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SN74LS47: Not working the same as old ones

Part Number: SN74LS47

I ordered 10 new SN74LS47 to finish a clock. I have a working 60 second count up but when I replace an old SN74LS47 with one of the new 10 that I bought the seven segment counter stops working. I can see that the input to the IC works but there is not output from the SN74LS47. I've tried all ten in the same place as the old ones and none work. I have verified they are in fact all SN74LS47 s. Any ideas?