DIY Microwave Repair

[Citroënbender]

Quick one:

Is it safe to discharge the high voltage cap by shorting across the terminals with an insulated screwdriver?

[five 7]

[Citroënbender]

All good, I decided it was safe to earth each pin to chassis first, then bridge them, repeating several times. Hopefully just the diodes which are finished.

[Tonz]

wheres the video?

[JasonACT]

Originally Posted by Tonz

wheres the video?

I'd settle for just the audio.

[aussiblue]

Many have a special discharging point if you can download the service manual. The attached picture is from the service manual of my Panasonic NN-CD997S Microwave Convection Oven.

[aussiblue]

I usually use a high wattage incandescent light I have rigged up for this purpose when there is no dedicated discharge point. This way i can watch the glow of the bulb fade away and be fairly sure it is fully discharged. Like this https://www.youtube.com/watch?v=HmbwM8cM1FU

[JasonACT]

Yeah, that's my preference too, but I notice the DC current does make the glass globe turn black on the inside fairly quickly.

[Citroënbender]

I read up, it’s a 1,14uf cap and quite possibly has an internal resistance for discharging over time. Old microwave; 1992-ish.

Yet to test the diodes, but their fly leads are quite black (no cooked electronic smell though).

There was a brutal trick in electronic repairs of charging a large electrolytic cap and then tossing it to an unsuspecting victim “Catch!”… Has probably gone the way of setting fire to apprentices.

[Citroënbender]

I tried a basic Vf measurement of the diodes, using multimeter and 9V battery. Instead of almost nothing (being rated at 9V forward) I got 3-6V depending on direction. So I’d say they are flaky.

[XD 351 Ute]

Originally Posted by Citroënbender

I read up, it’s a 1,14uf cap and quite possibly has an internal resistance for discharging over time. Old microwave; 1992-ish.

Yet to test the diodes, but their fly leads are quite black (no cooked electronic smell though).

There was a brutal trick in electronic repairs of charging a large electrolytic cap and then tossing it to an unsuspecting victim “Catch!”… Has probably gone the way of setting fire to apprentices.

Having just come across this thread, and me being a fitter, I was going to suggest get the apprentice to do it, but you beat me!

One of my cousins is an autosparky, and years ago they had an apprentice nickinamed "Osram" for various reasons....

But back on topic, I am unable to offer a solution to your problem..

Ed

[zilo]

Originally Posted by Citroënbender

I tried a basic Vf measurement of the diodes, using multimeter and 9V battery. Instead of almost nothing (being rated at 9V forward) I got 3-6V depending on direction. So I’d say they are flaky.

If they are schottky diodes that test is meaningless.

What number is on the diodes?

As for discharging the caps the best technique is a 1 megaohm resistor acrross the terminals.

Time to discharge is 5 times capacitance x ohms (farads, ohms)

[Citroënbender]

I don’t believe they are Schottky diodes.

[ESPJG32]

Hi Citroen Bender,

Well your very first comment at the start of the thread is how we used to do it when I was in the trade

[Citroënbender]

We used to do that with the 450V electrolytics in valve amplifiers, short to ground several times. I knew microwave ovens had higher voltages so wasn’t sure if it still was a viable (safe) approach.

[Citroënbender]

Change of diodes, no change in symptoms. :-/

[aussiblue]

Change of diodes, no change in symptoms. :-/

So what are the symptoms?

[Citroënbender]

No heating at all. Lights, fan, platter all work fine. Transformers don’t smell burned.

[Itsme]

Originally Posted by Citroënbender

No heating at all. Lights, fan, platter all work fine. Transformers don’t smell burned.

In this day and age who repairs appliances, and TV's

Your fault is most likely either transformer or magnetron possibly burnout or open circuit which would not be cheap to replace.

[marty351]

Food for thought...

When to Replace Your Microwave
Of course, not all microwave malfunctions were meant to be fixed. The low cost of a new microwave combined with the potentially stacking cost of replacement parts and repairs can often make it more practical to just buy a new one. The microwave is the only necessary home appliance that follows this rule, but it’s important to know when you can save time and money by making the right move.

Microwave is Over 6 Years Old
The first indicator that your microwave is better off replaced is the five-year lifespan. Microwaves can last a long time, but they have the shortest lifespan of household appliances. If your microwave is over 6 years and especially if it’s approaching 10 years old, you’re likely better off with a new microwave. Upgrade your features and don’t worry about keeping a dinosaur running.

Multiple Stacking Problems
Another indication that you should replace your microwave instead of replacing a part is if you have more than one problem to tackle. The more issues stack up. the more repairing there is to do. The cost of replacement parts will also begin to stack along with the hours necessary to fully repair your microwave. In addition, stacking technical problems usually indicates that there are more problems to come. Systematic failure is the symptom of an old, badly damaged, or very poorly designed microwave.

