Honeywell ST9103A1002 integrated oil furnace fan control board shorting out

Discussion in 'HVAC Heating & Cooling' started by iwillattemptanything, Mar 9, 2012.

  1. iwillattemptanything

    iwillattemptanything New Member

    Nov 13, 2009
    Stratford, CT
    I have been in my house for 5 yrs now and have gone through 3 of these boards. They burn out in the same spot each time, I have attached a picture. Any ideas what is causing this short in the the board?
    Honeywell ST9103A1002 integrated oil furnace fan control board.jpg
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    Can't really help much without a circuit diagram. If there's an obvious bad part, you might find you can replace it, maybe with one that has a higher current/voltage rating. Intermittent connections can be hell on control boards, so first thing I'd do is double check all of the connectors. This includes the crimps on all of the pins going into the plugs on the board. Some crimps are designed with teeth and you don't have to strip the insulation, some require the insulation to be stripped before crimping. If you needed to have the insulation stripped first and it wasn't you may get a connection with an ohmmeter, but it may not supply the proper voltage or current in a circuit. This can lead to early failure. then, any screw type terminal board...make sure all of them are nice and tight with no stray strands of wire bridging to an adjacent connection. Some serious QA on the system may be all it takes to keep things going smoothly.

    You could also have power problems - frequent brownouts, high voltage spikes, intermittent power connection (wiring, internal, external, bad CB, bad power panel bus connection). I have an add-on device from IDC wired into my HVAC system. It monitors the incoming line voltage and controls an internal SS relay that only closes when the power has been decent for a user preset time (I've got mine set to I think 5-minutes so it won't restart for at least that time after power application). So, as often occurs when power comes back on after a power outage where it may spike and wander all over the place, this keeps things from operating until it stabilizes. Also, you can set the minimum voltage you want it to work at in case of a prolonged brownout, and set the max.

    I'm a fan of whole-home surge suppression. Think of surges as hitting the junctions in solid state devices like attacking a tree with a hatchet. the first one won't bring it down, but do it enough, and eventually, the tree crashes to the ground. The same thing can happen to electronics...some actually come with surge suppression built-in, and some devices aren't very susceptable to them, but if they are, it's best to minimize or eliminate them.
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