Dim LEDs on circuit board

The constant 10-15VAC is a measure of the the received signal in the circuit.

Your line of thought as to the observed unusual perfomance of the circuit are all relevant possibities.

In addition to the suspected grounding issue, i suspect component malfunction (something like leakage)

Check the active components to confirm.

Cheers,

ethobil

Thanks ethobil,

But I'm not sure what the active components would be. There is simply some sort of "gated" signal that accompanies an alarm condition. One to the piezo buzzer and one to the led boards. Obviously, the one to the buzzer is working fine. I would assume, it's the same signal going to the led board. I should note one more thing. I was asked to fine tune someone else's work here, and while checking for power loss (there was -23.7V DC at the last input after daisy chaining through 3 units, a loss of 0.3V) I noticed that polarities were reversed. I traced it all the way back to the first splice after the power supply and corrected it. That's when I noticed the leds not working. In my past experience, when the DC polarity is reversed like that, either the power supply fuse or board fuses blow. Not in this case. The units seemed to work OK. Perhaps whatever component controls the "gated", or "pulsed" signal under alarm condition was damaged. What sort of component would do this though? A Diode?

HI,

I guess that you may be switching the LEDs too quickly... What is the frequency of switching ON or off the LEDs???

Also are you taking care of the driving current requirements... Like how many LEDs are you using in that series arrangement of yours... etc... could you provide more details...

are you using an LED Driver. Are your outputs ports properly biased(pull up, pull down...) or are you using a relay to just turn ON and OFF a series of LEDs

You many need to play around with the resistor values to find a suitable 'brightness' for the LED's. Increasing/decreasing the resistance would affect the illumination.

Give this a try...it should work.

Regards !

1. A block-diagram of your set-up may help to offer some reasonable tip.

2. << Additionally, voltage is sent through a 2 conducter in a metal pipe to another board which contains leds in series. >>

Is this voltage a constant DC & you have connected one of the LEDs a "Flashing LED" in series or

the supply to LEDs-Bd is Pulsed? at what rate /minute ? Mark/space [on-time/off-time] ratio?

3. As suggested by Skeeter << #3 ... I suggest you disconnect the 2 conductor input to the leds and substitute an input voltage that you know to be correct. >>

This is the standard practice of fault-finding "To Isolate" Sections of system & start from the section you notice not working; in your case "LEDs Board".

Thanks all. Excellent advice. Unfortunately, I don't have all the necessary info. not really sure what is driving the leds. I know it's supposed to be 15V and I assume it should be DC, as the feed is 24V DC. I'm thinking now that the flashing is controlled on the return end somehow. If inadvertently grounding the leds caused them to light up, perhaps there's supposed to be a constant supply to them, and some component switches the loop at the ground end, and this component is faulty due to the reversed polarity. The unit is at another location that I am not close to, so it's hard to test everything. The bottom line is that the board can be replaced for about $500, and is probably the smartest thing to do. I just couldn't understand why the leds would work slightly, but not bright enough. I know they are good, as I mentioned the accidental lighting when grounded to the metal pipe.

Sorry i didn't come back ealier than now due to an issue with my Internet connection.

Replacing the board could be an overkill. Following the isolation method suggested previously by Skeeter could get you the desired result.

Meanwhile, looking at a simple RF antenna circuit, the active componet i suggested is a transistor.

cheers,

ethobil

I am wondering if there is anything else wrong with the led board, other than that the leds are dim, or do not function, during an alarm. If the leds' only function are to flash, during an alarm condition, could you not just substitute another led flasher, which would trigger, during an alarm?

I am wondering if the piezo component is the right one for the circuit to begin with. If this is something that was put together by another individual they may have installed a "make do" component before you got the project. One other thing, have you done the old "cold shot" troubleshooting method yet? I know some guys don't like to use that old method, but what the heck...You may have a bad IC run on the board and it may be just tiny enough that your "pipe" enabled a decent ground. Either that the LEDS were undersized to the circuit....Good luck.