To make a 101R resistor or because it's easier to dissipate the power in two smaller resistors, rather than a larger one.
What's the physical size of the resistors? Are they surface mount? I wonder if transmission lines are a factor.
Surface mount right next to one another, the 68 Ohm are sized at 1206 and the 33 Ohm at 0805 5% tolerance. 68 Ohm is 0.25W and 33 Ohm 0.125W
Thanks Hero999 and eb4fbz!
If they're 5% tolerance, then there would be no sense in having 101R, rather than 100R, so sharing the power dissipation and eb4fbz's comment about minimising the number of different value resistors on the BoM make more sense.
OK, thanks for that, but can you suggest why, having measured them all with Kelvin clips on an in spec Philips / Fluke LCR meter, the 68 Ohm ones are the ones in the 3 inoperative bands, that have gone high resistance, and not the lesser resistance, lesser Wattage 33 Ohm ones please? I would have thought the lesser Wattage lower resistance value ones (and physically smaller) ones would be the ones taking the strain of any glitches? Thanks again, just trying to learn form this as I fumble along
I'm not sure if I fully understand the question.
What do you mean by 3 inoperative bands?
I thought they were both the same power rating, since they're both the same package size, unless one is made from a material, with a higher temperature rating, but that's not easy to tell, just by looking at the PCB.
Of course, for two resistors connected in series, the one with the higher resistance, 68R in this case, will dissipate more than the lower resistance: 33R, so if the 68R has failed, than that would be why. Resistors generally also fail higher resistance, than lower resistance, as some of the element burns away. The only exception is high value, say above 1M, resistors which may arc over, causing some charring, which would reduce the resistance.