The historic studies and many examples we have seen suggested that investors have much better odds when buying stocks on the rise right as they are breaking out of sound bases, not buying stocks when they are pulling back on heavy volume. That is because when they break out they tend to continue higher, and when they pull back they tend to keep on pulling back.  They also teach in the Masters Class that when a stock has its largest loss on the highest volume anywhere on the graph, that action is considered a technical sell signal.  That said, I am looking at ILMN with respect to your question about buying and  inclined to say, "No".

However, there is something to be said if you have a large profit cushion on a stock to where you can choose to ride out a deep consolidation. If that is the case, some investors might hold on unless they start to see multiple technical sell signals occurring.

Now lets add more complexity to the answer by discussing what are considered valid "Secondary Buy Points". Under the fact-based investment system, if an earlier technical breakout from a valid base was missed, they teach in the Masters Class that a stock may be bought following its first successful pullback and test of the 10-week moving average (WMA) - which is similar to the 50-day average, but computed weekly the actual "average" is a slightly different number. It may be bought from that point up to +5% above the latest highs. Always follow the loss limiting sell rules if any position falls more than -7% from your purchase price.

You cannot even consider a test of the 10 WMA line "successful" without seeing at least one good up day, preferably a solid gain with higher and above average volume. A little more damage in ILMN may mean the pullback would not be considered a successful test of the 10 WMA line, it may become a more worrisome violation. By comparison, AMBA bounced back with heavy volume immediately following an abrupt pullback 6/22/15, and it took weeks get any traction after that. The ILMN action may speak more clearly to us in the days ahead. Meanwhile, I'd keep an eye out for fresh breakouts if any new ones show up.