Husqvarna TYH 18542 loose deck belt.
The deck belt looked quite loose (probably an inch and a half deflection in the belt half-way from the motor spindle), and the machine would not cut, with the belt fallen off one or two pulleys. I watched some YouTube videos which led me to the cable adjustment. I pushed the adjuster all the way in but that did not make much difference in belt tension, it seemed. I lowered the deck and noticed that the pulley nearest the left side of the mower has a tab which is connected to the tab on the furthest right pulley. But the belt did not go directly from the far-left pulley to the far-right spindle, as shown in the diagram in the front top of the deck. Instead, the belt went inside the tab on the left pulley over to the right pulley, avoiding the tab on that pulley.
I am not clear on the procedure of installing the belt. The manual says to have the brake engaged, and the accessory lever disengaged, I believe. Following those instructions, the belt is very loose. But putting the belt inside the left pulley would probably tighten the belt a bit, I think. Maybe the previous owner tried that to tighten the belt. And another thing-this is a model that Lowe's sold. Perhaps something went wrong in their assembly of the machine.
Anyway, I tried different settings with the brake and accessory lever, set the cable adjustment all the way in, and raised the deck height by turning the adjustment nut about 3 times. And the mower cut grass fine, loose belt and all! Maybe the belt is "correctly" loose? And by the way, the belt looked fine-no shredding or deep nicks.
Thanks for any feedback!