I just ran this puzzle last night.
The players entered a large chamber, on the far side was a door leading to the dead king's crypt and all of his treasure. There were 8 stone statues of giant elven warriors arranged around the chamber.
Inside the chamber were 4 pillars, each pillar of which had a shelf and some ancient elven writing (one of the players had both elven literacy and knowledge history, so he was able to read the scripts.) On 3 of the shelves were 3 orbs each, resting in sockets, all jet black and seemingly identical. The fourth pillar had 2 scales on it. The orb shelves were labelled 'The just orb shall pass; the unjust orbs shall be punished'. And the shelf with the 2 scales were labelled 'The scales of justice'. The door to the king's chamber had a socket for one of the orbs in place of a keyhole or door handle.
When the players approached a statue, its eyes began to glow, brighter as the player got closer. The player quickly backed off.
One of the players intuited that the fact that there were 2 scales was significant; if there were only 1 scale you could assume infinite uses of it, but 2 seemed to indicate a limit of 2. The players intuited that the scales were magical and that they could be used to locate the 'just orb'. They also figured out that 9 total orbs was significant: 1 orb to open the door, the other 8 to activate a corresponding statue--obviously a stone golem guardian.
They decided to weigh 4 orbs--two on each side, chosen at random. This means that there was a 4 in 9 chance that one of the 4 orbs was the 'just orb'. I rolled a d10 (1-4, they had the just orb, 5-9 no orb, 0 reroll). The scale balanced, so the just orb was not there. The scale then became fixed; putting more orbs on it didn't cause it to budge. So they had to use the other scale. They had 5 possible orbs left, so they randomly set one aside and weighed another 2 sets of 2 orbs. After another roll (1 in 5 chance that the scale will balance at this point meaning the just orb is the one set aside, so I rolled another d10: 0-9 indicates the scale balances) I determined that the scale did not balance. The orb of justice must be one of those 4. But was it heavier, or lighter, than the others?
An examination of the wall relief gave a clue: a figure wearing a crown could be seen holding a scale, unbalanced, and beams of light were coming out of the higher tray. So the proper orb would appear to be the lighter orb.
That left them with 2 possible 'just orbs'. They randomly chose one, and put it in the socket. I rolled a 50% chance, and, ta-da, they got lucky. Of course, if they had gotten the wrong orb, I would have randomly determined which golem awakened and came to ruin their day. The golems were balanced to be enough of a threat that the party would probably not be able to take on more than 2 of them.
The ideal solution to the puzzle takes luck completely out of the equation. If they had weighed 6 orbs the first time, 3 orbs to a side, they'd have been able to narrow down the just orb to one of 3 orbs instead of 1 of 4 or 5. Then a second weighing would give the correct orb. But ultimately their solution was good enough that they definitely would have been able to defeat the puzzle. They just risked a fair amount of damage from that first golem.