Author Topic: repair of Panasonic microwave inverter  (Read 549 times)

Offline Twospoons

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repair of Panasonic microwave inverter
« on: June 27, 2021, 02:31:58 AM »
Has anyone here any experience with repairing the Panasonic microwave inverters?  Mine has a blown diode bridge and IGBT, but without a schematic its a bit hard to work our what else might be dead.  No point replacing those parts if they're heading straight to silicon heaven.
My particular board is F66459X92AP.  The only reference sch I could find  must be wrong as it doesn't show a diode / zener /zener string connected to the IGBT that I can see on my board.

Would be nice to repair the microwave, rather than sending it to the trash heap.

Offline Twospoons

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Re: repair of Panasonic microwave inverter
« Reply #1 on: July 24, 2021, 03:16:27 AM »
Having replaced both the diode bridge and IGBT the microwave appears to be working again.
It bothers me that there is no obvious reason for the IGBT to blow, so we'll see how long it lasts.

Certainly cheaper than replacing the microwave!

Offline Weston

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Re: repair of Panasonic microwave inverter
« Reply #2 on: July 24, 2021, 10:08:34 AM »
Could have it failed due to an AC line surge?

Is there some surge protector on the PCB that you can check for damage? MOVs typically fail closed and will take out the fuse, but it may be an internally fused type?

Offline Mads Barnkob

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Re: repair of Panasonic microwave inverter
« Reply #3 on: July 24, 2021, 08:08:36 PM »
Are these drivers a single IGBT quasi-resonant topology like induction stoves?

A single IGBT driver for 2300W is not designed to live more than 2 years required warranty life, might even be shorter. My own experiments with the induction stoves, is that the IGBT blows up by the slightest change of load impedance at maximum power. A short overload could properly kill a MWO inverter in the same way if the magnetron can suddenly pull too much current? I am however not sure it works that way? (put more stuff in, its more loaded, or metal)
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Offline Twospoons

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Re: repair of Panasonic microwave inverter
« Reply #4 on: July 24, 2021, 10:41:38 PM »
Are these drivers a single IGBT quasi-resonant topology like induction stoves?

It would seem that way based on the schematics I've seen. The only power devices in this inverter are the one IGBT and the diode bridge.  With a single switch pushing 1kW I can't see how else it could be done - the way the transformer is built would lead to considerable leakage inductance, and the only sensible way to handle that, at that power level, would be a quasi-resonant topology.

So far everything is still running, after cooking dinner last night. And I still have a set of spares if it dies again.

And like most appliances these days I guess its designed to outlast the warranty, and not much more.  So they can sell you another one.
https://en.wikipedia.org/wiki/Phoebus_cartel <- this is why consumers get screwed over, and the world has a waste problem.

Offline johnf

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Re: repair of Panasonic microwave inverter
« Reply #5 on: July 27, 2021, 06:19:19 AM »
As magnetrons age they can have little arc overs inside especially if you present a difficult load like nothing in the oven or some sharp metal that  arcs -- resultant VSWR from this causes an internal arc / flashover in the magnetron and the silicon driving this does not like it.
So it may have died due to a power surge and slightly difficult load at the time. If it does it more regularly then you should replace the magnetron. IU have bought brand new ones from Aliexpress about US$10 each i also bought some modified watercooled variants that I have been misusing at work for microwave furnace work these were expensive ie US$50 each and I bought 10 as this was the minimum buy quantity

Offline petespaco

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Re: repair of Panasonic microwave inverter
« Reply #6 on: July 27, 2021, 04:36:37 PM »
Quote
And like most appliances these days I guess its designed to outlast the warranty, and not much more.  So they can sell you another one.
https://en.wikipedia.org/wiki/Phoebus_cartel <- this is why consumers get screwed over, and the world has a waste problem.

I just read the referenced article. It is mostly about light bulbs with filaments. At the end, the writers conclude that the mfrs were NOT trying to shorten life to sell more bulbs.
Sure, things like that are gonna fail at some point.  I was a busy boy in my teens, running around with my tube caddy, fixing TV sets with burned out tubes.

But as regards the 2 year warranty discussion-
Where I worked, the idea of the warranty was to give some support to the customer in case of early failures.  Have you folks heard of the "Bathtub Curve"?
It basically describes the higher than average early failure rate of systems as any weak components die (infant mortality).  Once past that point, the failure rates drop to some level where they tend to stay until end of life for the entire product takes over.
Vacuum tubes would be a good example of the early part of the curve.
Tape heads in a computer room tape drive would be a good example of the end of life part of the curve, since the head gap gets larger and larger as the head's surface wears away.

Offline Twospoons

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Re: repair of Panasonic microwave inverter
« Reply #7 on: July 28, 2021, 01:39:46 AM »
Oh yes I'm, aware of the bathtub curve. But the cynic in me thinks the bathtub is rather smaller than it used to be as makers of consumer goods engage in a 'race to the bottom' -trying to be the cheapest on the market in order to boost sales.
I worked for an appliance maker 25 years ago, and as I recall the design life was 10 years. I doubt that is true now, based on the dishwasher I bought recently.

Maybe inverter MWs are just more delicate - the old style with a tfr, two diodes and a fat cap seem to go forever.  But I much prefer the defrost performance from the inverter type, so I guess Ill be replacing it every 3-4 years.

Offline klugesmith

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Re: repair of Panasonic microwave inverter
« Reply #8 on: July 28, 2021, 05:15:48 PM »
Speaking of small bathtubs in kitchens, I just had to replace a LED "reflector lightbulb" over the sink.
It had become flickery for about an hour before going dark.

When LED's moved into household illumination, just like CFL's did a couple decades earlier,
they were promoted as having very long lifetimes. In the ballpark of 10 to 100 times longer than tungsten lamps.

Of course in practice, as costs are driven to minimum, end of life is generally from failure of an electronic component.
Designers are content when MTBF is somewhat longer than traditional bulbs, and not many fires are started.  It helps that most lamps go into traditional fixtures, designed to withstand the heat of 1/10 watt per lumen.
« Last Edit: July 28, 2021, 05:18:41 PM by klugesmith »

Offline imp

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Re: repair of Panasonic microwave inverter
« Reply #9 on: September 15, 2021, 02:31:24 AM »
Speaking of small bathtubs in kitchens, I just had to replace a LED "reflector lightbulb" over the sink.
It had become flickery for about an hour before going dark.

When LED's moved into household illumination, just like CFL's did a couple decades earlier,
they were promoted as having very long lifetimes. In the ballpark of 10 to 100 times longer than tungsten lamps.

Of course in practice, as costs are driven to minimum, end of life is generally from failure of an electronic component.
Designers are content when MTBF is somewhat longer than traditional bulbs, and not many fires are started. It helps that most lamps go into traditional fixtures, designed to withstand the heat of 1/10 watt per lumen.

By this, you mean the fixture or the lamp is designed to withstand 1/10 watt per lumen? Forgive my stupidity.

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Re: repair of Panasonic microwave inverter
« Reply #9 on: September 15, 2021, 02:31:24 AM »

 


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