bought from IKEA about 17 years ago). It included a circuit cum wiring diagram (I prefer one or the other - preferably the former) but it was some help along with a plethora of YouTube videos.

 

Everything works, or appears to, except it doesn't do that fundamental thing - heat the contents.  The general opinion is that the most common fault is the HV circuits which generate a mains derived EHT of around 1.5kv.  The fact that it's mains derived rather than generated from a 10khz oscillator as a CRT display TV does is cause for concern and great care.  I checked both the HV diode (which has a forward volts drop of up to 9v so needs a battery as well as a normal multi-meter, which only use a small battery) that seemed OK and the HV 1mfd capacitor (non-electrolytic) also measured OK. Any way I was suspicious that the HV wasn't being generated and thought the components may be failing at high voltage so I acquired both via eBay (£15) and fitted them this morning.  I'm now getting the high voltage but still no heat.

 

The magnetron is basically a triode valve on steroids.  I know about triode valves as I used to make radio receivers with them when I was still at school so, although I'd never dealt with magnetrons  I felt to be on familiar territory.  There are only 2 connections which go to the heater (like a valve) which causes the cathode to emit electrons.  The high voltage is connected to one side of the heaters and with the help of cleverly constructed permanent magnets generates a 2.4 GHz oscillation at high power.  The usual check is to test the heater continuity (OK) then the isolation form ground - which seemed OK last week but today definitely not. So I've ordered a new magnetron (£65 delivered) and hoping our microwave will work when it's fitted.

 

Getting the magnetron out took a bit of doing. The oven seems to be built round it but with a bit of struggle I've done it.  Luckily I had a set of those funny screwdriver bits manufacturers use to try to stop amateurs like me fixing things.

 

I know it seems a lot when you can buy a microwave oven for around £100 but ours cost about £350 and has a built-in grill. It's also fitted into the kitchen cabinets and It's solidly made.  In any case, I hate chucking stuff out to landfill.  So, fingers crossed, it'll be working again soon.  I'll let you know ?

 

The internet is a wonderful place when attempting new jobs and YouTube a great resource for the technically minded.  Who needs 'influencers'?

 

Geoff

[PatMc]

Article of interest to me in the BBC website today - as I used to work repairing & maintaining "white goods" in the late '50's/early 60's then spent most of the rest of my working life in telecom equipment maintenance & repair.
I still can't bear to chuck out anything that has a chance of being repaired, often when buying a new replacement is more economical in terms of time (If that had to be paid). When buying a replacement is urgent, in SWMBO's opinion, I often repair the original & store it in the loft ready to be called into service if it's replacement fails. In fact we just bought a new electric kettle last month but I repaired the old one which now resides in the loft beside a toaster, a DVD player & hi-fi ... etc. Larger repaired items, like the old Dyson, reside in the garage.      

[Geoff S]

I think we've had similar career paths, Pat.  We have bought a cheap replacement for the microwave as a standby because we were unable to shop around and look at what's available because all the shops have been closed.  I was a bit nervous about tackling the oven but it's mostly steel rather than plastic and held together with loads of self tappers, easily removed. A lot of plastic things (like printers) are almost impossible to take apart because they clip together at unknown points with difficult to shift non-reversible barbs. I've repaired everything from dishwashers to central heating boilers but the microwave oven is a first.  I've quite enjoyed the exercise so far.

 

We bought a Dualit toaster, partly because they'e British made but mostly because they're repairable.

 

Anyway, I've had an email from the people where I've ordered the new magnetron and it should (could?) be here tomorrow. 

Edited March 3, 2021 by Geoff S

[kc]

It's a bit rich that the BBC website has that article when the BBC  programme  'Repair Shop'  which should be showing us how to repair our washing machines and toasters etc just shows people getting their teddy bears and old toys repaired free ( at licence payers expense!) !

Geoff S  do you think it's safe for us to attempt repairs to micro waves?   By 'us' I mean forum members who are skilled enough to make and repair RC planes, solder up Lipo connectors etc - that is even more skilled than the average DIY person.

[Martin Harris - Moderator]

I'm sure Geoff will know this but in case anyone is tempted to tinker, there are a couple of extreme hazards in microwave ovens - a HV capacitor which stores lethal energy for extended periods (although some have a deliberate leakage path for safety) and the ceramic insulators in the magnetron which may be made of berylium oxide which can be fatal if damaged and dust is breathed in.

 

This is in addition to the obvious danger of operating it with the casings removed when microwave leakage is more likely and lethal voltages approaching 4000v are generated..

[i12fly]

There is a new EU Directive under their Ecodesign legislation that when signed off this year will stipulate that white goods, lighting and TV's etc must be repairable and have spares easily available for up to 10 years old, and using commonly available tools. Whether UK will adopt this Directive into UK law I don't know. But anything exported to EU from UK will have to comply (is there anything?).

Now the question will be is the general public capable of safely repairing a mains powered item? Most people on this forum probably are, but for the average Joe -who isn't deemed capable of fitting a 230V plug -which is why all appliances legally have to have a plug fitted when sold. Of course the aim is to get a professional repair engineer out to fix the problem or take it to a Repair Shop, but as we know the cost of doing that is often more expensive that buying a new one. However the EU believe that the Directive will save the average household 150 Euro per year and lots of carbon emissions.

