While Fools should generally take the opinion of Wall Street with a grain of salt, it's not a bad idea to take a closer look at particularly stock-shaking upgrades and downgrades -- just in case their reasoning behind the call makes sense.

What: Shares of Altera Corporation (NASDAQ: ALTR) slipped about 1% this morning after Goldman Sachs downgraded the semiconductor company from "conviction buy" to "buy."

So what: Along with the downgrade, analyst James Schneider, Ph.D., reiterated his price target of $39, representing about 20% worth of upside to yesterday's close. While value investors might be attracted to Altera's recent plunge -- triggered by a disappointing Q3 -- Goldman believes that a turnaround will likely now take longer than it had expected.

Now what: Goldman sees some near-term headwinds facing Altera. "Although we remain constructive on the medium-term trends for Altera's business (with China Mobile's TD-LTE launch and increased investment in Europe at Vodafone in 2014), we think these catalysts may be further out in time than we had anticipated," noted Goldman. "In addition, we think Altera failed to articulate a clear path to delivering on its operating margin targets in the short term given a lack of revenue visibility." With the stock flirting with its 52-week lows and currently boasting a near-2% dividend yield, however, those short-term concerns might be providing patient Fools with a solid long-term opportunity.