Kokusai Filter Repair

Kokusai MF-455-10AZ Mechanical filters, and others of the MF-455 family, have a habit of failing because the foam which supports the filter after an extended time, decomposes into a sticky, gooey mess, which dampens the vibrations of the resonating disks. These were used in frDX400, flDX400, KW1000, and HA-350 sets, among others. With care, they can be successfully repaired.

Open the filter by bending the four tabs straight up.

Gently pull the filter out of the case by pulling first on one set of legs and then the other in a rocking style. You can see the decomposing foam in this picture

The metal case contains a fiberboard insulator which can also be removed for cleaning. Q-Tips and alcohol work well for cleaning, along with careful scraping with a toothpick or hobby knife. Do not scrape off any metal from the resonating disks. Takahiro Kato reports that nail polish remover works well and others have reported soaking in amonia.

After cleaning, the filter will look like this.

The filter will be supported in the case by cotton pads placed around the filter end disks. Do not pack tightly around the ceramic transducers.

Place the fiberboard insulator back into the metal case and place cotton in each end. Push case back onto base and bend tabs back down to hold filter assembly together.

There used to be a great page on Kokusai filter repair at by Takahiro Kato a Japanese language web site. If anyone ever encounters it again, let me know and I'll put the proper link here.

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