[Gary Manuel]

On the subject of microwave ovens, my Grandmother bought the wife and I one of those new-fangled microwave machines when we bought our first house in the early 1980's. She paid a king's ransom for it as it was a top of the range Panasonic Genius NE691. It's still going strong after 40 years of heavy use. We have another built in Smeg microwave that sits alongside our Smeg oven since I installed the new kitchen 5 years ago. It's never been used because we prefer to use the old Genius which sits on the worktop above it. We have developed a sentimental attachment to it!

Anyway, I was surprised to see this article in the Daily Mail when I was looking for info on the microwaves release date. Could it be the oldest working microwave in the country? Not sure whether Fred still has his Genius, but ours is still going strong.

 

https://www.dailymail.co.uk/news/article-1126982/Britains-oldest-microwave-going-strong-40-years--150-000-meals.html

 

Edited March 3, 2021 by Gary Manuel

[Don Fry]

A case of who benefits or pays. This tale is from SW France, but just before the rupture from the lost country.

 

I bought a cheap analogue microwave oven from Lidl. I've grown tired of expensive failures. These things seem to be reasonably reliable, or at least cheap. I suspect I am hard on these things.

 

It came with a 2 or 3 year warranty. It went wrong. This thing cost £50.

 

Lidl said, return it, at their cost, to Germany. ( that said, post costs within mainland Europe are reasonable, but considerable for heavy things like these, courier both ways).

 

After a while, a new microwave oven arrived. 
 

For a £50 unit?

Edited March 3, 2021 by Don Fry
Tidy the English.

[PatMc]

1 hour ago, kc said:

It's a bit rich that the BBC website has that article when the BBC  programme  'Repair Shop'  which should be showing us how to repair our washing machines and toasters etc just shows people getting their teddy bears and old toys repaired free ( at licence payers expense!) !

Geoff S  do you think it's safe for us to attempt repairs to micro waves?   By 'us' I mean forum members who are skilled enough to make and repair RC planes, solder up Lipo connectors etc - that is even more skilled than the average DIY person.

The Repair Shop is a very popular entertainments programme & probably low cost compared with much of it's "celebrity" rich competitors. Does a good job as far as most people (licence payers) seem to be concerned.

[PatMc]

52 minutes ago, i12fly said:

There is a new EU Directive under their Ecodesign legislation that when signed off this year will stipulate that white goods, lighting and TV's etc must be repairable and have spares easily available for up to 10 years old, and using commonly available tools. Whether UK will adopt this Directive into UK law I don't know. But anything exported to EU from UK will have to comply (is there anything?).

Now the question will be is the general public capable of safely repairing a mains powered item? Most people on this forum probably are, but for the average Joe -who isn't deemed capable of fitting a 230V plug -which is why all appliances legally have to have a plug fitted when sold. Of course the aim is to get a professional repair engineer out to fix the problem or take it to a Repair Shop, but as we know the cost of doing that is often more expensive that buying a new one. However the EU believe that the Directive will save the average household 150 Euro per year and lots of carbon emissions.

I think most of the points you make are covered in this link I posted earlier.

[Gary Manuel]

2 minutes ago, PatMc said:

The Repair Shop is a very popular entertainments programme & probably low cost compared with much of it's "celebrity" rich competitors. Does a good job as far as most people (licence payers) seem to be concerned.

I agree. The Repair Shop isn't about showing how things are repaired. It's about the emotional attachment that people have with their treasured items and how the team go about extending / restoring the life of those items. The joy on the faces of the people when they see their old stuff restored is what it's all about.

[kc]

I think the same joy would appear on anyones face if the Repair Shop repaired their washing machine or toaster for free!  

[Geoff S]

Certainly you have to be careful of the HV when the oven is connected to the mains.  In my early life I had a job testing faulty line output transformers returned to the factory.  The LOPT s also generate the EHT (extra high tension) for the cathode ray tube anode which at that time (1950s) was around 7kv.  We were supplied with open TV chassis with a row of croc clips mounted on a strip of Perspex to which we connected the wires from the LOPT (they were oil-filled and had a thermionic diode rectifier inside which could be replaced at the factory and re-cycled as spares).  I think modern H&S would have a nightmare.  I used to get at least one 7kv shock/day but they were very low energy and, as is said, 'it's the volts that jolts but the mils that kills'  and so survived. Hence, I'm fairly well used to working with high voltage kit.  We were always taught that when working with a live TV to keep one hand in your pocket.  In the case of the micro-wave oven it's just a matter of shorting out the HV capacitor once the mains is disconnected.

 

The thing I'm most careful with is microwave leakage but, so far, that hasn't been a problem as it's not been working.  Like everything else we do - just think and be careful.

 

I've been fitting mains plugs since I was a schoolboy.  When I went to a customer with Dad he would often give me the job of fitting a new plug.  We did once get a call from a customer that after he'd put a plug on an electric fire the main fuse had blown.  I went out and had a look at his plug.  All the wires had been correctly connected to the appropriate pin but he'd stripped the insulation so far back it was bare outside the shell and fused together like a copper bar!  Never seen anything like it before or, thankfully, since.

