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Old 3rd May 2018, 10:18 pm   #21
Refugee
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Default Re: 1980s Pansonic microwave - repairable?

You will need a resistor and power supply.
They are a stack of diodes in a single package.
Perhaps 10 volts forward.
Connect it in series with a 1K resistor and measure the voltage across the resistor while increasing the power supply voltage or just replace it at the same time as the fuse.
The diode will not cost any more than a new fuse of that type.
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Old 4th May 2018, 5:44 pm   #22
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Default Re: 1980s Pansonic microwave - repairable?

Quote:
Originally Posted by Colourstar View Post
Before I replace the blown 500ma fuse, Im wondering about the condition of the diode in series with it. Presumably a short in that would cause the fuse to pop, although I can't get any reading either way from the diode on a meter....
Looks to me like the fuse and diode are intended by the manufacturer to be treated as a single assembly [that crimp between them suggests the diode and fuse wouldn't be available separately]

Replace both, and be sure the job's a good'un.
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Old 4th May 2018, 6:54 pm   #23
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Default Re: 1980s Pansonic microwave - repairable?

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Originally Posted by G6Tanuki View Post
Replace both, and be sure the job's a good'un.
Indeed! And it seems the fuse may be a special high voltage type too.

(And thanks to Refugee for the test procedure by the way)

EDIT: I've found a spares company in Australia that stock the complete Panasonic fuse + diode assembly, so I'll see if they ship to the UK.

Steve

Last edited by Colourstar; 4th May 2018 at 7:21 pm.
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Old 4th May 2018, 8:00 pm   #24
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Default Re: 1980s Pansonic microwave - repairable?

Many designs leave out the HV fuse completely, on the basis that the transformer is run close to saturation.

The safety aspect regarding electrocution cannot be overstated, but beyond that, they are arguably amongst the simplest of white goods to repair, having only a handful of components in the actual microwave generator:
Transformer, rectifier, capacitor, magnetron, and the classical 3 microswitch door interlock which is capable of crowbarring the mains fuse in the last resort.

I repaired hundreds of microwave ovens for an insurance company about 15 years ago.
The oddest one was the Breville I had to write off because I couldn't source a new oven lamp. There were two 110v lamps wired in series, can't remember the base, and yes I tried US suppliers.
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Old 4th May 2018, 9:07 pm   #25
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Default Re: 1980s Pansonic microwave - repairable?

Its a high voltage diode, your meter has not enough volts to test it.
Try a 12v battery and a small bulb if you have one. Or put it in series with a 25w light bulb ( the one in the microwave ) across the mains, you should see it's not as bright as when just on the mains without the diode.

There is a microwave spares company on the Isle of Wight for any spares.

Last edited by Boater Sam; 4th May 2018 at 9:09 pm. Reason: added
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Old 4th May 2018, 9:49 pm   #26
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Default Re: 1980s Pansonic microwave - repairable?

When my HV Diode failed I found a replacement cheaply on Ebay plus the correct fuse.
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Old 5th May 2018, 1:42 am   #27
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Default Re: 1980's Pansonic microwave - repairable?

It would probably be smart to replace the HV cap while you've got it apart, saves doing the job twice (while not overly common for them to fail completely they do lose capacity).

We would replace everything in the HV circuit (except Magnetron unless faulty) as a matter of course if we had a microwave with a HV fault.

Re Australian spares company - Statewide Appliance Spares or the online one?
I'm pretty sure Statewide will ship overseas, but if you get stuck, pm me.
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Old 5th May 2018, 4:05 am   #28
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Default Re: 1980's Pansonic microwave - repairable?

The company on the Isle of Wight is Magsells Ltd. They have a web site.

I ordered a capacitor for a Panasonic microwave.

I have no connection with them apart from being a satisfied customer.
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Old 5th May 2018, 7:33 am   #29
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Default Re: 1980's Pansonic microwave - repairable?

Another very regular fault with microwave ovens was the 'Lucar' connections to the high current Magnetron heater. I used to replace the connectors to ensure reliability. John.
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Old 5th May 2018, 12:36 pm   #30
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Default Re: 1980's Pansonic microwave - repairable?

Is the 0.5A fuse a fast blow or anti-surge type?

I assume it is 6.3mm x 32mm fuse and connected to the chassis at one end.

I would be very tempted to verify the diode is OK, solder in a new fuse, insulate it well and see what happens.

If it works you can then invest in new parts and do a proper job.
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Old 5th May 2018, 1:18 pm   #31
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Default Re: 1980's Pansonic microwave - repairable?

