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Help with DSC alarm pc2500 smoke detector circuit error

Discussion in 'Sensors and Actuators' started by shawninvan, Sep 15, 2020.

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  1. shawninvan


    Sep 15, 2020
    It now beeps every 10 seconds... when i check the trouble code it comes up as code 7 which is .. Smoke Detector Circuit Trouble ,.,, i did not even know it was connected to any smoke detectors... i tried unplugging the wires that said "fire" on the main board.... no luck... keeps beeping... the manual says when the smoke detector goes off to hit *4 which i did... still no luck.... just keeps beeping.. any ideas would help.. here is a photo of the board..
    when i disconnect the ac power and run off the battery the problem goes away.. weird... help me!


    Moderatores note : removed the huge white space from the picture
    Last edited by a moderator: Sep 15, 2020
  2. shawninvan


    Sep 15, 2020
    the green yellow wire and resistor is the alarm wires on main baord
  3. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    This sounds as if the problem is with the mains (AC) power supply. Have a look a the electrolytic capacitors in thne power supply. Any ones bulged or leacky? Show us detailed photos og the power supply part.
    It is not uncommon for electrolytic capacitors to need replacement after years in service.
  4. ChosunOne


    Jun 20, 2010
    I apologize for taking so long to respond to this thread. I've been having trouble with my internet connection.

    I want to help you. I really do. But I've run into difficulty. I haven't worked on a PC2500 board in, probably, 15 years or more, and I've had to pull up the Installation Manual to refresh my memory. That's an old panel, probably installed in the early 90s, and you should have an Installation manual on hand if you want to keep it working, even if you aren't going to do any of the actual work yourself. Younger service techs might not have the manual, and I had to go through 4 sites before I could pull up a complete and legible copy (yes, there were PDFs of incomplete manuals); so I recommend downloading and printing yourself a copy to keep in the Control Panel Cabinet.
    It's fairly common practice (sad but true) for service techs who don't understand the older panels, simply to condemn them as "faulty" (which does happen, but not as often as they're condemned), and tell you you have to upgrade your equipment, when there's nothing wrong that can't be fixed.

    All that being said:
    Phrasing it that way makes me think I came in in the middle of the problem description. It beeps every 10 seconds now...? Was it beeping more/less often before? I'm going to assume that you mean that it was working fine, and just recently started beeping every 10 seconds.

    From what you tell me later on, and what I can see of the picture of your Control Panel, chances are that your Panel isn't connected to any smoke detector. The panel has a Fire Circuit and looks for 1000 Ohms (1KOhm) of resistance between the "FIRE" terminal and a Common terminal on the terminal strip along the bottom of your Panel. Even if that circuit isn't connected to any device (which it apparently isn't), it's still the Fire (Smoke Detector) Circuit, and it goes into "Trouble condition" if it sees an open circuit or resistance much higher than 1KOhm.

    As it should. Disconnecting wires from the FIRE and/or COMMON of the fire circuit opens the circuit. Instead of 1KOhm, the Panel sees an open circuit, which is a Trouble Condition. If there were smoke detectors wired on that circuit, an open circuit means the Panel can't see their status.

    The smoke detector "going off" means that it triggers an Alarm, which is a completely different thing than a "Trouble". "*4" is used to reset a smoke detector that has gone into alarm, by momentarily disconnecting power to the detector. Hitting *4 should have no effect on a Trouble Condition.

    That IS weird. When you say the problem goes away, do you mean the 10-second beeping stops? But does the system still work when the beeping is gone? Can you use your User Code to toggle Chime Mode on and off; or to arm and disarm the system? In other words, is pulling the AC power just killing the system? What is displayed on the keypad with the AC disconnected? That in itself should cause a Trouble condition.

    One of the first things I suspect with a system as old as yours, is the battery. It's a 12V SLA battery, probably either a 4 or 7 Ah. If it hasn't been changed in the last 5 years, it should be replaced. It's a very common battery you can find in local battery stores, which I recommend because their turnover tends to be more often than online sources. I mention this because weak batteries can give unpredictable ("weird") symptoms.

    As long as the 1KOhm resistor is securely connected between FIRE and COMMON, as it looks like it is in your picture, then your Panel should not have any Trouble on the Fire Circuit. Be sure there's a solid connection where they're screwed in. Sometimes not enough insulation is stripped from the wire ends and the screw is clamped on insulation instead of bare wire.
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