I've got a dewalt DHS790 compound miter saw. It stopped working this morning.

I've got a dewalt DHS790 compound miter saw. It stopped working this morning. Just blinks the LED once and does nothing.
I tested the brushless motor. All three phases are good. Checked continuity on all wires and they look good. Switch is good
It's advertised as a 120v system, but i'm getting 60v at the switch. I'm guessing the controller ramps up the voltage as needed.
The controllers are all potted shitty mess, but I was able to find one component that looks like a fuse. next picture.
zero continuity. Can you tell if this is a fuse (next fuse)?

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  1. 1 month ago
    Anonymous

    fuse in question.
    if it is and it blew, do I have any options short of finding a new board? It's outputs the 3 phase for the motor so i'm assuming it's the BLDC controller. visibile components look okay I guess.

    What do you think my options are? 700 dollar fricking saw

    • 1 month ago
      Anonymous

      wait, i'm sorry. the board the fuse is on takes the DC voltage from the batteries. and sends it to the board with the FET(?, has a heatsink on it and the 3 red caps?). That board outputs the 3 phase DC to the motor.

    • 1 month ago
      Anonymous

      Sure looks like a fuse. Continuity tester should indicate a short. It looks like it's potted in conformance epoxy, so you could just solder a new one on top. Touch up the old fuse with flux to improve solder flow.

      • 1 month ago
        Anonymous

        I actually just tested it. It has continuity on one side to 1 of the positive battery terminals, but not on the other side. So I think that confirms it's a fuse. I'll try to find another for the other battery. Maybe that's why it's only putting 60v at the trigger? good idea with solding another one on, if i find the other I'll try to get the value

        There’s a short between the saw handle and the ground

        i'll check. It's hard to tell where the ground is going with all the potting. hopefully not through a transistor

        • 1 month ago
          Anonymous

          couldn't find another one. it must be potted in there. but it is sending voltage through the circuit
          the saw is rated for 120v AC at 15 amps, and 2x60v DC(no amperage rating).
          Would a 7.5amp fuse be appropriate given this is isolated to 1 battery or is it different because of it being DC?

          • 1 month ago
            Anonymous

            I don't have hands-on experience with this design – used one but never took it apart – but I would not be surprised if it's two 60V packs in parallel. 120V DC sounds downright scary for a power tool that could get abused. The 120VAC is probably stepped down through a SMPS to provide 60V DC.

        • 1 month ago
          Anonymous

          You need only to probe the two sides with the meter. If you get 0 ohm it's good to go. In situ probing often won't work without isolating the part from the circuit but measuring 0 ohms is one of the few operations that can be done without isolating the components.

    • 1 month ago
      Anonymous

      >The controllers are all potted shitty mess,

      https://i.imgur.com/w3PEoU6.jpg

      I've got a dewalt DHS790 compound miter saw. It stopped working this morning. Just blinks the LED once and does nothing.
      I tested the brushless motor. All three phases are good. Checked continuity on all wires and they look good. Switch is good
      It's advertised as a 120v system, but i'm getting 60v at the switch. I'm guessing the controller ramps up the voltage as needed.
      The controllers are all potted shitty mess, but I was able to find one component that looks like a fuse. next picture.
      zero continuity. Can you tell if this is a fuse (next fuse)?

      Throw them away and make your own

      Jesus fricking Christ there's nothing worth buying

      • 1 month ago
        Anonymous

        It’s potted so you can’t see the microprocessor where they implement the planned obsolescence timer and DRM checking so you can’t use serialized parts from anywhere but an authorized dewalt service depot, or even swap parts from another saw. It’s like the Apple of power tools.

        My radial arm saw goes from the wall, through a mechanical switch to the motor and that’s it.

        • 1 month ago
          Anonymous

          Yea, that's sorta why I said throw that shit out and roll your own driver board.

      • 1 month ago
        Anonymous

        a bit beyond me but i never looked into it.
        can you help me with a 120v setup for this motor?
        obv need the motor controller with i/o(just on or off but ramps power based on load), i don't need the DC batteries so just need lines input to rectification and buck converting.
        interesting project

        • 1 month ago
          Anonymous

          > don't need the DC batteries
          Say what? This stationary saw is battery powered? Lol..Omfg… now I’ve seen everything. Do you clip it on to your toolbelt and take it up into the attic just in case you need to make some cuts? I’d clip mine on in the morning, just in case… I hardly notice it’s there.

          The only possible way I can see getting this turd into someones’ possession is if their wife or gf bought it for them not knowing that nobody needs or wants a battery operated, non-portable, stationary, compound, sliding mitre saw. Kudos to the home depot salesman, he could sell an hour with his dick to a prostitute.

          • 1 month ago
            Anonymous

            No, you bring a small battery pack instead of 1000' of extension cord or a generator to a job site.

            • 4 weeks ago
              Anonymous

              Ahh, that makes sense.
              Only building off-the-grid log cabins in the forest without a pickup truck (smart car?) that can’t carry both that massive saw and a generator is pretty rare though. In fact, it never happened. Every job site I’ve worked at in the last 30 years had power. Even this recent one, basically in the forest.

