I have a university project that involves working with surface mount LEDs.
For some reason, some of the rows of LEDs, when lit up, are dimmer than they should be. This problem is only intermittent however, and sometimes when the boards are switched off and then back on, they light up fine. This is the issue I need to resolve.
The circuit is 24V constant voltage, made up of several parallel strings of LEDs. Each LED string has 4 resistors and 2 transistors to control current flow.
The PCB they are mounted on has been scored, so that the circuit can be broken into smaller sections if need be. My first thought was that when the boards are snapped along the score line, the copper tracks are damaged, but the LEDs are only dysfunctional on an intermittent basis.
Sometimes, when the LEDs are dimmed, pressing down on the board causes them to light up properly.
I know its a lot of information but if anyone has any idea as to what the problem is, it would be very much appreciated.
Best Answer
This would seem to indicate that you have intermittent connections in the circuit.
It's certainly possible that tracks may be damaged, but it seems more likely the problem is cracked resistors or stressed solder joints on your components.
Check the soldering quality and you might be able to find broken resistors and component connections with either a cold spray or heat gun.