The original is likely to be a long high voltage fuse but using an ordinary one for a quick test is a good idea, but if it works, use a proper long one.
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Old 5th May 2018, 3:03 pm   #32
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Default Re: 1980's Pansonic microwave - repairable?

I seem to remember a common fault on many Panasonic ovens was the HT fuse blowing due to the capacitor being short circuit, i think the value was something like 0.91 Mfd or similar, a simple repair.
check the capacitor for short circuit after of course shorting it's terminals to discharge it just in case,
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Old 5th May 2018, 6:20 pm   #33
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Default Re: 1980's Pansonic microwave - repairable?

Here is my own experience servicing microwaves, it's actually a copy and paste from a post I made a few years ago, when it was fresher in my mind than it is now:


Usual failure modes need discussing These are in the order of likelihood in my own experience, with the most likely first.
The HT diode goes short or leaky.
The HT capacitor goes short.
The magnetron goes short anode to cathode or overheats and cracks one or both magnets (can be seen with a careful visual inspection).
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Old 5th May 2018, 6:26 pm   #34
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Default Re: 1980's Pansonic microwave - repairable?

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Originally Posted by Terry_VK5TM View Post
Re Australian spares company - Statewide Appliance Spares or the online one?
I'm pretty sure Statewide will ship overseas, but if you get stuck, pm me.
Hi Terry,

The company I found is Telespares.com.au of Melbourne. I did a lot of googling and found that they supply the complete diode + fuse assembly for $5 + shipping. According to the website it is already in the mail to me. I think you are right about replacing the cap whilst I am at it. I'm sure I can source one of those more locally.

Thanks everyone else for the very helpful guidance and suggestions. I'm bowled over by the number of responses to this thread. All are read and appreciated!

Steve
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Old 5th May 2018, 7:00 pm   #35
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Default Re: 1980s Pansonic microwave - repairable?

Quote:
Originally Posted by julie_m View Post
If the magnetron has had it, the oven has had it.
Magnetron tubes are generally interchangeable. One type will often fit tens of models from different brands, so all is not lost.
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Old 5th May 2018, 7:05 pm   #36
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Default Re: 1980's Pansonic microwave - repairable?

I think I've just found a homebrew HV probe calibration voltage source
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Old 5th May 2018, 7:30 pm   #37
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Default Re: 1980s Pansonic microwave - repairable?

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Magnetron tubes are generally interchangeable. One type will often fit tens of models from different brands, so all is not lost.
That's very true, and I harvest the major parts from discarded microwaves to keep in stock to repair my own should the need arise.

One thing to watch about "universal" replacement magnetrons, there are at least three mechanically different orientations of connector and heatsink fins, relative to the mounting plate.

Also, if you are tempted to harvest the ring magnets off a dead magnetron, do not crack or crush the ceramic insulator at the business end, as it contains toxic beryllium oxide.
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Last edited by Graham G3ZVT; 5th May 2018 at 7:36 pm.
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Old 5th May 2018, 8:53 pm   #38
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Default Re: 1980's Pansonic microwave - repairable?

That's true. When our Magnetron failed I harvested five or six from scrap ovens, and none of them would fit! I have repaired a couple of others with blown fuses, and just replacing it cured the fault.
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Old 5th May 2018, 10:55 pm   #39
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Default Re: 1980's Pansonic microwave - repairable?

I have seen a few microwaves beside mine now where the EHT fuse has blown.

They all seem to use a 6.3*40 mm. fuse in a fat plastic holder nowadays; parts shops will sell you the complete assembly (and sometimes need the 6.3 crimp connector changing for a 4.8 one) for about a tenner (the guy who sold me mine even crimped the right one on for me, for nothing) but if you can wait for the Slow Boat from China, you can pick up five of just the glass fuse inside for a couple of quid. It's probably worth cleaning the glass after you've handled it, as with halogen lamps, lest you leave any conductive deposit which could arc across if the fuse "succeeds" (it can hardly be called a failure, if everything but the fuse survives intact as intended).
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Old 6th May 2018, 9:06 am   #40
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Default Re: 1980s Pansonic microwave - repairable?

Quote:
Originally Posted by rambo1152 View Post
The oddest one was the Breville I had to write off because I couldn't source a new oven lamp. There were two 110v lamps wired in series, can't remember the base, and yes I tried US suppliers.
our old sharp was the same, used a slightly smaller than SES base, in ~2005 managed to get a replacement bulb ordered from our local repair shop (Cockings in Weymouth ) and after me describing the bulb knew exactly what it was. Even ended up with a genuine sharp replacement!
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