And it looks just as ambitious as 1.0
https://brickset.com/article/92419

That's not very good advertising.

so ominous

so bold

so confusing

so 2000s

1.5 was the one that nixed the power jack, 2.0 revamped the parts pack. For those who don't know the story, the RCX 1.0 had a power jack built in so you didn't need to feed it batteries. Problem is, the adapter sold by TLG was expensive, and people who wanted to barebones it frequently hit places like Radio Shack to pick up a universal power adapter. And they didn't realize that the RCX had a 9v _AC_ jack, not a 9v _DC_ jack. AC splits the power load between two power busses, while DC runs the entire load in on one. If you ran it with a light load, you could get away with this and not realize you'd made a mistake. If you maxed out the load capacity using a DC adapter, however, you'd blow out that power bus as it was only designed to handle 50% of the load. You could flip the polarity and keep using it, but if you put too much load on it a second time, you'd burn out the other side of the power bus and render the jack completely useless. People of course complained about this, and the solution was to just eliminate the power jack altogether because people can't be trusted to use their toys the right way. When the NXT replaced the RCX, they did restore the power jack, but rather than putting it in the expensive NXT brick, they put it in the Li-Poly battery pack. Since the battery pack plugs into the same battery compartment that you'd use with alkalines, the NXT got the same power regardless of whether it was from regular batteries, the Li-Poly pack, or wall power being fed through the Li-Poly pack. Problem solved. Until they upgraded once again to the EV3 and did away with the rechargeable battery pack.

This set probably affected my life more than any other set, and for that matter, more than any other product. It was my first real introduction to engineering and programming, and the early 2000's Mindstorms ecosystem was fantastic for both education and play!

This picture surely sells itself.

@PurpleDave said:
"AC splits the power load between two power busses, while DC runs the entire load in on one. "

Sort of, but not really.

Lego definitely screwed up badly, since they did use AC input on the RCX 1.0. No competent electrical engineer would have designed it that way, because the actual electronics are all DC, and you'd have to put a AC/DC rectifier in the RCX that's only used when the AC adapter is used. This is wasteful, takes up board space, and creates more points of failure.

What was actually happening isn't what the misinformation you've read on the internet actually says, because there are no two "power busses". What the RCX 1.0 had is a very simple rectifier, basically a pair of diodes wired in parallel, facing in opposite directions, between the power jack and the rest of the on-board power circuit, that converts the AC to DC. The problem with feeding DC into the power jack is you run all power through only one of those diodes, while AC input roughly splits the power between both diodes.

If Lego did something stupid (which we already know they did by choosing AC input), they sized the diodes based on half the total power, and didn't leave enough safety factor to prevent a single diode handling all of the power from burning out.

Most likely what happened is people used low voltage DC power supplies, and ended up running too much current through only one of the two rectifier diodes (current times voltage equals power). The solution, at least before you burn out one of the rectifier diodes, is to just up the voltage. AC voltage is usually specified in voltage RMS, not peak voltage, but the diodes still need to handle the peak voltage. 12V AC RMS is about 17V peak, so we know the power circuit that comes after the rectifier must handle at least that much safely and reliably. If we feed the RCX power jack with 15V DC, we end up with only about 60% of the current as we had with 9V DC, which would be easier on the rectifier diode that is doing something.

If you have burnt out one or both of the rectifier diodes, the solution would be to either bypass them (wire the power jack to the board behind the rectifier) or replace them with plain wires, since you don't need the rectifier functionality if you're feeding DC into the power jack. You DO need to make sure the polarity is right at the jack, since the rectifier also serves to prevent reverse voltage from being fed into the rest of the power circuit.

Ah, I love it when instruction images are used instead of a box image when the instructions were never meant to be the face of the set. But alas, here we can at least see the cool instruction cover.
If you wonder what the set looks like it's this one by the way:
https://u-mercari-images.mercdn.net/photos/m67799023778_6.jpg

I remember it from the catalogs, as I didn't have 1998 or 1999 catalogs so I never exncountered version 1.0. The presentation was something else back then!