 

@i12fly  I'm not sure how capable the general public is.  The guy above was an amusing rarity who got away with trivial fuse repair.  I've been messing about with electricity all my life and most people I've known tend to practical types (including my wife) though I'm occasionally take aback by someone's ignorance.  But then, everyone is ignorant about most things, I suppose.  eg Black holes are unimaginable to me ?

 

@kc I agree about Repair Shop.  It's become a bit too emotional for me and not so technical.  Practical repair advice would be helpful but perhaps there are liability issues.

 

Geoff

 

PS I wrote this yesterday but lost it by moving away for a reference and couldn't be bothered to retype it.  It's just reappeared.  That's a great feature of the new forum. If only I knew how to make it happen ?

 

[Geoff S]

My new magnetron arrived this afternoon about 4.30.  It's now fitted, tested OK, and the Microwave oven is back in place ready to last another 17 years which is, in all likelihood, longer than we need ?.

 

Not sure if it's cost-effective but at least it's saved from land fill.  I suppose getting done professionally would be quite expensive.  I spent quite a lot of time working out how to do the job which a pro wouldn't need.

 

Geoff

 

 

[Gary Manuel]

You're a braver man than I Gunga Din.

 

Nothing to do with cost-effectiveness. You set yourself a challenge and you rose to it. ?

[Dwain Dibley.]

Well done Geoff.

D.D.

[Geoff S]

Thanks, gents.  My wife enjoyed her microwave cooked porridge this morning so I'm in good books there, too (I'm a muesli and black, unsweetened coffee man first thing)

 

Actually I quite enjoyed the challenge but the big plus on these jobs are the resources offered on the internet - YouTube etc for education and instruction and search engines to locate the parts.  How did we manage before?  In my case I usually asked my dad but, sadly, he's no longer available and, being retired I don't have work colleagues to quiz either.

 

Geoff

[Alex Ferguson 2]

A interesting story and a happy ending so should be suitable for the Repair Shop... maybe?

 

The last microwave oven I repaired required a small hacksaw, a chisel and a knife. These were used to shape a piece of wood. Oh!!! and you thought we were talking electronics? The wood was fastened into the microwave to stop the door catch bracket from bending back and the catches not fastening and therefore not allowing it to switch on. Simply poor construction by the manufacturer.

 

So my background to this hi-tech repair? Called in a couple of times to fix things for NASA, and a life time of doing repairs and designing things for a University Chemistry Department. DC to daylight? No we went way above that DC to xrays at least.

 

The most recent "domestic" repair? Our Men's Shed fridge kept blowing the RCD (circuit breaker/fuse) and it came down to electrical leakage to earth in the icebox heater. Basically a "chuck-it" though someone might use it as a beer fridge with the faulty item removed. The replacement fridge was $50 (25 pound?) second-hand from someone just up the road. It makes a change from installing operating systems (Linux) in older laptops (mainly) to keep them useful. Oh, and there is a vintage clock on the bench to rewire too. A semi-transparent drum revolves with a picture on it and the light bulb needed replacing and the wiring tidied up.

Edited March 9, 2021 by Alex Ferguson 2

[Phil McCavity]

On 04/03/2021 at 21:16, Geoff S said:

My new magnetron arrived this afternoon about 4.30.  It's now fitted, tested OK, and the Microwave oven is back in place ready to last another 17 years which is, in all likelihood, longer than we need ?.

 

Not sure if it's cost-effective but at least it's saved from land fill.  I suppose getting done professionally would be quite expensive.  I spent quite a lot of time working out how to do the job which a pro wouldn't need.

 

Geoff

 

 

Good news Geoff and a huge feeling of satisfaction on many levels.

We all need to start moving away from that 'cost effective' mentality and think longer term like you have. Things have changed, it was good while it was sustainable.....it's not anymore.

Edited March 9, 2021 by Phil McCavity

[MattyB]

On 04/03/2021 at 21:16, Geoff S said:

My new magnetron arrived this afternoon about 4.30.  It's now fitted, tested OK, and the Microwave oven is back in place ready to last another 17 years which is, in all likelihood, longer than we need ?.

 

Not sure if it's cost-effective but at least it's saved from land fill.  I suppose getting done professionally would be quite expensive.  I spent quite a lot of time working out how to do the job which a pro wouldn't need.

 

Geoff

 

Well done. I suspect a pro would need at least as much time to work out what to do though, as no-one normally wants to even try repairing something like a microwave, and that's if you can find anyone to do it in the first place!

[Phil McCavity]

On 04/03/2021 at 15:30, Geoff S said:

PS I wrote this yesterday but lost it by moving away for a reference and couldn't be bothered to retype it.  It's just reappeared.  That's a great feature of the new forum. If only I knew how to make it happen ?

 

I's easy Geoff, you just reopen the reply box.  

Unless you actually post it or delete the reply you started typing just sits in the dialogue box ready for you to do one or other. It'll remain there indefinitely until you do.