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Industrial saw burnt out relay repair

Discussion in 'Troubleshooting and Repair' started by tvrulesme, Jun 28, 2018.

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  1. tvrulesme


    Jun 28, 2018
    I have an industrial saw which has stopped working as a relay burnt out (from damp sawdust by the looks of it). It's an old saw and not worth a lot but worked great before this so reluctant to put it on a skip.

    Looking to cheaply replace the circuit board using this identical spec relay

    Looking at the board I am confused by the two red tracks. They seem to suggest a resistor but there has never been one. Is this required or what are these there for?


    The circuit diagram I am working to is drawn below. Does anyone see any obvious problems before I go ahead and order? Many thanks in advance.
  2. Tha fios agaibh

    Tha fios agaibh

    Aug 11, 2014
    It's an option for suppression of voltage spikes when motor is turned off.
    It is probably not necessary on yours but perhaps something they added for larger motor saw models.
    tvrulesme likes this.
  3. tvrulesme


    Jun 28, 2018
    Thanks so much for the speedy reply. If I were to add one, any idea what resistance would be appropriate?
  4. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    Why do you think there should be a resistor? If there never was one, none is required. Possibly these connections are provided for an optional on/off indicator lamp.

    The pinout in your diagram doesn't seem to match the layout of the PCB. It would help to know which components are on the other side of te PCB. Maybe mark the traces on the PCB by the same colors as in the diagram?

    Your diagram doesn't make a lot of sense to me. For one,traces having the same voltage should have the same color (e.g. red instead of black from L1 to the motor), but that's a minor issue. What's (imho) completely misleading is the on-off push button switch. One cannot see which connections are open or closed in the on state or the off state.

    Anyway: Are you sure the relay is out of order? For starters you could try to repair the broken traces by soldering bits of insulated wire between the solder joints as indicated :
    Make sure the wires do not make contact to one another or other copper traces.

    For reference: the pinout of the relay is here:
  5. Minder


    Apr 24, 2015
    In the past I have used copper braid used for de-soldering purposes to repair current carrying tracks, If this is in damp/sawdust area, it would pay to coat the connections after repair with Shellac or Conformal Coating of some kind.


    May 20, 2017
    Looks as though the board is already shellaquared with those burnt tracks. I'd follow the "Minders" advice for repairs.
    What caused the burn out in the first place?
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