Does anyone have a tester for Cat 5 cable I could use for a few minutes?

I've had great success making Cat5 cables up to about 50' but I've made
several 100-footers now, and they don't work.  I have an Ethernet card
with four lights (100, Act, Link, Col) and when I plug any of these 100'
cables between it and the hub, it just blinks the lights in succession
instead of establishing a link.

I've cut ends and redone both ends of the cable, figuring maybe I made a
bad connection or the cable length was "just wrong" (in terms of
reflectivity etc.) but nothing helps.

So now I'm frustrated and not understanding why I can't get a 100' length
to work, when 3', 7', 20' and 50' all work...

Suggestions?

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