Microwave oven loss of power

[Joe_Lorenz]

Hello,

to avoid getting into trouble by drifting slightly off topic - but nevertheless on to a very interesting subject, too - I curiously took a close look on the wiring between xformer and magnetron.

So, those are multi strand wires, crimped to the 1/4" flat connectors. The connectors themselves feel still solid and springy.

I am inclined to reinforcing the crimp areas by some solder and put some heat shrink tubing over the first inch of the wires.

Now waiting for the delivery of a NOS magnetron. At 40 Euros not too expensive, me thinks.

Joe

[kalee20]

If the crimp joints haven't given any trouble then it's probably best to not fix what isn't broke!

Good crimp connections are very reliable, and as G6Tanuki says, are widely used in the aerospace industry.

However, covering with heatshrink sleeving (if you can get it on) is a good idea, and will keep the joints and junctions clean.

[FrankB]

In the shop I worked at, I must have fixed at least 50-75 microwave ovens.
One common fault I found was the crimped connectors on the wires would lose tension, and on the Maggie fil, it would result in a low/no power condition. If the wire was loose at the crimp, I would re-crimp & use silver solder for the repair. ( Silver solder handles heat better than regular solder) if it was loose on the spade end, a good quality replacement conn would be used. Those are the first things I checked.
Yeah that capacitor can really bite you really good, so discharge it before doing anything.
Also check the maggie for leakage between elements. typically I would see a filament to another element, from lower ohms to the meg ohms. If so, it's bad. HTH

[Nickthedentist]

Useful to know, Frank. Not something I'd have guessed would give problems.

And nice to see you posting here, Frank, hope you're keeping OK considering everything.

Nick.

[Maarten]

Originally Posted by paulsherwin

I would say that fitting a replacement magnetron to a 1987 microwave oven is unlikely to make sense unless the appliance has particular sentimental significance.

It's a Swedish made Philips. If the casing is good mechanically, most repairs make sense regardless of its age. They were some of the best and later, more complex models also the most logical to operate. Whirlpool closed the factory (actually the old TV factory in Norrköping) a few years ago, and quality has severely suffered.

[Joe_Lorenz]

I'd like to agree in all aspects to this, no wonder. And there's another point not yet mentioned: These apparati (plural form of apparatus is what I mean) are cubicle-sized, not 16:9 or the like as most modern ones. That means the space inside is bigger. To find a replacement of similar dimensions seems to be impossible.

Anyway, today I received a NOS magnetron and I'm looking forward to fitting it.

Joe

[Joe_Lorenz]

Some news from the oven repair adventure:

The new magnetron 2M303 H has arrived. Looking good, all mechanical dimensions are identical, connections and cooling fins just like those of the 2M172. Fine!
So I have fitted it, the wires have got some heat shrink sleevings, and everything has been put together.
Firing it up it sounds more powerful from the first second on, but soon it has started some arcing within the cooking compartment! Accompanied to a nasty sort of noise scaring wife and cats!
So I had another look inside, found no cuprit. The mains xformer has two primary tappings for 220V and 240V. It had been set on 220V but now I've switched to 240V. A short run after that showed no more arcing, but tomorrow I will try to do the power measuring procedure as has been described above!
To be continued ...

Joe

[Sideband]

You did put a cup of water in the cavity as a load didn't you...?

[Joe_Lorenz]

Yes, I did so.

This morning my son put a sandwich in the cavity and produced nice fireworks just behind the door. Even though at reduced power on 240 V tap.

I double checked the stirrer for clean ball bearings to let it spin freely: All in good condition. Still wondering what's going on in there.

Joe

[kalee20]

I'd be inclined to get an old mobile phone, put it close to the door, set it to record video, and power-up for a few seconds. Better than putting your eye up to the trouble...

It's possible that there is a fault which killed the first magnetron. Though I can't imagine yet what it could be.

[Graham G3ZVT]

Fireworks are usually caused by the mica windows in the side of the cavity burning, however I think in this case the microwave energy is ducted via a waveguide into the top of the cavity and you might find the plastic roof liner has been burning.

[mickm3for]

Hi data shows the 2m172ah as a 850w (orignal fitted ) and the 2m303h (replacement ) as 1080w ?an extra 230w mick

[G6Tanuki]

In my experience, arcing and flashover in a microwave oven is either due to grease or carbonised crumbs in the cavity - combi grill-oven-microwaves being particularly prone to this, or if the flashing is in the door I would be checking that the perforated mesh hasn't got any obvious breaks or corrosion in it.

