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Thread: Takagai TM-1 blows fuse on circuit board

  1. #1
    DIY Junior Member magconpres's Avatar
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    Default Takagai TM-1 blows fuse on circuit board

    A few times in the last year, I've woken up to no hot water.
    In checking the TM-1, there was no power to the remote/display.

    I discovered that one of the 5A fuses on the circuit board was blown.

    Replacing the fuse makes everything fine for at least a few months (like I said, this has happened 3 times in 12 months).

    On one occasion, we had a power outage, so maybe their was a surge when the power came back on, but usually if the power goes out, the unit stays off even when the pwoer comes back on, so I doubt that is it.

    Has anyone else had this happen? My unit is probalby 4 years old now and I'm sure it is out of warranty (though I plan to check).

    whatever it is doesn't happen all the time as a new fuse works for quite a while.

    thanks,

    mcp.

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    ANy clue on what thing that fuse is designed to protect? If there's a schematic, see what the output feeds, then look there.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    DIY Junior Member magconpres's Avatar
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    No clue. Talked with a Takagi tech today. He told me to look for corrosion, leaks, or shorts. I can rule out shorts as if there was a short, this would be a constant problem.
    For now, I plan to relocate the fuse in a panel mounts holder so I can change it easily and I'll monitor the frequency of the issue. If it increases, I'll contact Takagi again.

    The tech did indicate that the discoloration I see on the circuit borad is normal (one corner looks a bit brown...like it's over heating). He also confirmed that the recirc pump is probalby not the cause. He also didn't think that power surges would cuase this. That makes sense to me since there should be a transformer between the line power and the fuse anyway.

    The fuse blew again today, so it's happened twice in 12 days.
    Prior to that it was about 3 or 4 months. Prior to that probably 6 months. So it seems to be happening more frequently.

  4. #4
    Retired Defense Industry Engineer jadnashua's Avatar
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    There's more to some fuses than just their size and current rating...are you sure you're using the right fuse? Some call for a time-delay fuse, this may or may not. Using the wrong one can lead to nuisance blowing like you're seeing. Double-check the spec to be sure.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  5. #5
    DIY Junior Member magconpres's Avatar
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    Blew again today.
    I don't think it is anything with the fuse as the first replacement lasted 6 months, but I will check with Takagi tomorrow.
    Tech didn't think replacing the board would necessarily fix anything, and the board is about $500.

    Everything inside looks pretty good. There's some dust, but nothing much, and there's no water or signs of corrosion at all.

    Will post what I learn tomorrow.

  6. #6
    Retired Defense Industry Engineer jadnashua's Avatar
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    If appropriate (not all circuits are designed for them), a slow-blow fuse can handle a momentary overload and keep the circuit active without blowing where a 'straight' fuse would just melt (blow). This is similar to the trip curve tailoring of most circuit breakers, except you can't reset most fuses!

    If you use a 'straight' fuse in a circuit that is designed for a slow-blow one, you'll often get sporadic blown fuses.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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