EEVblog #682 – Ness D16X Alarm Panel Repair


Part teardown, part repair, Dave looks at an Australian designed and manufactured Ness D16X alarm panel that has failed.
What’s that smell?
Can it be fixed?
How do you repair solder mask on a PCB?, or add solder mask to your own home etched PCB’s?
And another look at PCB spark gaps.
Previous PCB Spark gap video

Datasheets:
Fairchild F8
Holtek DTMF Receiver
Maxcap Capacitors
Epcos MOVs

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    • tlhIngan

      The other reason for the resistor termination is to handle NO and NC sensors in the same zone. You wire NO sensors in parallel across the input and common lines, while you wire NC sensors in series. The last device gets the resistor.

      Active sensors generally have outputs for either configuration, while passive sensors typically are one or the other (e.g., door contacts);

    • Alan

      The two 35V movs would break down at 70V not 1000V. They would be in series with the center point at ground.

      • Kirill

        70V is the maximum value. MOVs are not precise devices so they would not share current evenly so they are pretty likely to clamp at 60V or even less.

    • Bob

      Hi Dave,
      Do you think that they may have hooked up mains potential to the input and left off the ground? That would explain the 2 MOV’s going between main and ground untouched and the MOV between the main potential lines blown up. It looks like a lot of arcing and damage for a small wall-wart power supply

    • mrkva

      I wanted to ask about the caps – what about smd electrolytics, which go through the oven in the assembly process? They should be able to handle higher heats without drying, no?

    • Artic

      I’m wondering how it’s possible to get a reading in the order of mega ohms when measuring the impedance between the positive and negative terminal of the bridge rectifier (23:20 in the video). Shouldn’t this impedance be extremely low as long as the 2200µF cap is empty?

    • Don Hills

      Looking at the input spark gaps: there’s likely another reason for the serpentine track: impulses such as lightning have HF components. These don’t like bends, which act as inductors. They encourage the pulse to leap the gap at the corners.

    • Rainer

      This rather looks like a slower death, considering the depth of heat impact in the board. Maybe the MOV died slowly, lowering its resistance by time, thus getting hotter and hotter. All of that happened below the current limits of the power transformer’s fuse. So: Long time, raising heat, stinky-poo, but no flash or bang. My 2 cents.

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