On Mon, 8 Jun 2020 00:02:34 +0100, Andrew wrote:
Hi, I have an NN-A554W and the transformer on the inverter board has
blown. Microwave wouldn't start cooking so I ran it for a moment with
the cover off, transformer did a light and smoke display and now it
smells like fireworks.
Impressive. I know how you feel:
http://www.learnbydestroying.com/jeffl/pics/drivel/#burned-yam.jpg
That's what happened when I cooked a yam (potatoe) for 16 minutes
instead of 6 minutes. It was glowing bright red inside just before I
opened the door. The inside of my Panasonic NN-S533WF (Sensor 1300w)
microwave oven changed from white to yam colored. I tried to clean
it, but the yam color is permanently baked into the paint. The S/N
label says made in 2003. I think I received it as a present in 2005,
making it 15 years old. It works as well today as it did in 2005 with
no change in output level. That's one of the benefits of an inverter
oven.
I made sure the magnetron was discharged and between the two connections
I am getting 0 ohms, but I only have a basic multimeter. Between those
and the casing is open.
Try measuring again with a much better ohmmeter or preferably an ESR
meter, which will measure resistances below 1 ohm. The two terminals
on the magottron are the filament wires. Less than 1 ohm is typical
and is easily mistaken for a short circuit.
"Magnetron Test for Opens, shorts or Insufficient Power"
https://www.microwavespecialties.com/pdfs/E10-2010-06%20Mag%20Test%20Bulletin.pdf
The instructions are for a commerical oven, which may have more than
one magnetron inside, but the methods are the same for a home
microwave oven with only one magnetron.
This microwave is at least 10 years old with a lot of use, so how likely
is it that the transformer has just gone by itself vs the magnetron or
the small mains input board dying and taking the transformer with it?
Near zero. I haven't repaired too many microwave ovens and only one
inverter oven. Mostly, what I find are (in order of frequency):
1. Blown high voltage diodes.
2. Blown high voltage capacitor.
3. Blown thermal protection fuse.
4. Filthy and intermittent door interlock switch.
5. Low magentron output or dead magnetron.
I would guess I've fixed about 20 mw ovens and have yet to see a blown
high voltage transformer. If the enamel coating on the torroid are
discoulored from overheating, you might have a problem with the
transformer. If it looks normal, it's something else.
You might want to try searching on YouTube for videos on how to
diagnose and repair microwave ovens. This looks like a good start:
https://www.youtube.com/watch?v=hBJJU4ZRh7U
The other thing is that the part number of the inverter/transformer
board is A6645M304GP, and the magnetron is a 2M236-M42. A lot of other
models seem to use boards that look identical, but not exactly the same
part number. For example I have found a site saying that this magnetron
can be used with an A66454T05AP or F66454T07AP board, which do look the
same as mine, so are they just a different revision or something or are
the differences going to be bigger?
What you're seeing are differences in part number because the
manufacturer sourced their magnetron from multiple (Chinese) sources.
Each source has a different part number, but are functionally and
mechanically identical. The NN-A554W is a 1000 watt oven, so any 1000
watt magnetron that mechanically fits is likely to work.
Even if I need exactly the same board, it looks like I could be chasing
a part that would work in many different models, even different brands,
if only I knew which one to look for (it seems there are no parts for my
model).
No parts? Google is your friend:
https://www.google.com/search?q=NN-A554W+oven+parts
Hmmm... are you in the UK? The Panasonic model number seems to be a
UK only 230VAC oven?
Am worried about replacing it and having the new one get instantly blown
up though.
Well, if you want an exact replacement, it would helpful if you would
supply the full model number. Is it NN-A554WB or NN-A554WF ?
If you have no clue what you're doing, and are lacking in basic test
equipment, I would recommend:
1. Checking the magnetron with an ohms guesser.
2. If ok, replace the Hi-V diodes and Hi-V capacitor.
3. If that doesn't fix it, don't replace the magnetron. Instead by a
replacement inverter board. It's one of these:
https://www.kitchenwareonline.com/panasonic-microwave-oven-hv-inverter-m3ffzz000bp-c2x13938345
https://www.kitchenwareonline.com/panasonic-hv-inverter-for-microwave-ovens-z606yba00gp-c2x15619538
4. If that doesn't fix it, it MIGHT be the magnetron, but I doublt
it. Magnetrons usually fade away slowly, where cooking takes longer
and longer, until it doesn't cook. It does not die suddenly or belch
fire. If you bought a replacement board, you've probably spend more
on the repair than the oven is worth. I suggest you cut your losses
and just buy a new oven.
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558