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How to test/check a off delay timer ?

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When I consider which devices might make it a difficult job, I think of a comparator. Its output is either high impedance, or connected internally to ground.

My first experience with trying to get a comparator to operate was frustrating. I could not tell when it was on or off.

For a while I thought I had broken it and had no idea what I did wrong.

So I tried to think of some non-obvious way to detect whether the output was changing. Finally I connected one lead of my meter to the positive supply, and the other lead to the output. That's when I saw the output changing.

The device worked differently than my normal conception of on/off, or high/low.

If the output goes to high impedance after a delay, then you need to find a way to detect when the output is on, or is sourcing current, or sinking current, or is shorting between two terminals.

If the output is tri-state, then it will take a little more ingenuity.
 

I didn't get what i needed to ? I was just asking about how to test / check / diagnose / troubleshoot whether off delay timer has gone bad or its working absolutely fine ..........
 

Assuming the delay is long enough that we humans can observe it...

Then I would hook up an LED (with safety resistor inline) to the output. Connect the other end to ground. (Or connect it to V+ if that's how the output terminal operates.)

An led is obvious when it is on, and it doesn't need much current.

Or, does the timer operate on mains voltage? Then you might try a low-wattage lamp. An led is easy to barbeque hooked up to mains.

Power up the device. See if the LED turns on/off. Whichever it is supposed to do.

Trigger the delay sequence. Watch to see if the LED changes condition after the proper amount of time.

If it misbehaves then you can try disconnecting any components that might be the cause of the problem. This will isolate the output terminal and you can try it again with the LED alone.

If it still doesn't work then you need to isolate it further from whatever circuitry could be causing the problem. It may even require dismantling the device, to test its components.
 

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