Possibility #1:

You're conflating scenes from two different movies: The original, in which the special effects now seem outdated and unconvincing, and the sequel, in which the special effects still hold up pretty well today.

Possibility #2:

The scene doesn't exist as you remember it, and never did. You have essentially created what is known as a "headcanon". It happens all the time. For example:

• There are tens of thousands of people, if not more, who insist that they saw a version of Star Wars: Episode IV - A New Hope that was actually never even filmed: these people claim that, in the scene where Luke and Leia use a grappling hook and rope to swing across a chasm inside the Death Star, Luke throws the hook, misses, retracts the rope, throws it again, and only then does it catch. In reality, every version of the movie ever released has Luke succeeding on his first try.

• Tons of comic book fans swear there is an issue in which a paramedic lifts Mjolnir. Again, never happened.

The same rule probably applies to individual and iconic lines that people "quote" from famous movies and books, which were never actually said. Such lines are known as "Beam me up, Scotties". Some examples:

• "Play it again, Sam": I've never seen Casablanca, but I have associated this line with the movie for as long as I can remember, as have tons of people who have seen the movie and loved it. But no one ever says this in the movie. The actual line is "Play it once, Sam, for old time's sake."

• "Luke, I am your father": Vader actually says "No, I am your father".

• "Beam me up Scotty": Since the 70's or earlier, people have considered this the most recognizable Star Trek dialogue ever spoken. Unfortunately, it never was spoken in Star Trek media until the last few years. Before then, the closest variants used onscreen were "Scotty, beam me up", "Beam me up", and "Beam us up, Scotty".

• "Just the facts, ma'am.": The only thing most people know about Dragnet is this line, which was never uttered on the show.

Possibility #3:

Totally different movie. Not much we can do about that.

Memories get altered with age. You might just thought it was cooler before. Just a thought. But watching the video, they vary between beams and blasts. The rapid fire of the tanks also make multiple blasts blend together into beam shapes. At 57s you see a few blasts (with pew pew pew sounds), and at 58s you see a pair of beams (without pew pew sounds).

As far as I know, there has been no revamped or modifications to that scene. It would not make fiscal sense, especially for early 80s special effects. It's not cheap. And it doesn't fix a continuity or plot issue.

From the IMDb list of Alternative Versions for Terminator the most significant changes on a non-tv airing are:

The new MGM R1 DVD releases has two altered scenes, at the request of Lightstorm Entertainment, supposedly to fix goofs in the original picture: a scene set in the future, when a Terminator enters the rebel compound, has been flipped on its vertical axis; the scene where the Terminator leaves the motel in L.A. has been cropped/reframed so that his feet are no longer visible (this was done to fix a continuity problem: the original scene showed Schwarzenegger wearing shoes instead of boots as previously seen).

The rest of the changes are remastering, minor continuity, and broadcast edits for gore/sex/time.

_{And it's not a Lucas special edition.}

So it's completely possible that A) you have mistaken the scenes for something they were not, or B) you're thinking of another movie.