Troubleshooting Dynamic Digital Circuits - Wavetek 75 Instruction Manual

6.2.2 Troubleshooting Dynamic Digital Circuits
Most of thedigital circuits in this instrument aredynamic.
Even with no changes made to the instrument setup,
LOGIC
1
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internal circuits are running and lines are changing
states. This makes troubleshooting difficult without the
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STATE
use of powerful tools, a logic analyzer for instance.
There is, however, a technique using an oscilloscope
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which will usually help isolate an abnormal signal. The
basis of this technique is looking for stuck bits. A normal
digital signal will switch between a logical "1
"
(a high)
and a logical "0" (a low). A stuck bit may not switch at
all. It may be always high, always low, or always between
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logic levels in an undefined state. A stuck bit may also
switch between high or low levels and the undefined
state. Figure 6-2 shows examples of gooddynamic digital
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signals and figure 6-3 gives examples of stuck bits.
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LOGIC0
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UNDEFINED
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STATE
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Figure 6-3. Defective (Stuck Bits) Digital Signals
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6.3 TROllBLESHOOTlNG GI.lIDES
Refer to table 6-1 for circuit guide information.
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6.3.1 Power Supply
To determine a faulty power :upply use table 6-3. To
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troubleshoot a faulty power s ~ p p l y use the procedures
listed in table 6-4. For fuse replacement, refer to
paragraph 2.2.3.
Figure 6-2. Normal Digital Signals If the desired results are obtained in each of the steps
in table 6-4, replace either Q1, Q2, VR1, or VR2 as
appropriate.
Scans by ArtekMedia O 2006