Defeating Tricky Microwave Anti-Repair Techniques

Eric

This upper-end Panasonic microwave oven stops working after only one and a half years. Panasonic only offers a one-year warranty. The point of sale merchant is unhelpful too. A repair technician is bound to cost a lot, but hey, maybe I can get it working. Let’s open it up and look for clues.

Anti-Tamper Screws

Thank you Panasonic for introducing me to security or anti-tamper screws that prevent ordinary tools from opening the microwave. You can find these screws in public places like display kiosks and auto-flush toilets. After a lot of Googling, I found out there are many propriety anti-tamper screws. Mine are called Security Torx screws, and even it has many variants.

Torx security screws on the microwave
Torx security screws on the microwave

I have no idea what my variant is, so I’ve set mind to finding a screwdriver set. Amazon is reasonable, and so is AliExpress. Home Depot is unreasonably expensive. Canadian Tire, on the hand hand, carries a beautiful 47-piece ratchet set.

Ratchet screwdriver set with Torx bits
Ratchet screwdriver set with Torx bits

Let’s unplug and open the microwave up.

Microwave cover removed
Microwave cover removed

Hard to Find Special Fuse

The first investigative step was also the last step – the multimeter showed that the fuse had blown. It’s hard to get to, so I removed some grounding wires, took out the power board (after enough time had elapsed for the capacitors to safely drain), and removed the fuse.

Microwave power board removed
Microwave power board removed

Here is a close up picture of the blown fuse. It’s pretty. A lot of current must have blown this fuse, or a long microwaving session could have heated this “special fuse”.

Blown 250V 15A ceramic fuse
Blown 250V 15A ceramic fuse

But wait, let’s look at the power board again.

Special fuse required
Special fuse required

What is special about this fuse? From the markings on the fuse it is a 250V 15A ceramic fuse. Back to Canadian Tire, here are the only 250V 15A fuses – reassuringly called “microwave fuses” – that they carry.

Replacement 250V 15A ceramic microwave fuses
Replacement 250V 15A ceramic microwave fuses

Do they fit? Well…

Fuse overhang from the special fuse holder
Fuse overhang from the special fuse holder

Sadly, they do not fit. The only replacement fuses available do not fit – they are too long. It turns out the readily-available microwave fuses are 30mm long, but the fuse I need is inconveniently 20mm long. Perhaps I’m just unlucky and Canadian Tire doesn’t carry them. Instead of taking a third trip there, I searched online on Amazon.ca for shorter replacement fuses. Here is what I found.

Microwave fuses found on Amazon
Microwave fuses found on Amazon

There are none of these 20mm fuses available on Amazon either. That’s pretty tricky. In my case, I unsoldered the OEM fuse holder and extended it with a little metal working (not pictured). Good as new.

Update: Jan 20, 2019 – One month and US$2 later a package of ten 20mm 15A fuses arrived from AliExpress. I’ll hang on to these for friends.

Proper 20mm fuses arrived from AliExpress
Proper 20mm fuses arrived from AliExpress
To recap, the special fuse used in the upper-end, newer-model Panasonic microwave is protected by anti-tamper screws, and is shorter than the readily-available longer fuses. Why is Panasonic using “special” fuses? Do they have a surplus? My suspicion is that, coupled with a short warranty and the anti-tamper screws, Panasonic has their own shorter fuses and is profiting on carry-in repairs or buying new microwaves. They can be repaired at home. Extend the life of your microwave.