I have a panel of LEDs. They are arranged in sets of three. Some have burned out, and I can easily find the offending LED with a voltmeter. But some of them are only on the verge of failing - when the intensity is lower, they work fine. Only when the intensity is turned up do they misbehave, and they don't just go out, they blink, several times per second. My (digital) voltmeter is not capable of capturing that. Is there some simple way of identifying the bad LED in such a set? I would rather not do a trial-and-error desoldering of all three.