How to know my balancers are due for replacement?

A home owner from toronto canada says:
My existing tilt windows are using this balancer (S600-26) in terms of measurements. None of my windows stay up when opened so I needed to insert a block under the window to stop it from falling. I tried to re-adjust the existing balancers, none of them has any tensions. I wonder if the new ones has the retractable tension as I do not know how it is supposed to work. I am guessing I need to replace all my balancers but i want to make sure before buying any. Is there a way I can test so that I know my balancers are really due for replacement?
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Donna from SWISCO responded:
If you turn the spiral and it keeps spinning around without gaining tension, you need new balances.
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