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Two identical circuit boards, one working one not

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wars0696

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I have two identical circuit boards using IC MM74HC123 one manufactured by Fairchild Semiconductor the other by Philips. The Fairchild chip when used in the circuit will announce any length of message the Philip circuit won't announce the longer messages. I don't have a circuit diagram for the board. I only difference on the datasheet is differences in the propagation delay, output transition time and power dissipation capacitance. Could anyone please tell me which of these would course the problem and why?
 

Are you absolutely sure that all of the resistors and capacitors on these two boards are identical? Is your circuit operating at a high clock rate?

The 74HC123 is a dual monostable multivibrator (single shot mv). Unless the discrete components are different/defective on one board, the two boards should work the same if they are really the same. One 74HC123 is pretty much the same as another in low to moderate data rates.
 

Hi!
check the defects in other componets (resistirs and capacitors), i do faced the same problem, then found the resistor has different value as mentioned in color code. to find it took hell lot time

_sree
 

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