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Originally Posted by ostlar
Could a diode or resistor fail while being loaded, but otherwise measure okay unloaded? Or it might be the IC as you say.
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A diode or transistor can fail under load, but test okay. The junctions can degrade and stop working to spec. A resistor is almost impossible to test perfectly and fail under load. There's some really edge cases where the body of the resistor has a small crack that heats up and separates when under load, but it almost always goes complete open, and if it was cracked, it would fall apart in your hands when you took it out of circuit.
One trick to isolating a bad semiconductor is to spray it with cold spray while it's on. Sometimes the quick change in temperature corrects the problem momentarily. Doesn't always work
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The IC costs $10, so it is very tempting to order and replace it.
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There's voltages shown on the schematics for the IC. I think it would be a good idea to check them out, although I'm not 100% sure that they are all good to probe. Sometimes those areas can be tricky, but the service literature usually tells you not to probe them if so. Just in case, I might use a multimeter I didn't care a whole lot about for the first test.
Or hopefully someone else here can chime in and give the go ahead.