              • 4 weeks ago
                Anonymous

                I'm with you, it's a niche convenience.
                My reciprocating saw is wall powered, and I intentionally put off work all season because I don't feel like fricking with 50' of extension cord. If it was battery powered I'd by maintaining this place daily

        • 1 month ago
          Anonymous

          Look into ope source brushless motor controllers and steak one if their designs.
          You could probably just buy one for cheap like for an engine or something.

    • 1 month ago
      Anonymous

      >Potted fuse

  2. 1 month ago
    Anonymous

    There’s a short between the saw handle and the ground

  3. 1 month ago
    Anonymous

    Did you check inside the shrink tubing on the battery leads? It looks like those could be inline fuse holders. Probe both ends of both wires first to ensure there is a short. If you have infinite resistance then, cut the shrink tubing.

    • 1 month ago
      Bepis

      This too? Could always jump the fuse with some wire to confirm, but that’s a lot of current.

      https://www.ereplacementparts.com/dewalt-dhs790ab-type-120v-cordcrdlss-mit-parts-c-1009_1163_571008.html

      This website is great for parts, not sure how deep it gets into single electrical components.

      • 1 month ago
        Bepis

        Oooh this is gay. Although sometimes when the OEM parts are overpriced, you can get the correct part # off ereplacementparts and go digging deeper on ebay for aftermarket replacements or better diagrams

      • 1 month ago
        Anonymous

        https://i.imgur.com/I1Bd7Fc.jpg

        Oooh this is gay. Although sometimes when the OEM parts are overpriced, you can get the correct part # off ereplacementparts and go digging deeper on ebay for aftermarket replacements or better diagrams

        It does not look like they view the assembly as serviceable, thus no parts available. A lot of manufacturers do that not as a frick you but because they will not commit to a design. They might change halfway during production without bumping up the model number. Thanks for the reference. Do note that "online list price" can often be as high as twice what a "service partner" pays for. Check on eBay, Amazon and AliExpress for sellers looking to undercut big suppliers.

        • 1 month ago
          Bepis

          Speaking of… there’s a couple different types so here

          https://www.ereplacementparts.com/search_result.php?q=Dhs790

  4. 1 month ago
    Anonymous

    The short is between the handle and ground…meaning you hahahahaha
    Old mechanic joke
    Problem with your car is a short between the seat and the steering wheel…bada tiss

  5. 1 month ago
    Anonymous

    Alright so went to buy a new fuse to solder on and had a consideration.
    If one of the DC batteries were open at one of the fuses, the AC adapter should still work since it looks like it bypasses the DC supply and is rectified and bucked on the AC/BLDC board.
    I checked the power supply thinking it may provide DC, but no it's a big box filled with nothing that supplies 120vAC to the AC/BLDC board.

    So i'm guessing the problem is with this board...

    • 1 month ago
      Anonymous

      Have you checked the parts inside the shrink tubing?

      • 1 month ago
        Anonymous

        yeah they're fine. both are conducting. it doesn't matter though because the AC side

        https://i.imgur.com/UDLeraN.jpg

        Alright so went to buy a new fuse to solder on and had a consideration.
        If one of the DC batteries were open at one of the fuses, the AC adapter should still work since it looks like it bypasses the DC supply and is rectified and bucked on the AC/BLDC board.
        I checked the power supply thinking it may provide DC, but no it's a big box filled with nothing that supplies 120vAC to the AC/BLDC board.

        So i'm guessing the problem is with this board...

        here doesn't work with the AC adapter, which has nothing to do with the DC battery connections. Unless they're rectified on the control board, sent over the the DC side to do ??? and then sent back to the control board.

        I also don't think

        https://i.imgur.com/6nWVVfG.jpg

        fuse in question.
        if it is and it blew, do I have any options short of finding a new board? It's outputs the 3 phase for the motor so i'm assuming it's the BLDC controller. visibile components look okay I guess.

        What do you think my options are? 700 dollar fricking saw

        this is a fuse anymore becuase the resistance is in the megaohms but there is a small .4v drop across it when i hooked the batteries up, which are now powering the system at 20v instead of 60v as before.
        i can usually fix things but this kick my ass today. going to order both boards and hope that fixes it. i really like the saw.

        • 1 month ago
          Anonymous

          You probably have to plug it back into the ethernet to re-register it. Dewalt moved to a service model, and you need to pay $9.99/month for ten 90 degree cuts, or the deluxe package, 100 cuts using compound angles for $29.99. There is a ‘pro’ package but it says ‘call for pricing’
          So whatever you want to do there…

          • 1 month ago
            Anonymous

            Go back to YouTube, Louis.

    • 4 weeks ago
      Anonymous

      >If one of the DC batteries were open at one of the fuses, the AC adapter should still work since it looks like it bypasses the DC supply and is rectified and bucked on the AC/BLDC board.
      Your buck broke. Google it for more info.

      • 4 weeks ago
        Anonymous

        i just bought a new one. a corded only one without all the circuitry. apparently the battery ones have issues with running off 120v AC.
        kept a bunch of parts off the old one and the motor which i'll find something fun to do with.

        potted to hell. i tried heating the potting, soaking it in acetone and just bashing it with a hammer. not much was making the shit come off cleanly and gave up.

        • 4 weeks ago
          Anonymous

          Are you op?
          Get it out of the trash and buy a chink shit bldc controller or give it to me

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