My Sanyo Super Showerwave combi grill/microwave/fan-oven is starting to do occasional flashovers. I have cleaned inside the cavity but it is still occasionally flashing. It's around 20 years old so if the flashing gets worse I think it is time to WEEE it in and get a new one.

[Techman]

From what Mick says in post #32, it sounds like the replacement magnetron is for a much larger microwave oven and is just too powerful. A sandwich is virtually nothing with regards to soaking up the power.

I would have thought you'd have been able to find a good magnetron from a scrap oven. I've never bought a microwave oven in my life and I've just had a count up and I seem to have got six, all old school transformer types. I think at least one, if not two were salvaged from skips. I've got three that I use in the kitchen, another two for use or for eventual spares in the garage and there's another one in an old car that I seem to be using for storage at the moment out in the back yard. All of them work with one of the ones in the garage being the first one I ever got back in the 80s. I think that one was one of the ones that possibly came out of a skip and I remember using it a lot until one day I was doing a jacket potato and left it cooking in the kitchen while I went into another room to do something else and on returning to the kitchen, found the room filled with smoke and a strong electrical burning smell. The transformer had burnt out, but all was not lost, as a mate that used to repair them found me a second hand transformer of 'similar' dimensions and on fitting it all was good once again. This oven was still working when I last tried it, probably a couple of decades ago, but it's not used now due to the turntable platter being broken/missing, although one from one of the others could probably be used or adapted to fit it.

Certainly the latest two microwaves that I've got were offered to me free when they were being thrown out, one of which is in use in the kitchen and the other is out in the storage car for want of somewhere to put it for the time being and are both fairly modern, but still simple 'transformer' types. So it's likely that I've got microwave ovens to last me a lifetime and I'm unlikely to ever have to go out and buy one. My favourite one in the kitchen is a large 'Brother, Hi-Speed+Grill' model, which I salvaged from a skip a couple of decades ago. Unfortunately, it's not getting a lot of use at the moment due to the turntable struggling and grinding to an eventual halt. I've got it mounted on a high(ish) shelf with a small TV on top of it, so it's going to be a bit of a task to get it down to service it and I'm putting the job off at the moment, but probably this summer, and take it out onto the garden table for a good service and clean up - we'll see!

[Joe_Lorenz]

Diving somewhat deeper into manufacturer's data I've found a statement at Toshiba: "It is always possible to substitute a magnetron with a more powerful type given all other data match." So, the 1050W rated 2M303 is ok to replace a tired 850W 2M172.

Further investigation got the result that this type of oven hasn't got a mica shield as the magnetron is positioned right in the middle of the "ceiling" facing downwards towards the axis of the slotted disk "stirrer". All clean and operable.

Today we noticed no more arcing and flashing, but perhaps in the door there might be some "debris" at the mesh. Got to dismantle it and give it some cleaning, too.

Performance seems to be much stronger now than before, awaiting measuring procedure now as suggested.

[Richard]

Glad to hear it's working.
It will be worth checking there is no RF leakage, meters are cheap if you haven't got one.

Richard

[Techman]

I'd be interested to know just how near to the oven you'd have to be if there was a bit of door leakage to be in any danger. I tried researching this last night and although I found lots of technical rules and regulations and figures, I couldn't find an exact answer, such as perhaps "little risk if over a metre away", or something like that. I tend to never stand looking into the oven at what's cooking for any length of time anyway.

[Red to black]

I would look at the 'inverse square law' to be honest, even with a damaged door seal on a MW oven we had in for repair once for other matters it was still within bounds of acceptable leakage requirements, we did of course replace the damaged door seal and realign the door as per manufacturers instructions, it was still within the legal bounds for leakage though even in its damaged state.

[Joe_Lorenz]

Hello again,

right now I'd like to declare that repair a success story. The oven does it's daily job as it used to do over the last decades.
No more arcing or sparking, that is gone by now after some more cleaning.
According to Richard's method I have tried to measure the dissipated power: About 680W now, that seems to be ok.
Most important: All family members are happy with it.
So thanks again to all who have contributed!

Joe

[Maarten]

Nice!

Also, the likely reason that it's possible to substitute a higher power magnetron, is that the transformer acts as a constant current source.