The Magnetron is Damaged or Burned
Finally, there’s the magnetron. No matter how new your microwave or if there’s only one problem, if the magnetron is out then you might as well replace the entire appliance. The magnetron is the heart of a microwave that actually makes the micro-waves. Replacing it is about equal to the cost of buying a whole new microwave, sometimes even greater. If the magnetron is busted, microwave replacement is a part of your future.

[JasonACT]

I bought my Sharp Carousel in 1995, I use it once or twice a day for 12 to 20 (but sometimes 45) minutes (convection and/or microwave, depending on what I'm having). I had to solder wires in where the ribbon cable connects the buttons to the micro-controller about 14 years ago, to get all the buttons working after being eaten by cockroaches in QLD while I lived there.

But they don't build them like this anymore. It was the most expensive bastard I could buy when I got my first job out of Uni though. I'll give it a crack, if something else goes wrong again, anytime soon.

Incidentally, I opened a mates once, it was rusted out and was no doubt unsafe, a much newer one than mine though.

[aussiblue]

Some are very fussy about mains voltage; if your mains voltage is not up to the spec specified for the inverter they may not cook. I have this issue where my microwave has a 250V rated transformer. This used to be fine in WA where the voltage was always 240V plus and often 250V or more but in recent years with the the impact of people using solar panels (well that's Synergy's excuse) the mains voltage is now often only 230V or less and the microwave would not work at those voltages. There is a replacement 240V inverter usually fitted to eastern states models on order and if it ever arrives (and Australia Post haven't lost it) I am told it will fix it.

[JasonACT]

When I was a teenager (oh, if only I could go back) I was mates with a tech retiree who lived over the road from my grandparents... He said his microwave took forever to cook at certain times of the day, and when he measured the voltage, it was always low when it didn't work (Manly, Sydney, where I spent a lot of school holidays).

[Citroënbender]

Magnetron is $60 and 10km away, that will put me in for $73.50 so far if it works. Versus new microwave and modifying cabinet fascia to suit.

[Itsme]

Originally Posted by Citroënbender

Magnetron is $60 and 10km away, that will put me in for $73.50 so far if it works. Versus new microwave and modifying cabinet fascia to suit.

Not only to save money and wastage but I gather you like tinkering and in for the challenge ;am I'm correct in stating this?

[Citroënbender]

It’s ingrained, to be resourceful. Plus I have a bit of near-forced downtime while I pander to the whims of others, and jobs that can be progressed in 20-minute bites are no problem.

[aussiblue]

From the same era I think CB. I just spent the day fixing the screen on a mobile phone and diagnosing why the better half's Lenonva pad won't turn on. It is getting harder though as the parts get smaller and harder to source and my eyes get weaker (thank god for microscopes head band magnifiers) and my arthritic sausage fingers get clumsier.

[Itsme]

Originally Posted by Citroënbender

It’s ingrained, to be resourceful. Plus I have a bit of near-forced downtime while I pander to the whims of others, and jobs that can be progressed in 20-minute bites are no problem.

I was the same once but these days cannot be bothered with the cheap plastic junk they manufacture.
I will only touch vintage electrical gear that is worth preserving.

Cheers and best of luck with your microwave oven.

[whitelion65]

Good on you CB!
We have a toaster (4 slice, 2 channel). A few years ago, an element blew, and knocked out one channel. This year, another blew, rendering the thing a paper-weight.
I can get the elements, but to fix one side is more expensive than the new model of the toaster.
My wife thinks I have thrown it away, but I cannot bear to do.
Will pull it down when I have some down time, for if nothing else, to salvage the usable elements.

[Citroënbender]

And fixed.

Bâtards at the parts place jagged me $30 over list price for the magnetron; good way to kill repeat trade.

So $98.50, a bit of driving, a dab of soldering to change 1/4” spade terminals to 3/16” (augmenting the crimps) and it’s all done.

Now to the naughty Italian out front.

A footnote on resourcefulness:

When I was young, WW2 was modern history. So much as one had tales of release from Egypt at Passover, stories of wartime survival against the odds were real and contemporary. One that’s carried with me was a family en route to the camps, changing trains before the last stop. An old man was doing sweeping/tidying; hunched over - he knew - although others didn’t yet. As he passed teenage boys - too young to go with their fathers, he’d mutter under his breath “You’re sixteen and you’ve got a trade”. He’d pass them on the way back and mutter it again.

There was another review of the passengers, looking for people who might be considered suitable for work rather than just a quick end. One boy, somehow grasping the significance of this division, when asked his age volunteered “sixteen” - and when asked if he was still at school: “I’m a carpenter”. So he was led away to join a work gang - the others pretty quickly worked out he knew almost nothing but covered for him, kept him working and learning enough on the job to survive. How this fellow precisely ended up in the North Country, I don’t know - but it resulted in him knowing well, friends of my parents, and how the story lives with me. And why I have a trade.