Using this method to find the 4x slot and also maximize winning on the first round.
Insert a number of chips into each slot: 23, 24, 25, 26 and save one.
According to how much we have after one pull, identify the 4x slot.
Then we are guaranteed to have 116 + 1 chips at least, so $117 \times 4 = 468$ for the second pull.