we used 74LS02p..
im bad in understanding english..
how is it become a poor practice of using pulldown?
I explained it in post #12, but I'll say it again in different terms:
TTL logic low input current, through a resistor to ground, raises the logic zero voltage above ground. In 7400 series TTL, a 1k can raise the logic low voltage by a volt or more. This is above the minimum VOL of 0.8V. I know you are not using 7402s.
In 74LS logic, 1k can raise the input voltage by as much as 0.4V. This is OK, because it is well below the minimum VIL of 0.8V. However, to raise the input to the minimum VIH of 2V, you must supply (2V/1k)=2mA per load. In your circuit, some of your outputs have to drive two 1k loads, with a diode in series, which further reduces the available current. A 74LS gate output, worst case, may not be able to do this, as VOH is 2.7V minimum at 0.4mA load. There is no spec for the available current at Vout=2V.
The bottom line is, TTL inputs require a (relatively) high current for logic low inputs, and outputs are designed to provide that current. Logic high inputs require 20uA max, so the outputs are not designed to provide much sourcing current when high. This makes driving resistive loads to ground more difficult than driving loads to Vcc.
PS I just noticed that your capacitors have no discharge path. You need a resistor to ground from each diode cathode.