Consider the circuit of Figure 4-41. Output Y is supposed to go HIGH for either of the following conditions:

1. A = 1, B = 0 regardless of the level on C

2. A = 0, B = 1, C = 1

You may wish to verify these results for yourself.

When the circuit is tested, the technician observes that output Y goes HIGH whenever A is HIGH or C is HIGH, regardless of the level at B. She takes logic probe measurements for the condition where A = B = 0, C = 1 and comes up with the indications recorded in Figure 4-41.

Examine the recorded levels and list the possible causes for the malfunction. Then develop a step-by-step procedure to determine the exact fault.

Figure 4-41

Transcribed Image Text:

A B 2 +5 V 14 Z1 X 5 13 12 Z2 +5 V 14 Z2 ន 61 10 11 ICs are TTL Z1: 74LS86 Z2: 74LS00 72 ន Pin Z1-1 Z1-2 8 Z1-3 Z2-4 Z2-5 Z2-6,10 Z2-13 Z2-12 Z2-9,11 Z2-8 Condition LOW LOW HIGH LOW HIGH HIGH HIGH HIGH LOW HIGH